CHILD Syndrome

Mendelian MONDO:0010621 Pathograph 28 Show in embeddings browser sterol biosynthesis disorder X-linked ichthyosis syndrome

CHILD syndrome (congenital hemidysplasia with ichthyosiform nevus and limb defects) is an X-linked, usually male-lethal disorder caused by pathogenic NSDHL variants that impair post-squalene cholesterol biosynthesis. Heterozygous females have variable cutaneous and skeletal involvement, typically with unilateral ichthyosiform lesions and ipsilateral limb defects; bilateral or mild presentations and rare mosaic males are reported. Intellect is usually normal. NSDHL participates in sterol C4-demethylation, and experimental models distinguish effects of reduced cholesterol availability from effects of accumulated intermediates. Patient skin shows abnormal epidermal lipid secretion. X-inactivation creates mosaic expression, but the mechanism of the characteristic body-half distribution and any contribution of longitudinal clone depletion in human skin remain unresolved. Topical statins, alone or combined with cholesterol, have improved skin lesions in uncontrolled reports; these observations do not prove that cholesterol supplementation is required or that congenital skeletal defects are corrected. Hypomorphic NSDHL variants cause the distinct allelic disorder CK syndrome.

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Classifications

Harrison's Part

ICIMD (Inherited Metabolic Disorders)

ISDS Skeletal Nosology

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Inheritance

X-linked dominant inheritance with male lethality HP:0001423

CHILD syndrome is inherited in an X-linked manner and predominantly affects heterozygous females because hemizygous males with severe loss-of-function variants usually do not survive gestation. Rare surviving males with postzygotic mosaicism have been reported. A heterozygous mother has a 50% chance of transmitting the pathogenic variant in each pregnancy; the expected live-born distribution is altered by male lethality. Molecular recurrence-risk assessment requires a pathogenic or likely pathogenic variant, not a variant of uncertain significance.

X-linked dominant inheritance

Show evidence (4 references)

PMID:10710235 SUPPORT Human Clinical

"We report for the first time that CHILD syndrome (MIM 308050), an X-linked dominant, male-lethal trait characterized by an inflammatory nevus with striking lateralization and strict midline demarcation, as well as ipsilateral hypoplasia of the body is caused by mutations in the gene NSDHL located at Xq28"

The gene-discovery paper states the X-linked dominant, male-lethal mode of inheritance alongside the causal locus.

PMID:21290788 SUPPORT REVIEW SYNTHESIS Other

"CHILD syndrome is usually male lethal during gestation and thus predominantly affects females."

GeneReviews states the male-lethal consequence and the resulting female predominance.

PMID:21290788 SUPPORT REVIEW SYNTHESIS Other

"However, since studies suggest that male conceptuses with an NSDHL pathogenic variant generally abort or resorb spontaneously, the expected live-born distribution is: 33% heterozygous (typically) affected females; 33% unaffected females; and 33% unaffected males."

Supplies the quantitative recurrence-risk figures that this description would otherwise only paraphrase, including the reason the live-born ratios depart from the usual X-linked expectation.

+ 1 more reference

Functional mosaicism from random X inactivation

Heterozygous females are functional mosaics because of X-inactivation; this is distinct from a postzygotic DNA variant. In cultures from one studied patient, both NSDHL alleles were present in genomic DNA from affected and unaffected skin. Affected keratinocytes expressed the mutant allele, whereas unaffected keratinocytes expressed the wild-type allele. Affected fibroblasts retained expression of both alleles. This tissue-specific expression pattern does not establish the developmental origin of the body-half boundary or longitudinal clearance of mutant cells in human skin.

Show evidence (3 references)

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT In Vitro

"However, RT-PCR on cDNA from keratinocytes and fibroblasts isolated from the affected versus clinically unaffected side in Patient #1 demonstrated exclusive expression of the mutant allele by affected cultured keratinocytes, while unaffected keratinocytes solely expressed the wild type allele"

Cultures from one patient showed side-specific NSDHL allele expression; this is not a longitudinal measure of cell clearance.

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Only the normal allele was expressed by unaffected fibroblasts, but fibroblasts from the clinically affected area expressed an approximately even distribution of normal and mutant alleles."

Fibroblast expression in affected skin did not match the exclusively mutant keratinocyte pattern.

PMID:11907515 SUPPORT Human Clinical

"Apparently, the effect of random X-inactivation is responsible for different patterns of cutaneous involvement in female carriers of NSDHL mutations."

Attributes the variable cutaneous distribution, including the exceptional bilateral case, to the X-inactivation pattern rather than to allele identity.

Discussions and Knowledge Gaps

What mechanism converts random X inactivation into a body-half boundary in CHILD syndrome, rather than the finer Blaschko-line mosaicism seen in other X-linked genodermatoses?

KNOWLEDGE GAP OPEN lateralization_mechanism_unknown

Attached to

pathophysiology#X-Inactivation-Dependent NSDHL Expression Mosaicism

Expression differences between cultured keratinocytes from affected and unaffected patient skin are consistent with functional mosaicism but do not explain the geometry of the boundary. Age-dependent selection in mouse liver and brain is a separate observation; human skin clone clearance has not been measured longitudinally. Mouse and canine lesion patterns differ from typical human lateralization. Paired spatial and allele-expression measurements could distinguish developmental lineage allocation from subsequent tissue-specific selection.

Proposed experiments

Lineage and allele-expression mapping across the midline in CHILD skin

lateralization_lineage_mapping

Single-cell or spatial transcriptomic mapping of NSDHL allele expression across the midline boundary in affected individuals, paired with clonal lineage inference, to determine whether the boundary reflects an early embryonic left-right lineage restriction, a later selective clearance front, or an unrecognized signalling boundary.

Show evidence (3 references)

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT In Vitro

Cultures from one patient showed side-specific NSDHL allele expression; this is not a longitudinal measure of cell clearance.

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Only the normal allele was expressed by unaffected fibroblasts, but fibroblasts from the clinically affected area expressed an approximately even distribution of normal and mutant alleles."

Fibroblast expression in affected skin did not match the exclusively mutant keratinocyte pattern.

PMID:19631568 SUPPORT DIRECT PRIMARY RESULT Model Organism

"These data suggest that the higher percentage of WT hepatocytes present in livers from older Bpa1H females is the cumulative result of postnatal differences in either the growth rate or survival of WT vs mutant hepatocytes."

Cross-sectional age groups support selection in mouse liver while leaving differential survival versus proliferation unresolved.

Do the placental abnormalities associated with prenatal death in Nsdhl-mutant mice contribute to human male lethality?

HUMAN MODEL MISMATCH OPEN male_lethality_placental_mechanism_human

Attached to

pathophysiology#Placental Labyrinth Dysmorphogenesis

Nsdhl mouse studies associate placental labyrinth abnormalities with prenatal death, but the timing varies by allele and the findings do not establish a universal human mechanism. Rodent and human placental X-inactivation differ. A report of recurrent male pregnancy losses identified maternal and fetal NSDHL c.790-6C>T, but classified it as a variant of uncertain significance, predicted a splice effect without functional confirmation, and tested only one lost conceptus. That report does not confirm NSDHL-mediated recurrent fetal lethality or the placental mechanism in humans.

Proposed experiments

NSDHL-null human trophoblast organoid vascularization assay

human_nsdhl_trophoblast_model

Generate NSDHL loss-of-function human trophoblast stem cell or placental organoid models and assay Hedgehog pathway activity, trophoblast proliferation, and vascular network formation, to test whether the murine labyrinth phenotype has a human counterpart independent of rodent-specific placental X inactivation.

Show evidence (3 references)

PMID:15639195 SUPPORT Model Organism

"X-inactivation is non-random in females in most lineages of the rodent placenta with preferential inactivation of the paternal X chromosome."

States the rodent-specific placental X-inactivation arrangement that the mouse inference depends on and that does not transfer to humans.

PMID:36504312 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"According to ACMG guidelines, the variant has been classified as a variant of uncertain significance."

The primary report explicitly classifies c.790-6C>T as uncertain; its more assertive abstract does not establish causality.

PMID:36504312 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"However, further work is required to verify the relationship between the c.790-6C>T variant and CHILD syndrome."

The authors acknowledge that the variant-disease relationship requires further verification.

How should the historical EBP-positive case labeled CHILD syndrome be interpreted within the current NSDHL-defined disease boundary?

INTERPRETATION OPEN nsdhl_versus_ebp_nosological_boundary

Attached to

genetic#NSDHL

An early report identified an EBP nonsense variant and a CDPX2 plasma sterol profile in a patient clinically labeled CHILD syndrome. The NSDHL discovery cohort instead found EBP unaffected, and current GeneReviews defines CHILD syndrome through NSDHL while listing EBP-related CDPX2 as a differential diagnosis. The early clinical label alone is insufficient evidence of locus heterogeneity. Reassessment of historical cases may clarify phenotypic overlap, but does not justify recording EBP as causative for NSDHL-related CHILD syndrome.

Proposed experiments

Genotype and sterol reassessment of the assembled CHILD case literature

child_locus_reassessment_cohort

Assemble the published CHILD syndrome cases with molecular data, and where material allows, determine NSDHL versus EBP genotype together with plasma sterol profile and lesion distribution, to establish whether EBP-related cases form a clinically separable subgroup or are distributed through the CHILD phenotype.

Show evidence (1 reference)

PMID:10710233 SUPPORT Human Clinical

"We speculate that at least some cases of CHILD syndrome are allelic with CDPX2 caused by 3beta-hydroxysteroid-delta8,delta7-isomerase deficiency."

The authors' own hedged phrasing is the open question this discussion records.

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Pathophysiology

NSDHL Loss of Function

Mechanism confidence: Established

Pathogenic NSDHL variants impair the sterol dehydrogenase/decarboxylase component of the C4-demethylation complex. An expression study of thirteen disease-associated missense variants and one deletion found reduced protein abundance; temperature or glycerol partially increased abundance for some variants. These assays do not establish that all variants act through the same folding defect or that rescued protein has restored catalytic activity.

NSDHL hgnc:13398

sterol-4-alpha-carboxylate 3-dehydrogenase (NSDHL) activity GO:0000252 ⇓ LOSS OF FUNCTION

Experimental models

Heterologous expression of NSDHL missense mutants CELL LINE Measures variant-associated reductions in NSDHL protein abundance and partial abundance rescue in selected conditions.

Animal models

Bare patches and striated mice (Nsdhl mutant) Mouse recapitulates Independent Bpa and Str alleles are mutations in Nsdhl, and tissue sterol analysis confirms the biosynthetic role.

Downstream

Impaired Sterol C4-Demethylation Loss of the NSDHL enzyme component impairs this biosynthetic step.

Increased Receptor Lysosomal Trafficking Experimental NSDHL depletion alters receptor handling; the molecular intermediates and relevance to human skin remain incompletely defined.

Impaired Anagen Hair Growth Nsdhl-deficient mouse skin shows defective anagen progression, with the intervening signaling sequence unresolved.

Ipsilateral body hypoplasia NSDHL dysfunction causes the developmental syndrome that includes ipsilateral body hypoplasia. The intervening tissue-specific processes are unresolved; this edge does not assign the phenotype to a demonstrated Hedgehog or clone-clearance pathway.

Ipsilateral limb hypoplasia or aplasia NSDHL dysfunction underlies the limb-reduction phenotype through incompletely resolved developmental processes. A specific Hedgehog-mediated route in human limbs is not established by the mouse neural-culture experiments.

Show evidence (2 references)

PMID:40222685 SUPPORT In Vitro

"Here we show that protein expression levels were low for all mutants, but some could be rescued by a lower temperature (30°C vs. 37°C) and/or the chemical chaperone glycerol."

The expression assay reports lower steady-state abundance and partial abundance rescue; enzymatic rescue is not established by this quote.

PMID:10710235 SUPPORT BACKGROUND Other

"(NAD(P)H steroid dehydrogenase-like protein) encoding a 3beta-hydroxysteroid dehydrogenase functioning in the cholesterol biosynthetic pathway"

Identifies the enzymatic function that is lost.

Impaired Sterol C4-Demethylation

Mechanism confidence: Established

Impaired NSDHL activity limits removal of C4 methyl groups from sterol intermediates. Reduced downstream cholesterol supply and upstream precursor accumulation are distinct biochemical consequences.

cholesterol biosynthetic process GO:0006695 ↓ DECREASED

Downstream

Reduced Cholesterol Availability The biosynthetic defect can reduce cholesterol availability within affected cells.

C4-Methylsterol Accumulation Intermediates upstream of the enzymatic block accumulate.

Show evidence (2 references)

PMID:15639195 SUPPORT DIRECT BACKGROUND Other

"NSDHL is a 3beta-hydroxysterol dehydrogenase that is involved in the removal of C-4 methyl groups in one of the later steps of cholesterol biosynthesis."

The primary mouse paper describes the established enzymatic function in its background.

PMID:24060582 SUPPORT DIRECT REVIEW SYNTHESIS Other

"CHILD syndrome results from loss of function mutations in the NSDHL gene, which leads to inhibition of cholesterol synthesis and accumulation of toxic metabolic intermediates in affected tissues."

The review describes reduced synthesis and precursor accumulation; these are separate consequences of the biosynthetic block.

Reduced Cholesterol Availability

Mechanism confidence: Provisional

Cholesterol supply can be insufficient within affected cells despite near-normal circulating sterols. In conditional-null mouse granule-cell cultures, cholesterol or LDL supplementation restored much of the impaired SHH response. This does not imply uniform systemic hypocholesterolemia.

Downstream

Impaired Hedgehog Signal Transduction Cultured granule-cell experiments support impaired reception of SHH when cholesterol is limiting.

Impaired Epidermal Lamellar Body Secretion Reduced availability of a barrier lipid is proposed to contribute to the abnormal secretory apparatus; patient ultrastructure and treatment response do not isolate this contribution from precursor effects.

Show evidence (2 references)

PMID:24060582 SUPPORT DIRECT REVIEW SYNTHESIS Other

"CHILD syndrome results from loss of function mutations in the NSDHL gene, which leads to inhibition of cholesterol synthesis and accumulation of toxic metabolic intermediates in affected tissues."

The review describes reduced synthesis and precursor accumulation; these are separate consequences of the biosynthetic block.

PMID:25652406 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Taken together, these results demonstrate that cholesterol depletion is sufficient to account for virtually all of the reduced response of mutant GCPs to SHH in vitro."

Cholesterol supplementation experiments locate a major SHH-response defect in the recipient granule-cell cultures.

C4-Methylsterol Accumulation

Mechanism confidence: Established

C4-methylsterol intermediates accumulate upstream of the NSDHL block. Mouse granule-cell experiments associate precursor reduction with improved viability, but different sterol species and endpoints need separate interpretation. The same intervention did not restore SHH-induced Gli1 expression.

Experimental models

Conditional-null mouse cerebellar granule-cell precursor cultures PRIMARY CELL CULTURE Upstream inhibition reduces precursor accumulation and improves mutant-cell viability without restoring SHH-induced Gli1 by itself.

Downstream

Impaired Epidermal Lamellar Body Secretion Precursor-associated toxicity is a proposed contributor to the secretory abnormality in patient skin; the specific responsible sterols and intermediate steps remain unresolved.

Show evidence (3 references)

PMID:25652406 SUPPORT DIRECT PRIMARY RESULT In Vitro

"The concentration of methylsterols was significantly higher in NsdhlΔ5/Y GCPs than Nsdhlflx5/Y GCPs (P < 0.002) in all four culture conditions."

Cultured conditional-null mouse granule-cell precursors accumulate methylsterols under the tested conditions.

PMID:25652406 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Ketoconazole treatment did not affect the viability of WT cells, but it significantly increased mutant cell viability (from 65 to 78%; Fig. 7B)."

An upstream synthesis inhibitor improved viability in mutant cultures; this supports a precursor-associated injury component but does not identify every accumulated sterol as toxic.

PMID:25652406 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Although the reduction of methylsterol levels by ketoconazole treatment apparently improved the viability and cell morphology of the mutant GCPs, it had no effect on Gli1 expression"

Cell viability and SHH transcriptional responses were experimentally dissociable; lowering precursors alone did not restore this readout.

X-Inactivation-Dependent NSDHL Expression Mosaicism

Mechanism confidence: Established

X-inactivation creates functional mosaicism in heterozygous females. In one patient, cultured keratinocytes from affected and unaffected skin expressed different NSDHL alleles, while affected fibroblasts retained both. These observations do not explain the precise midline boundary or demonstrate longitudinal cell clearance.

keratinocyte CL:0000312 fibroblast CL:0000057

random inactivation of X chromosome GO:0060816

Experimental models

Paired patient skin keratinocyte and fibroblast cultures PRIMARY CELL CULTURE Patient-derived cultures measure side- and cell-type-specific NSDHL allele expression.

Animal models

Bare patches and striated mice (Nsdhl mutant) Mouse partially recapitulates Heterozygous female mice show patches of NSDHL-positive and NSDHL-negative tissue.

Labrador Retriever NSDHL deletion Dog partially recapitulates An NSDHL deletion in two affected females is associated with Blaschko-linear cutaneous disease, consistent with functional mosaicism.

Downstream

Age-Dependent Depletion of NSDHL-Deficient Cells Age-dependent changes in mutant-cell representation occur in mosaic mouse tissues, with differential proliferation and survival unresolved.

Impaired Epidermal Lamellar Body Secretion The patient expression and biopsy findings associate mutant-expressing epidermis with the secretory lesion; the lineage and selection mechanisms producing the distribution remain unresolved.

Strict midline demarcation of skin lesions Functional mosaicism contributes to the distribution of affected skin. The developmental steps producing a sharp body-midline boundary remain unknown, and bilateral patterns can occur.

Show evidence (2 references)

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT In Vitro

Cultures from one patient showed side-specific NSDHL allele expression; this is not a longitudinal measure of cell clearance.

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Only the normal allele was expressed by unaffected fibroblasts, but fibroblasts from the clinically affected area expressed an approximately even distribution of normal and mutant alleles."

Fibroblast expression in affected skin did not match the exclusively mutant keratinocyte pattern.

Age-Dependent Depletion of NSDHL-Deficient Cells

Mechanism confidence: Provisional

Mouse liver and brain show an age-dependent reduction in the representation of NSDHL-deficient cells. This is tissue-specific: NSDHL-negative skin persisted at eight weeks. The mechanism may involve differential survival or proliferation, and the result has not been measured longitudinally in human CHILD skin.

Animal models

Bare patches and striated mice (Nsdhl mutant) Mouse partially recapitulates Cross-sectional mouse age groups show a higher proportion of NSDHL-positive hepatocytes with age.

Show evidence (2 references)

PMID:19631568 SUPPORT DIRECT PRIMARY RESULT Model Organism

Cross-sectional age groups support selection in mouse liver while leaving differential survival versus proliferation unresolved.

PMID:19631568 SUPPORT DIRECT PRIMARY RESULT Model Organism

"The average percentage of NSDHL positive hepatocytes in livers from six Bpa1H P6 females was 52 (SD: 5). Among six mutant livers at P25, the average percentage of NSDHL positive hepatocytes increased to 62 (SD: 9)."

The comparison concerns different mouse age groups and liver tissue, not serial biopsies of human skin.

Impaired Epidermal Lamellar Body Secretion

Mechanism confidence: Established

Patient biopsies show lamellar bodies with few internal lamellae, premature fusion, and incomplete secretion. The resulting retention of organelle material is a cellular secretory defect distinct from the extracellular lipid architecture it produces.

keratinocyte CL:0000312

Downstream

Disorganized Stratum Corneum Lipid Lamellae Incomplete secretion leaves sparse and disorganized extracellular lamellar material.

Show evidence (2 references)

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Individual organelles displayed few internal lamellae, which often fused prematurely into intracellular, multivesicular bodies that were incompletely secreted"

Pretreatment patient biopsies demonstrate abnormal lamellar-body architecture and incomplete secretion.

PMID:16776722 SUPPORT Human Clinical

"Electron microscopy revealed vesicular structures in the intercellular spaces of the stratum corneum and vacuoles or vesicular structures in upper prickle cell layer. Some of them can be recognized as abnormal lamellar granules. Within the foamy cells in the papillary dermis, large vacuoles were found."

Independent ultrastructural confirmation of the abnormal lamellar granules and of the dermal foam cells this description asserts, from a different patient and laboratory than the treatment study.

Disorganized Stratum Corneum Lipid Lamellae

Mechanism confidence: Established

The stratum corneum extracellular matrix in affected skin contains sparse lamellar material mixed with non-lamellar vesicles, consistent with a defective lipid barrier. Clinically unaffected skin can retain mild ultrastructural abnormalities.

establishment of skin barrier GO:0061436 ↓ DECREASED

Downstream

Ichthyosiform nevus The barrier-lipid abnormality contributes to scaling and inflammation. The relative roles of cholesterol deficiency and individual precursors remain incompletely resolved.

Show evidence (2 references)

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Finally, and as a result of impaired secretion, the stratum corneum extracellular matrix displayed a paucity of secreted lamellar material, interspersed with abundant non-lamellar vesicles"

The patient ultrastructure links impaired secretion to disorganized extracellular lipid lamellae.

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Although no visible ichthyosiform features could be appreciated either clinically or by light microscopy, ultrastructural images displayed mild abnormalities in lamellar body internal contents and lamellar bilayer organization"

Clinically unaffected skin from one patient had subtle structural abnormalities, so visible normality is not proof of a fully normal lipid barrier.

Impaired Hedgehog Signal Transduction

Mechanism confidence: Provisional

Conditional Nsdhl-null mouse granule-cell cultures have an impaired response to SHH that is strongly improved by cholesterol supply. Reduced reporter activity is also observed in mouse cerebellum and placenta. These findings concern signal reception and response; defective ligand processing and the precise mechanisms of human limb defects are not established.

smoothened signaling pathway GO:0007224 ↓ DECREASED

Experimental models

Conditional-null mouse cerebellar granule-cell precursor cultures PRIMARY CELL CULTURE Cholesterol supplementation largely restores the proliferative response to SHH, while LDL restores Gli1 induction under the tested conditions.

Animal models

Conditional Nsdhl ablation in radial glia Mouse partially recapitulates Conditional mutant cerebella show reduced SHH target-gene and Gli1 reporter responses in vivo.

Downstream

Placental Labyrinth Dysmorphogenesis The mouse placental reporter and migration findings implicate Hedgehog signaling in the structural defect, without a definitive rescue establishing the full causal sequence.

Show evidence (4 references)

PMID:25652406 SUPPORT DIRECT PRIMARY RESULT In Vitro

"We replicated the granule cell precursor proliferation defect in vitro and demonstrate that it results from defective signaling by SHH."

The experiment is in cultured mouse granule-cell precursors rather than whole animals or human limb tissue.

PMID:25652406 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Using mice that express lacZ under the control of the Gli1 promoter, we were also able to demonstrate variable, but reduced, induction of this SHH response gene in vivo"

A separate reporter experiment demonstrates reduced SHH response in the conditional mouse CNS.

PMID:17028112 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Further, affected placentas from mutant Nsdhl(Bpa-8H) male embryos demonstrate markedly decreased or no Ptch1-lacZ staining and no migration of Ihh expressing cells into the developing placenta."

Placental reporter and cellular-distribution observations implicate Hedgehog signaling in this mouse allele.

+ 1 more reference

Placental Labyrinth Dysmorphogenesis

Mechanism confidence: Provisional

Several Nsdhl mouse alleles show a thin placental labyrinth with reduced fetal vascularization and trophoblast proliferation. Embryonic death occurs at allele-dependent stages, including earlier death with Bpa1H. Placental abnormalities are associated with lethality in these models; the corresponding human mechanism remains unverified.

trophoblast cell CL:0000351

placenta development GO:0001890 ⚠ ABNORMAL

Animal models

Bare patches and striated mice (Nsdhl mutant) Mouse partially recapitulates Nsdhl mouse alleles exhibit a thin labyrinth, reduced fetal vessels, and reduced trophoblast proliferation.

Show evidence (2 references)

PMID:15639195 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Although no consistent anomalies were identified in affected male embryos themselves, the labyrinth layer of the fetal placenta was always thinner, with fewer fetal vessels and decreased proliferation of labyrinth trophoblast cells."

Several mouse alleles show a placental structural phenotype associated with prenatal lethality; it does not establish the cause of every male loss or a human placental lesion.

PMID:17028112 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Further, affected placentas from mutant Nsdhl(Bpa-8H) male embryos demonstrate markedly decreased or no Ptch1-lacZ staining and no migration of Ihh expressing cells into the developing placenta."

Placental reporter and cellular-distribution observations implicate Hedgehog signaling in this mouse allele.

Increased Receptor Lysosomal Trafficking

Mechanism confidence: Provisional

NSDHL depletion in experimental cell systems reduces EGFR recycling and shifts receptor-associated signals toward late endosomal and lysosomal compartments. The assays use knockdown and model cells, not direct measurements in human CHILD lesions.

Experimental models

NSDHL-depleted cell models of receptor trafficking CELL LINE NSDHL depletion shifts receptor-associated signals away from recycling endosomes and toward late endosomal compartments.

Downstream

Reduced EGFR Signaling Accelerated receptor degradation can reduce the signaling receptor pool; mouse-skin observations support reduced pathway activation in NSDHL-null regions.

Show evidence (2 references)

PMID:23125191 SUPPORT DIRECT PRIMARY RESULT In Vitro

"In contrast, depletion of either SC4MOL or NSDHL significantly reduced the amount of fluorescently labeled EGFR ... associated with RAB11-positive recycling endosomes after 30 minutes of EGF stimulation."

NSDHL knockdown in experimental cells reduced receptor localization to recycling endosomes; this is not a patient-tissue result.

PMID:23125191 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Conversely, SC4MOL and NSDHL-deficient cells showed an accelerated concentration of internalized fluorescently labeled EGF in RAB7-positive ... or EGFR in LAMP1-positive late endosomes"

Experimental depletion shifts receptor-associated signals toward late endosomal compartments.

Reduced EGFR Signaling

Mechanism confidence: Provisional

NSDHL-null patches of mouse skin show reduced activated EGFR, ERK, and AKT signals with reduced proliferation and loricrin expression. These model observations suggest altered epidermal growth and differentiation, but do not demonstrate the same signaling state in patient skin.

Animal models

Bare patches and striated mice (Nsdhl mutant) Mouse partially recapitulates NSDHL-null mouse skin has reduced activated EGFR and downstream signals with reduced proliferation.

Show evidence (2 references)

PMID:23125191 SUPPORT DIRECT PRIMARY RESULT Model Organism

"The reduced intracellular EGFR staining was accompanied by a marked loss of phosphorylated (activated) Y1173-EGFR ... signal in the NSDHL-null areas."

NSDHL-null patches of mouse skin had reduced activated EGFR; the original sentence also reports reduced ERK and AKT phosphorylation.

PMID:23125191 SUPPORT DIRECT PRIMARY RESULT Model Organism

"The NSDHL-null areas of the skin also exhibited significantly reduced proliferation, as determined by Ki-67 ... expression and in vivo BrdU incorporation"

Mouse skin proliferation was reduced, so human hyperkeratosis must not be generalized into a universal increase in cellular proliferation.

Impaired Anagen Hair Growth

Mechanism confidence: Provisional

Bpa1H mouse skin has impaired postnatal anagen progression despite apparently normal early follicle morphology. In treated CHILD patients, improvement of the skin lesions did not restore hair growth. A specific Hedgehog-mediated explanation for the human hair phenotype remains an inference.

Animal models

Bare patches and striated mice (Nsdhl mutant) Mouse partially recapitulates Mutant mouse skin has impaired anagen growth despite apparently normal early follicle morphology.

Downstream

Alopecia of affected skin Defective follicle growth in Nsdhl mouse skin is consistent with the human failure of hair growth; the intervening human pathway has not been demonstrated.

Show evidence (2 references)

PMID:19631568 SUPPORT DIRECT PRIMARY RESULT Model Organism

"The mutant follicles were smaller and shorter than adjacent WT follicles and lacked hair shafts, consistent with defective anagen hair growth."

Mouse mutant skin shows defective postnatal anagen growth; initial P2 follicle morphology was not grossly abnormal.

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"By 6 months, treated skin largely normalized, but did not grow hair"

Skin improvement and hair growth were distinct outcomes in two treated patients.

✶

Histopathology

Psoriasiform hyperkeratosis and acanthosis with loss of the granular layer

Lesional skin shows marked hyperkeratosis and acanthosis with absence of the granular layer, together with foam cells in the dermis. This is the routine light-microscopic picture, and it reverses on effective pathogenesis-based therapy: after three months of topical cholesterol plus lovastatin the epidermis was largely normal with a prominent granular layer and orthokeratotic scale.

Show evidence (1 reference)

PMID:21753784 SUPPORT Human Clinical

"Baseline biopsy sections of skin lesions from both patients prior to treatment showed marked hyperkeratosis and acanthosis with absence of the granular layer and dermal foam cells"

Reports the light-microscopic findings in lesional skin from both patients, including the dermal foam cells.

Verruciform xanthoma-like change in the CHILD nevus

Verruciform xanthoma-like histology can occur in the CHILD nevus, together with psoriasiform changes. It is not specific enough to establish the diagnosis by itself. A prominent vulvar and inner-thigh lesion required debulking in one patient in the topical-treatment report.

Show evidence (3 references)

PMID:7640190 SUPPORT REVIEW SYNTHESIS Other

"The associated CHILD nevus shows unique features such as a diffuse form of lateralization, ptychotropism, and microscopic changes of verruciform xanthoma."

The review describes verruciform xanthoma-like changes in CHILD nevi; the finding is not diagnostic by itself.

PMID:16776722 SUPPORT Human Clinical

"The histology shared many features with verruciform xanthoma."

Independent case confirmation of the verruciform xanthoma resemblance.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"this is a nonspecific histopathologic finding that can be seen in other entities but may help distinguish CHILD nevi from other psoriasiform lesions on histopathology."

GeneReviews explicitly limits the specificity of verruciform xanthoma-like histology.

Abnormal lamellar granules on electron microscopy

Ultrastructurally the lesion is a lipid secretory failure. Vesicular structures appear in the intercellular spaces of the stratum corneum and vacuoles in the upper prickle cell layer, some recognizable as abnormal lamellar granules, with large vacuoles inside the foamy cells of the papillary dermis. This is the electron-microscopic counterpart of the lamellar body secretory defect modelled in the pathophysiology, observed in a separate patient and laboratory from the treatment study.

Show evidence (1 reference)

PMID:16776722 SUPPORT Human Clinical

"These findings suggested that abnormal lipid metabolism involving lamellar granules may be responsible to the skin lesion of CHILD syndrome."

States the authors' interpretation linking the ultrastructural finding to the lipid-metabolic lesion, preserving the hedged form they used.

Gastrointestinal mucosal xanthomatous infiltrates

Upper gastrointestinal biopsies in a molecularly confirmed adult showed finely vacuolated xanthoma cells in the lamina propria, positive for the macrophage marker CD163.

Show evidence (2 references)

PMID:34957706 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"An esophagogastroduodenoscopy revealed multiple whitish plaques in the proximal duodenum, stomach and distal oesophagus ... Biopsies of these areas showed similar xanthoma cells with finely vacuolated cytoplasm in the lamina propria"

A molecularly confirmed adult had gastrointestinal mucosal xanthomas demonstrated by endoscopy and biopsy.

PMID:34957706 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"These cells were positive for CD163 stain ... confirming their macrophage lineage and the diagnosis of gastrointestinal xanthomatosis."

Immunostaining identifies the mucosal xanthoma cells as macrophages.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

Cardiovascular 1

Cardiac septal defect Abnormal cardiac septum morphology HP:0001671

Coarse binding: source unspecified

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Heart defects include septal defects"

The source supports a septal defect without identifying its chamber location.

PMID:11907515 SUPPORT DIRECT BACKGROUND Other

"Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney."

The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.

Ear 1

Sensorineural hearing loss Sensorineural hearing impairment HP:0000407

Show evidence (1 reference)

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"The patient also had neurosensory deafness of the right ear and severe lumbar scoliosis."

The primary case report establishes the sensorineural subtype and laterality for this individual.

Eye 1

Optic atrophy HP:0000648

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Bilateral optic atrophy has been reported in one individual"

The source establishes a reported finding, not a population frequency.

Genitourinary 2

Hydronephrosis HP:0000126

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Renal manifestations range from unilateral hydronephrosis to renal agenesis. The frequency of these is unknown."

GeneReviews identifies these renal findings while explicitly leaving their frequencies unknown.

PMID:11907515 SUPPORT DIRECT BACKGROUND Other

"Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney."

The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.

Renal agenesis HP:0000104

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Renal manifestations range from unilateral hydronephrosis to renal agenesis. The frequency of these is unknown."

GeneReviews identifies these renal findings while explicitly leaving their frequencies unknown.

PMID:11907515 SUPPORT DIRECT BACKGROUND Other

"Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney."

The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.

Integument 3

Ichthyosiform nevus Epidermal nevus HP:0010816

Show evidence (3 references)

PMID:21290788 SUPPORT REVIEW SYNTHESIS Other

"CHILD syndrome is characterized by unilateral distribution of ichthyosiform skin lesions and ipsilateral limb defects that range from shortening of the metacarpals and phalanges to absence of the entire limb."

GeneReviews names the unilateral ichthyosiform lesion as a defining feature.

PMID:24060582 SUPPORT REVIEW SYNTHESIS Other

"The CHILD syndrome skin is characterized by plaques topped by waxy scales and a variety of developmental defects in extracutaneous tissues, particularly limb hypoplasia or aplasia."

Describes the characteristic morphology of the plaques.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Most of the skin lesions improve spontaneously, but some can cause lifelong morbidity. Lesions in the intertriginous areas tend to be more persistent; this is termed ptychotropism"

GeneReviews describes the variable natural history and persistence in body folds.

Onychodystrophy and periungual hyperkeratosis Nail dystrophy HP:0008404

Show evidence (2 references)

PMID:21290788 SUPPORT REVIEW SYNTHESIS Other

"Onychodystrophy and periungual hyperkeratosis are common."

GeneReviews describes both findings as common without providing a denominator for a numerical frequency.

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"She has improved digital mobility, but little improvement in onychodystrophy, likely reflecting the inability of the compound to penetrate the nail."

One treated patient had persistent nail dystrophy; impaired penetration was the authors' proposed explanation.

Alopecia of affected skin HP:0001596

Show evidence (1 reference)

PMID:21753784 SUPPORT Human Clinical

"By 6 months, treated skin largely normalized, but did not grow hair"

Reports the persistence of alopecia despite otherwise successful treatment.

Limbs 4

Ipsilateral limb hypoplasia or aplasia Aplasia/hypoplasia involving bones of the extremities HP:0045060

Show evidence (1 reference)

PMID:21290788 SUPPORT REVIEW SYNTHESIS Other

"unilateral distribution of ichthyosiform skin lesions and ipsilateral limb defects that range from shortening of the metacarpals and phalanges to absence of the entire limb"

GeneReviews states the ipsilateral limb defect and its severity range as a defining characteristic.

Oligodactyly HP:0012165

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Oligodactyly can be seen; polydactyly and syndactyly have been rarely reported."

GeneReviews describes reduced digit number and occasional additional or fused digits without a numerical denominator.

Polydactyly HP:0010442

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Oligodactyly can be seen; polydactyly and syndactyly have been rarely reported."

GeneReviews describes reduced digit number and occasional additional or fused digits without a numerical denominator.

Syndactyly HP:0001159

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Oligodactyly can be seen; polydactyly and syndactyly have been rarely reported."

GeneReviews describes reduced digit number and occasional additional or fused digits without a numerical denominator.

Musculoskeletal 3

Stippled epiphyseal calcification Stippled chondral calcification HP:0002764

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Unilateral punctate epiphyseal calcifications (chondrodysplasia punctata) in the pelvis, ribs, vertebrae, and extremities have been reported and are usually seen in the affected limb or body part."

GeneReviews describes the distribution of punctate calcifications in CHILD syndrome.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"In one child, the punctate calcifications were reported to have disappeared completely by age two years ... it is not known whether stippling always disappears."

The review limits evidence for disappearance to one reported child.

Scoliosis HP:0002650

Show evidence (1 reference)

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"The patient also had neurosensory deafness of the right ear and severe lumbar scoliosis."

The primary report directly documents scoliosis and hearing loss in a molecularly confirmed patient.

Joint contracture HP:0034392

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Joint contractures are reported. Oligodactyly can be seen; polydactyly and syndactyly have been rarely reported."

GeneReviews lists contractures among the limb findings.

Nervous System 3

Type II lissencephaly HP:0007260

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"CNS anomalies include unilateral hypoplasia or underdevelopment of the brain, lissencephaly type II, and cerebellar malformation"

The CHILD-specific clinical section lists these structural brain abnormalities; they are not imported from the separate CK syndrome section.

PMID:11907515 SUPPORT DIRECT BACKGROUND Other

"Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney."

The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.

Cerebellar malformation Abnormal cerebellum morphology HP:0001317

Coarse binding: source unspecified

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"CNS anomalies include unilateral hypoplasia or underdevelopment of the brain, lissencephaly type II, and cerebellar malformation"

The CHILD-specific clinical section lists these structural brain abnormalities; they are not imported from the separate CK syndrome section.

PMID:11907515 SUPPORT DIRECT BACKGROUND Other

"Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney."

The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.

Unilateral vocal cord paralysis HP:0008757

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Ipsilateral vocal cord paralysis and liver lobe and spleen hypertrophy have been reported"

The source lists ipsilateral vocal cord paralysis as an additional finding.

Respiratory 1

Pulmonary hypoplasia HP:0002089

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Lung hypoplasia has been observed in several individuals ... and can cause respiratory compromise and death"

GeneReviews identifies the specific pulmonary malformation and its potential severity.

PMID:11907515 SUPPORT DIRECT BACKGROUND Other

"Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney."

The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.

Growth 1

Ipsilateral body hypoplasia Asymmetric growth HP:0100555

Show evidence (2 references)

PMID:10710235 SUPPORT Human Clinical

"an inflammatory nevus with striking lateralization and strict midline demarcation, as well as ipsilateral hypoplasia of the body"

States the ipsilateral hypoplasia of the body, which is the asymmetric growth this term describes.

PMID:7408908 SUPPORT Human Clinical

"In addition, ipsilateral hypoplasia of other parts of the skeleton, as well as defects of the brain and the viscera are found."

Extends the ipsilateral hypoplasia beyond the limbs to the rest of the skeleton and the viscera.

Other 3

Strict midline demarcation of skin lesions

Show evidence (3 references)

PMID:10710235 SUPPORT Human Clinical

"an inflammatory nevus with striking lateralization and strict midline demarcation, as well as ipsilateral hypoplasia of the body"

States the midline demarcation of the nevus, which is the claim this phenotype makes.

PMID:7408908 SUPPORT Human Clinical

"The syndrome is characterized by unilateral erythema and scaling, with a distinct demarcation in the middle of the trunk."

The original delineation locates the demarcation anatomically, at the middle of the trunk.

PMID:11907515 SUPPORT Human Clinical

"A symmetric distribution of this nevus can exceptionally be seen in patients with CHILD syndrome, and this bilateral involvement should not mislead the clinician to any other diagnosis."

Qualifies rather than supports the lateralization claim, documenting the exception that makes midline demarcation typical but not obligatory.

Unilateral brain hypoplasia

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"CNS anomalies include unilateral hypoplasia or underdevelopment of the brain, lissencephaly type II, and cerebellar malformation"

The CHILD-specific clinical section lists these structural brain abnormalities; they are not imported from the separate CK syndrome section.

PMID:11907515 SUPPORT DIRECT BACKGROUND Other

"Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney."

The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.

Gastrointestinal mucosal xanthomas

Show evidence (1 reference)

PMID:34957706 SUPPORT DIRECT PRIMARY RESULT Human Clinical

A molecularly confirmed adult had gastrointestinal mucosal xanthomas demonstrated by endoscopy and biopsy.

🧬

Genetic Associations

NSDHL

Gene: NSDHL hgnc:13398 gene page relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (4 references)

PMID:10710235 SUPPORT Human Clinical

"SSCA and genomic sequence analysis of NSDHL identified in 6 patients with CHILD syndrome, including one boy as well as a mother and her daughter, mutations potentially impairing protein function."

Establishes NSDHL variants as the molecular cause in a patient series.

PMID:21290788 SUPPORT REVIEW SYNTHESIS Other

"The diagnosis of CHILD syndrome is established in a female proband with a heterozygous NSDHL pathogenic variant identified by molecular genetic testing that results in loss of functional decarboxylating sterol-4-alpha-carboxylate 3-dehydrogenase, the protein encoded by NSDHL."

GeneReviews states the diagnostic criterion and the loss-of-function consequence at the protein level.

PMID:21129721 SUPPORT DIRECT PRIMARY RESULT In Vitro

"These two mutations, which alter protein folding, show temperature-sensitive protein stability and complementation in Erg26-deficient yeast."

The original CK syndrome study demonstrates residual, temperature-sensitive function of its two studied alleles, supporting the distinction from severe CHILD loss of function.

+ 1 more reference

💊

Medical Actions

Topical Cholesterol plus Statin (Pathogenesis-Based Therapy)

Action: Pharmacotherapy NCIT:C15986

Agent: cholesterol CHEBI:16113 lovastatin CHEBI:40303 simvastatin CHEBI:9150

Platform: Small molecule

Topical lovastatin or simvastatin combined with cholesterol has improved cutaneous lesions in uncontrolled reports. In the original two-patient study, 10% cholesterol alone produced no improvement over three months, followed by substantial improvement with 2% lovastatin/2% cholesterol. There was no statin-only arm, so this sequence does not establish that cholesterol supplementation is required. Later reports describe benefit from statin monotherapy. Skin improvement does not establish correction of congenital skeletal defects, and long-term comparative efficacy and safety remain uncertain.

Mechanism Target:

RESTORES Reduced Cholesterol Availability — The cholesterol component supplies the pathway end product; tissue-specific target engagement was not isolated from the effects of the statin in the clinical report.

Show evidence (1 reference)

PMID:21753784 SUPPORT INDIRECT Human Clinical

"On the basis of the putative pathogenic role of both pathway-product deficiency of cholesterol and accumulation of toxic metabolic intermediates, we assessed the efficacy of combined therapy with lovastatin and cholesterol."

The authors state the dual treatment rationale as putative. The combined intervention does not isolate restoration of cholesterol from suppression of precursor formation.

INHIBITS C4-Methylsterol Accumulation — Upstream statin inhibition is intended to reduce precursor production; clinical response to the combination is consistent with this rationale but does not quantify precursor clearance.

Show evidence (1 reference)

PMID:21753784 SUPPORT INDIRECT Human Clinical

The authors state the dual treatment rationale as putative. The combined intervention does not isolate restoration of cholesterol from suppression of precursor formation.

Show evidence (6 references)

PMID:21753784 SUPPORT Human Clinical

"Topical treatment with lovastatin/cholesterol (but not cholesterol alone) virtually cleared skin lesions by 3 months, accompanied by histological and ultrastructural normalization of epidermal structure and lipid secretion."

Cholesterol alone did not improve the lesions in this two-patient sequence; there was no statin-only comparison to establish that the combination is required.

PMID:25845514 SUPPORT Human Clinical

"We report the case of a 10-year-old girl treated with topical simvastatin and cholesterol ointment, after which her skin lesions significantly improved within the first 30 days of treatment."

Independent case replication using simvastatin in place of lovastatin.

PMID:31365666 SUPPORT Human Clinical

"The authors report a 2-month-old patient presenting with typical features of CHILD syndrome that was treated with a topical solution containing cholesterol and lovastatin, with complete clearance of her CHILD nevus."

An additional infant case had clearance of the nevus with the combination.

+ 3 more references

Topical Simvastatin Monotherapy

Action: Pharmacotherapy NCIT:C15986

Agent: simvastatin CHEBI:9150

Platform: Small molecule

Uncontrolled reports describe improvement with topical simvastatin without added cholesterol. In an infant treated with 2% ointment twice daily, improvement appeared by three weeks and the skin largely normalized by six weeks, with maintenance treatment over ten months. A later 5% report describes variable responses by site and recurrent lesions; it follows the previously reported p.Gly44Ser patient rather than adding an independent genotype case. Comparative efficacy and long-term safety are not established.

Show evidence (6 references)

PMID:29687057 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"After obtaining informed consent from her father, we began treatment with twice-daily topical simvastatin 2% ointment"

The primary case used simvastatin monotherapy.

PMID:29687057 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Decreased inflammation, skin thickening, and scaling were noted as early as 3 weeks. By 6 weeks, the treated skin largely and dramatically normalized with a discrete postinflammatory hypopigmentation remaining"

Clinical results describe improvement by three weeks and near-normalization at six weeks.

PMID:29687057 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"No reoccurrence was observed after 10 months of maintenance topical treatment"

Continued maintenance accompanied the reported sustained response.

+ 3 more references

Topical Ketoconazole

Action: Pharmacotherapy NCIT:C15986

Agent: ketoconazole CHEBI:47519

Platform: Small molecule

Off-label topical 2% ketoconazole has improved cutaneous lesions in individual reports. In one adult using it twice daily, itch improved after two days, erythema and scaling improved by day seven, and lesions were substantially improved by day 40. DLQI decreased from 3 to 1, with no apparent adverse effects during two and a half months of follow-up. This uncontrolled observation does not establish equivalence to statins or durable remission after stopping treatment.

Show evidence (5 references)

PMID:39565229 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Institutional approval was obtained for the off-label use of 2% ketoconazole cream. The pre-treatment Dermatology Life Quality Index (DLQI) score was 3 out of 30."

The adult report specifies the off-label formulation and baseline quality-of-life score.

PMID:39565229 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"The itching improved after 2 days of treatment. At 7 days after the start of the treatment, the area of erythema was unchanged, but the desquamation had generally disappeared and the redness of the erythema had improved"

The clinical endpoints distinguish symptom improvement from the unchanged area at one week.

PMID:39565229 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"At 40 days of treatment, the skin lesions had significantly improved, with only minimal pigmentation."

The report describes substantial improvement by day 40.

+ 2 more references

Symptomatic Topical Care

Action: Supportive Care NCIT:C15747

Platform: Other

Lactic acid preparations can reduce itching and urea creams can help dry skin. Emollients, keratolytics and other topical anti-inflammatory treatments have had variable benefit in individual reports. GeneReviews also describes poorly tolerated or inconsistent responses to oral etretinate. These observations do not establish comparative efficacy.

Show evidence (3 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Lactic acid 12% creams or lotions for itching"

GeneReviews lists symptomatic topical care for itch.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Urea creams for dry skin"

GeneReviews lists urea for dryness.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Oral aromatic retinoids (etretinate) may ameliorate cutaneous symptoms; however, this drug is often poorly tolerated ... & does not prove effective in every person."

The review qualifies both tolerability and consistency of reported etretinate benefit.

Skin Grafting from the Unaffected Side

Action: Skin Transplantation NCIT:C15325

Platform: Surgery

Grafting skin from the unaffected contralateral region has been successful in an individual report. GeneReviews also describes recurrence within eight months after dermabrasion; these sparse reports do not establish comparative surgical effectiveness.

Mechanism Target:

BYPASSES X-Inactivation-Dependent NSDHL Expression Mosaicism — Grafting replaces mutant-expressing epidermis with wild-type-expressing epidermis, bypassing rather than correcting the mosaic distribution.

Show evidence (1 reference)

PMID:21290788 SUPPORT REVIEW SYNTHESIS Other

"Treatment of an inflammatory nevus by grafting skin obtained from a contralateral unaffected region has been successful."

Reports the intervention and its dependence on an unaffected-side donor site, which is what makes it a mosaic-bypassing strategy.

Show evidence (2 references)

PMID:21290788 SUPPORT REVIEW SYNTHESIS Other

"Treatment of an inflammatory nevus by grafting skin obtained from a contralateral unaffected region has been successful."

GeneReviews records grafting as an effective option for a localized inflammatory nevus.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Removal by dermabrasion was reported; however, it recurred w/in 8 mos."

GeneReviews records recurrence after dermabrasion as a limitation of that separate procedure.

Orthopedic and Rehabilitative Management of the Limb and Spine Defects

Action: Orthopedic Surgical Procedure NCIT:C16186

Platform: Surgery

Braces and corrective surgery are used for scoliosis and joint contractures. Prosthetic fitting and rehabilitation may be needed for severe limb reduction. In one reported patient, skin improvement permitted use of a prosthesis; this was a functional benefit without reversal of the congenital skeletal defect.

Show evidence (2 references)

PMID:21290788 SUPPORT REVIEW SYNTHESIS Other

"Scoliosis and joint contractures are treated with braces and/or corrective surgery."

GeneReviews states the orthopedic management of the axial and joint deformities.

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Patient #1, now more than 1 year on therapy, uses the medication twice weekly with good control and is able to wear her prosthesis."

Improved skin tolerance enabled prosthesis use in this patient.

Initial Multisystem Assessment and Surveillance

Action: Supportive Care NCIT:C15747

Platform: Other

GeneReviews recommends initial assessment of cutaneous, skeletal, neurologic, cardiac, pulmonary and renal involvement, including echocardiography, chest imaging and abdominal/pelvic ultrasound. Developmental assessment and neurologic evaluation address CNS manifestations. Subsequent monitoring for skin lesions, scoliosis, contractures and neurologic, cardiac or renal manifestations is annual or as needed, with relevant specialist care. These recommendations reflect the GeneReviews authors' experience rather than a formal clinical practice guideline.

Show evidence (5 references)

PMID:21290788 SUPPORT REVIEW SYNTHESIS Other

"In CHILD syndrome, monitor for new cutaneous lesions, musculoskeletal deformities such as scoliosis and joint contractures, and neurologic, cardiac, and/or kidney manifestations annually or as needed."

GeneReviews states the surveillance schedule and the organ systems it covers.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Cardiac Echocardiogram Evaluate for congenital heart disease."

The initial-evaluation table recommends echocardiography.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Pulmonary Chest imaging Evaluate for lung hypoplasia."

The initial-evaluation table specifically addresses lung hypoplasia.

+ 2 more references

Genetic Counseling

Action: Genetic Counseling NCIT:C15240

Platform: Other

Counseling addresses X-linked inheritance, a 50% transmission probability for a heterozygous mother, variable expression in females and the effect of usual hemizygous male lethality on live-born ratios. Once a familial pathogenic variant is identified, testing of relatives and prenatal or preimplantation testing are possible. A VUS alone does not establish a molecular diagnosis or a variant-specific recurrence risk.

Show evidence (2 references)

PMID:21290788 SUPPORT REVIEW SYNTHESIS Other

"Once the NSDHL pathogenic variant has been identified in a family member with an NSDHL-related disorder, prenatal and preimplantation genetic testing are possible."

States the reproductive testing options that counseling is built around.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"The chance of transmitting the pathogenic variant in each pregnancy is 50%."

GeneReviews states the transmission probability for a heterozygous mother.

🔬

Biochemical Markers

Methylsterol accumulation in affected tissue (INCREASED)

Show evidence (2 references)

PMID:24060582 SUPPORT REVIEW SYNTHESIS Other

"which leads to inhibition of cholesterol synthesis and accumulation of toxic metabolic intermediates in affected tissues"

States the accumulation of intermediates and localizes it to affected tissues rather than the circulation.

PMID:10369263 SUPPORT Model Organism

"Quantitative analysis of sterols from tissues of affected Bpa mice support a role for Nsdhl in cholesterol biosynthesis."

Reports the tissue sterol measurements in the mouse counterpart of the disorder.

🔬

Diagnosis

NSDHL molecular genetic testing

Diagnosis is supported by characteristic findings and a pathogenic or likely pathogenic NSDHL variant. Sequence analysis detects many coding and splice variants, while exon-level deletion/duplication analysis is needed for copy-number variants that conventional sequencing can miss. A variant of uncertain significance neither establishes nor excludes the diagnosis. Rare mosaic males and mild females require clinical and molecular interpretation rather than exclusion by sex or by absence of a severe limb defect. Optical genome mapping has been reported in a mixed cohort of incontinentia pigmenti and CHILD syndrome; this does not establish a general diagnostic yield for CHILD syndrome.

Genetic Testing NCIT:C15709

Show evidence (4 references)

PMID:21290788 SUPPORT REVIEW SYNTHESIS Other

GeneReviews states the diagnostic criterion.

PMID:29341259 SUPPORT Human Clinical

"Multiple exons deletions or microdeletion was not rare in CHILD syndrome. Classical Sanger sequencing may not be useful enough to find all kinds of mutations. Next-generation sequencing may be more effective."

States the assay blind spot directly, and the same report supplies the worked example, a large deletion of NSDHL exons 3 and 4.

PMID:41625319 SUPPORT Human Clinical

"The identified structural variants consisted of deletions of varying sizes in the Xq28 cytoband, encompassing regions that contain exons."

The abstract reports structural variants in a mixed incontinentia pigmenti/CHILD cohort. It does not assign every deletion to NSDHL or establish a CHILD-specific diagnostic yield.

+ 1 more reference

Sterol profiling of skin flakes and plasma

Sterol profiling of affected skin can support biochemical interpretation of an NSDHL variant. In one p.Gly44Ser case, skin-flake methyl-, carboxy- and keto-sterol abnormalities supported reclassification from uncertain significance to likely pathogenic. An abnormal methylsterol was also detected in plasma in that patient. Serum profiles can be near normal, so a normal systemic result does not exclude the disorder.

Diagnostic Procedure NCIT:C18020

Show evidence (3 references)

PMID:33139364 SUPPORT Human Clinical

"Sterol analysis from skin flakes revealed increased levels of a mono 4-alpha methyl sterol also seen in plasma as well as the presence of 4-alpha-carboxy-4-methyl-cholest-8(9)-en-3beta-ol and several keto-sterols, which are usually below the limit of detection. This sterol pattern is consistent..."

Reports the sterol pattern and its interpretation as evidence of the enzymatic block.

PMID:33139364 SUPPORT Human Clinical

"On this basis, this variant has been reclassified as likely pathogenic."

Documents the concrete diagnostic use of the sterol result, resolving a variant of uncertain significance.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Serum concentrations of methylsterol and cholesterol are almost always normal in individuals with CHILD syndrome and CK syndrome."

GeneReviews limits the usefulness of normal serum sterols for excluding these disorders.

📈

Progression

Postnatal improvement of cutaneous lesions

Cutaneous lesions can improve with age, but intertriginous lesions may persist and new lesions can arise later, including at sites of injury.

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Most of the skin lesions improve spontaneously, but some can cause lifelong morbidity. Lesions in the intertriginous areas tend to be more persistent; this is termed ptychotropism"

GeneReviews describes the human cutaneous course.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"Ichthyosiform skin lesions can develop after infancy at sites of injury such as a surgical wound."

Lesions can also appear after early development.

Survival into adulthood

Life span in females is not well characterized. Adults with a wide range of disease severity have been reported, including an individual diagnosed at age 82; that observation does not establish a normal population life expectancy. Pulmonary hypoplasia can cause early respiratory compromise and death.

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"It is unknown whether life span in females with CHILD syndrome is abnormal."

GeneReviews explicitly states uncertainty about life expectancy.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"CHILD syndrome was reported with phenotypes ranging from mild to severe in three different generations, with the oldest reported individual clinically and molecularly diagnosed at age 82 years"

The source documents survival to old age in a family, not a population survival estimate.

📊

Prevalence

Published cases summarized in GeneReviews, September 2024

Cases In Literature

GeneReviews reported more than 60 individuals in its September 2024 update and stated that prevalence is unknown. This historical literature count is neither a current total nor a population prevalence estimate.

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf SUPPORT DIRECT REVIEW SYNTHESIS Other

"The prevalence of CHILD syndrome is unknown; more than 60 individuals have been reported to date."

The source reports a literature count while explicitly stating that population prevalence is unknown.

🔀

Differential Diagnoses

Conditions with similar clinical presentations that must be differentiated from CHILD Syndrome:

X-linked chondrodysplasia punctata 2 (Conradi-Hunermann-Happle syndrome) MONDO:0020603

Overlapping Features EBP-related X-linked chondrodysplasia punctata 2 is a distinct sterol-biosynthesis disorder with overlapping ichthyotic skin and skeletal findings. An early patient described clinically as CHILD syndrome had an EBP nonsense variant and a CDPX2 sterol profile. Current GeneReviews places EBP-related CDPX2 in the differential of NSDHL-related CHILD syndrome; the historical label does not establish EBP as a second causative gene for this entry.

Distinguishing Features

CDPX2 commonly has bilateral asymmetric skin and skeletal involvement. CHILD often has sharper lateralization, but bilateral CHILD presentations mean distribution alone is not definitive.
CDPX2 is caused by EBP variants affecting sterol delta8-delta7 isomerization, a different enzymatic step from NSDHL-dependent C4-demethylation.
CDPX2 carries a plasma sterol signature of raised 8-dehydrocholesterol and 8(9)-cholestenol that NSDHL-related CHILD syndrome does not

Show evidence (2 references)

PMID:10710235 SUPPORT Human Clinical

"EBP was unaffected in the patients analyzed by us demonstrating that CHILD syndrome and CDPX2 are not caused by allelic mutations."

Establishes that in this cohort the two are genetically distinct despite their shared pathway and overlapping clinical picture.

PMID:10710233 SUPPORT Human Clinical

"although the skeletal defects and skin lesions in CDPX2 are bilateral and asymmetric"

States the clinical distinction in lesion distribution that separates the two on examination.

Inflammatory linear verrucous epidermal nevus (ILVEN) Not Yet Curated MONDO:0019318

Overlapping Features ILVEN can resemble the inflammatory verrucous CHILD nevus. A reported boy initially suspected to have CHILD syndrome was diagnosed with severe ILVEN despite ipsilateral contracture and short stature. Distribution and extracutaneous findings therefore require interpretation together with molecular and biochemical testing.

Distinguishing Features

A pathogenic NSDHL variant and the corresponding sterol-biosynthesis abnormality support CHILD syndrome; negative or incomplete testing alone does not prove ILVEN.
Both ILVEN and CHILD lesions can follow Blaschko lines, so that pattern alone does not distinguish them.
ILVEN lacks the ipsilateral skeletal hypoplasia or aplasia of CHILD syndrome, though an ipsilateral limb contracture has been reported in ILVEN, so limb involvement alone does not settle it
CHILD syndrome predominantly affects females, but rare mosaic males are reported; male sex alone does not exclude it.

Show evidence (2 references)

PMID:39953436 SUPPORT Human Clinical

"Initially, we suspected this may be a rare case of CHILD syndrome in a boy. However, after further investigation, we confirmed the diagnosis as a severe form of ILVEN."

A worked case of the differential actually being made, with CHILD syndrome as the initial working diagnosis and ILVEN as the resolution.

PMID:39953436 SUPPORT Human Clinical

"He also had an associated contracture in the ipsilateral limb and short stature."

Documents that the ILVEN case carried ipsilateral limb findings too, which is why extracutaneous involvement does not by itself distinguish the two.

CK syndrome

Overlapping Features CK syndrome is an allelic NSDHL disorder associated with hypomorphic variants. Affected males typically have intellectual disability, behavioral problems, infantile seizures, cortical malformations and microcephaly. This differs from the predominant cutaneous and limb phenotype of CHILD syndrome, although both disorders can have CNS manifestations.

Distinguishing Features

CK syndrome typically affects males with hypomorphic NSDHL variants; CHILD syndrome predominantly affects heterozygous females, with rare mosaic males.
CK syndrome is dominated by cognitive impairment, seizures, and cortical malformation, whereas intellect is usually normal in CHILD syndrome
CK syndrome lacks the lateralized ichthyosiform nevus and ipsilateral limb defects

Show evidence (1 reference)

PMID:21290788 SUPPORT REVIEW SYNTHESIS Other

"The diagnosis of CK syndrome is established in a male proband with a hemizygous NSDHL hypomorphic pathogenic variant identified by molecular genetic testing that results in partial loss of functional decarboxylating sterol-4-alpha-carboxylate 3-dehydrogenase."

States the allelic relationship and the partial-loss-of-function basis that separates CK syndrome from CHILD syndrome.

🧫

Experimental Models

Heterologous expression of NSDHL missense mutants CELL_LINE

Heterologous expression assays examined thirteen disease-associated NSDHL missense variants and one deletion. Protein abundance was reduced for all tested variants and partly increased for selected variants at lower temperature or with glycerol. The abstract also implicates heat shock proteins in optimal expression, potentially through protein synthesis. These findings do not distinguish instability from impaired synthesis for every variant or demonstrate restored enzyme activity after abundance rescue.

Publication

PMID:40222685

Pathograph links

NSDHL Loss of Function measures fidelity: moderate observes: molecular Measures variant-associated reductions in NSDHL protein abundance and partial abundance rescue in selected conditions.

Limitations: Heterologous overexpression in cultured cells does not report on endogenous expression in keratinocytes or on the mosaic tissue context, and a temperature or glycerol rescue in culture is not evidence that any clinically usable chaperone therapy exists.

Readouts

NSDHL mutant protein expression level

Direction: DECREASED

Interpretation: Steady-state abundance is lower for the tested variants; the assay does not by itself distinguish reduced synthesis from faster degradation.

Show evidence (1 reference)

PMID:40222685 SUPPORT In Vitro

"Here we show that protein expression levels were low for all mutants, but some could be rescued by a lower temperature (30°C vs. 37°C) and/or the chemical chaperone glycerol."

Reports the expression measurement behind this readout.

Show evidence (1 reference)

PMID:40222685 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Here we show that protein expression levels were low for all mutants, but some could be rescued by a lower temperature (30°C vs. 37°C) and/or the chemical chaperone glycerol."

The measured endpoint is protein abundance; neither catalytic rescue nor clinical benefit follows from it.

Show evidence (1 reference)

PMID:40222685 SUPPORT In Vitro

"We examined 13 missense mutations and one deletion mutation in the cholesterol synthesis enzyme NSDHL (NAD(P) Dependent Steroid Dehydrogenase-Like), known to cause the X-linked developmental disorders CHILD (congenital hemidysplasia with ichthyosiform erythroderma and limb defects) syndrome and..."

States that the alleles assayed in this system are the ones that cause CHILD syndrome, which is the model-level relevance claim.

Paired patient skin keratinocyte and fibroblast cultures PRIMARY_CELL_CULTURE

Cultures from affected and clinically unaffected skin of one heterozygous patient were compared by genomic sequencing and RT-PCR. Both genomic alleles were present, while expression differed by site and cell type.

Publication

PMID:21753784

Pathograph links

X-Inactivation-Dependent NSDHL Expression Mosaicism measures fidelity: moderate observes: cellular Patient-derived cultures measure side- and cell-type-specific NSDHL allele expression.

Limitations: One patient and selected cultures do not establish the embryonic origin of the midline boundary, the full tissue composition, or a longitudinal selection process.

Show evidence (2 references)

PMID:21753784 SUPPORT DIRECT PRIMARY RESULT In Vitro

Cultures from one patient showed side-specific NSDHL allele expression; this is not a longitudinal measure of cell clearance.

+ 1 more reference

Conditional-null mouse cerebellar granule-cell precursor cultures PRIMARY_CELL_CULTURE

Granule-cell precursors isolated at P4 were cultured for 48 hours with recombinant SHH and cholesterol, LDL, or ketoconazole. Proliferation, Gli1 transcription, viability, morphology, and sterol concentrations were measured separately.

Publication

PMID:25652406

Pathograph links

Impaired Hedgehog Signal Transduction perturbs fidelity: moderate observes: cellular Cholesterol supplementation largely restores the proliferative response to SHH, while LDL restores Gli1 induction under the tested conditions.

Limitations: This is a mouse neural culture, not a whole-animal treatment or a human limb/skin experiment. SHH-induced Gli1, proliferation, morphology, and viability are distinct endpoints.

Show evidence (3 references)

PMID:25652406 SUPPORT DIRECT PRIMARY RESULT In Vitro

"We replicated the granule cell precursor proliferation defect in vitro and demonstrate that it results from defective signaling by SHH."

The experiment is in cultured mouse granule-cell precursors rather than whole animals or human limb tissue.

+ 2 more references

C4-Methylsterol Accumulation perturbs fidelity: moderate observes: cellular Upstream inhibition reduces precursor accumulation and improves mutant-cell viability without restoring SHH-induced Gli1 by itself.

Limitations: Ketoconazole changes multiple sterols. Improved viability does not assign toxicity to every precursor or establish clinical efficacy in CHILD syndrome.

Show evidence (3 references)

PMID:25652406 SUPPORT DIRECT PRIMARY RESULT In Vitro

"The concentration of methylsterols was significantly higher in NsdhlΔ5/Y GCPs than Nsdhlflx5/Y GCPs (P < 0.002) in all four culture conditions."

Cultured conditional-null mouse granule-cell precursors accumulate methylsterols under the tested conditions.

+ 2 more references

NSDHL-depleted cell models of receptor trafficking CELL_LINE

Experimental NSDHL depletion in carcinoma cell systems alters EGFR endosomal handling. Nsdhl-deficient immortalized mouse embryonic fibroblasts separately show accelerated ligand-induced PDGFR loss. These systems probe receptor trafficking rather than reproducing the full CHILD phenotype.

Publication

PMID:23125191

Pathograph links

Increased Receptor Lysosomal Trafficking perturbs fidelity: moderate observes: cellular NSDHL depletion shifts receptor-associated signals away from recycling endosomes and toward late endosomal compartments.

Limitations: Cancer-cell knockdown and immortalized mouse fibroblasts differ from patient epidermis; results involving SC4MOL alone are not assigned to NSDHL.

Show evidence (3 references)

PMID:23125191 SUPPORT DIRECT PRIMARY RESULT In Vitro

NSDHL knockdown in experimental cells reduced receptor localization to recycling endosomes; this is not a patient-tissue result.

+ 2 more references

🐁

Animal Models

Bare patches and striated mice (Nsdhl mutant)

Bare patches and striated Nsdhl mice reproduce an X-linked sterol-biosynthesis defect and mosaic skin involvement. Several alleles cause prenatal male death at E10.5-E13.5, while the severe Bpa1H allele often causes earlier death. Age-related selection is measured in liver and brain; skin, placental, signaling, and hair findings require their own tissue and allele context. Patches and stripes do not reproduce the characteristic human body-half distribution.

Species

Mouse

Genotype

Nsdhl mutant alleles Bpa and Str, X-linked dominant male-lethal

Genes

NSDHL hgnc:13398

Publication

PMID:10369263

Pathograph links

NSDHL Loss of Function recapitulates fidelity: high observes: molecular Independent Bpa and Str alleles are mutations in Nsdhl, and tissue sterol analysis confirms the biosynthetic role.

Limitations: The mouse skin phenotype is patterned as patches and stripes rather than the lateralized, midline-demarcated distribution seen in humans, so the model is informative for the enzymatic lesion but not for the lateralization.

Readouts

Tissue sterol profile in affected Bpa mice

Direction: ALTERED

Interpretation: Tissue sterol profiles support the biosynthetic consequence of the genotype; they do not directly measure every mutant protein catalytic activity.

Show evidence (1 reference)

PMID:10369263 SUPPORT Model Organism

"Quantitative analysis of sterols from tissues of affected Bpa mice support a role for Nsdhl in cholesterol biosynthesis."

Reports the sterol measurement underlying this readout.

Show evidence (1 reference)

PMID:10369263 SUPPORT PRIMARY RESULT Model Organism

"Here we report mutations in one of these genes, Nsdhl, encoding an NAD(P)H steroid dehydrogenase-like protein, in two independent Bpa and three independent Str alleles."

Establishes that these mouse mutants carry lesions in the orthologous gene.

X-Inactivation-Dependent NSDHL Expression Mosaicism partially recapitulates fidelity: moderate observes: cellular Heterozygous female mice show patches of NSDHL-positive and NSDHL-negative tissue.

Limitations: Mouse patches and stripes differ from a human body-half boundary; tissue X-inactivation and selection are context-dependent.

Show evidence (1 reference)

PMID:19631568 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Heterozygous Bpa(1H) females are mosaic for NSDHL expression due to normal random X-inactivation."

The mouse model reproduces mosaic expression, while its pattern differs from human lateralization.

Age-Dependent Depletion of NSDHL-Deficient Cells partially recapitulates fidelity: moderate observes: cellular Cross-sectional mouse age groups show a higher proportion of NSDHL-positive hepatocytes with age.

Limitations: The quantitative comparison is in liver, with additional brain observations. Mutant skin remains at eight weeks; this is not evidence of longitudinal clearance in human skin.

Show evidence (2 references)

PMID:19631568 SUPPORT DIRECT PRIMARY RESULT Model Organism

Cross-sectional age groups support selection in mouse liver while leaving differential survival versus proliferation unresolved.

+ 1 more reference

Placental Labyrinth Dysmorphogenesis partially recapitulates fidelity: moderate observes: tissue Nsdhl mouse alleles exhibit a thin labyrinth, reduced fetal vessels, and reduced trophoblast proliferation.

Limitations: Placental findings and timing vary by allele. Rodent placental X-inactivation differs from humans, and human placental pathology has not been established.

Show evidence (2 references)

PMID:15639195 SUPPORT DIRECT PRIMARY RESULT Model Organism

Several mouse alleles show a placental structural phenotype associated with prenatal lethality; it does not establish the cause of every male loss or a human placental lesion.

+ 1 more reference

Reduced EGFR Signaling partially recapitulates fidelity: moderate observes: cellular NSDHL-null mouse skin has reduced activated EGFR and downstream signals with reduced proliferation.

Limitations: These are mouse skin observations. Similar signaling changes have not been demonstrated in human CHILD lesions, and they do not imply universal epidermal hyperproliferation.

Show evidence (2 references)

PMID:23125191 SUPPORT DIRECT PRIMARY RESULT Model Organism

"The reduced intracellular EGFR staining was accompanied by a marked loss of phosphorylated (activated) Y1173-EGFR ... signal in the NSDHL-null areas."

NSDHL-null patches of mouse skin had reduced activated EGFR; the original sentence also reports reduced ERK and AKT phosphorylation.

+ 1 more reference

Impaired Anagen Hair Growth partially recapitulates fidelity: moderate observes: tissue Mutant mouse skin has impaired anagen growth despite apparently normal early follicle morphology.

Limitations: The hair-cycle observations are murine; they do not establish a specific SHH defect in patient follicles.

Show evidence (1 reference)

PMID:19631568 SUPPORT DIRECT PRIMARY RESULT Model Organism

"The mutant follicles were smaller and shorter than adjacent WT follicles and lacked hair shafts, consistent with defective anagen hair growth."

Mouse mutant skin shows defective postnatal anagen growth; initial P2 follicle morphology was not grossly abnormal.

Show evidence (1 reference)

PMID:10710235 SUPPORT Human Clinical

"They provide animal models for the study of CHILD syndrome, a further human condition due to mutations in a gene of the cholesterol synthesis pathway."

The human gene-discovery paper explicitly nominates these mouse mutants as models for CHILD syndrome, which is the model-level claim.

Conditional Nsdhl ablation in radial glia

Exon-5 deletion driven by hGFAP-cre in radial-glial lineages begins during embryonic CNS development. Mutant males are live-born but develop ataxia and severe postnatal neurodegeneration; the reported animals died at P12-P20. The model establishes consequences of tissue-specific NSDHL loss, not the clinical phenotype of a particular human CK hypomorphic allele. Isolated granule-cell rescue experiments are recorded separately as cell-culture models.

Species

Mouse

Genotype

Nsdhl(tm1.1Hrm) conditional allele, GFAP-cre driver

Genes

NSDHL hgnc:13398

Publication

PMID:25652406

Pathograph links

Impaired Hedgehog Signal Transduction partially recapitulates fidelity: moderate observes: tissue Conditional mutant cerebella show reduced SHH target-gene and Gli1 reporter responses in vivo.

Limitations: Bulk tissue and reporter measurements are in a conditional-null mouse CNS, not human CHILD skin or limb tissue. They do not establish that every migration or survival defect is mediated through SHH.

Show evidence (1 reference)

PMID:25652406 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Using mice that express lacZ under the control of the Gli1 promoter, we were also able to demonstrate variable, but reduced, induction of this SHH response gene in vivo"

A separate reporter experiment demonstrates reduced SHH response in the conditional mouse CNS.

Show evidence (1 reference)

PMID:25652406 SUPPORT Model Organism

"Since hemizygous male mice with Nsdhl mutations die by midgestation, we generated a conditional targeted Nsdhl mutation (Nsdhl(tm1.1Hrm)) to investigate the essential role of cholesterol in the early postnatal CNS."

States why this conditional model exists and what it is a model of, which is the model-level claim.

Labrador Retriever NSDHL deletion

A female Labrador Retriever and her crossbred daughter carried a 14,399-base-pair deletion removing the final three NSDHL exons and had a patterned cornification disorder. Their lesions were bilateral and Blaschko-linear, without the typical human limb-reduction phenotype. Two male littermates died at birth but were not genotyped; those deaths cannot establish segregation of a lethal NSDHL genotype.

Species

Dog

Genotype

Heterozygous deletion removing the last three exons of NSDHL

Genes

NSDHL hgnc:13398

Publication

PMID:28739597

Pathograph links

X-Inactivation-Dependent NSDHL Expression Mosaicism partially recapitulates fidelity: moderate observes: tissue An NSDHL deletion in two affected females is associated with Blaschko-linear cutaneous disease, consistent with functional mosaicism.

Limitations: No allele-expression or enzyme assay directly established the mosaic mechanism, and no longitudinal clone depletion was measured. Bilateral lesions and lack of human-like limb reductions limit phenotype transfer. Male neonatal deaths were ungenotyped.

Readouts

Blaschko-linear cutaneous lesion distribution

Direction: ALTERED

Interpretation: Lesion distribution is compatible with functional X-inactivation mosaicism; it is not a direct allele-expression measurement.

Show evidence (1 reference)

PMID:28739597 SUPPORT Model Organism

"We investigated a female Labrador Retriever and her crossbred daughter, which both showed similar clinical lesions that followed Blaschko's lines."

Reports the lesion distribution behind this readout.

Show evidence (1 reference)

PMID:28739597 SUPPORT Model Organism

"Taken together, our genetic data and the known role of NSDHL in X-linked skin disorders strongly suggest that the identified structural variant in the NSDHL gene is causative for the phenotype in the two affected dogs."

Supports treating the canine phenotype as an NSDHL-driven model, with the authors' own hedged causal language preserved.

Show evidence (1 reference)

PMID:28739597 SUPPORT Model Organism

"Variants in the NSDHL gene cause CHILD syndrome in humans, and the bare patches (Bpa) and striated (Str) phenotypes in mice."

The authors situate their canine finding against the human disease and the established mouse models, which is what makes this dog a model for CHILD syndrome rather than an isolated veterinary case.

{ }

Source YAML

click to show

name: CHILD Syndrome
creation_date: "2026-08-13T19:20:00Z"
category: Mendelian
description: >-
  CHILD syndrome (congenital hemidysplasia with ichthyosiform nevus and limb defects) is an X-linked, usually male-lethal disorder caused by pathogenic NSDHL variants that impair post-squalene cholesterol biosynthesis. Heterozygous females have variable cutaneous and skeletal involvement, typically with unilateral ichthyosiform lesions and ipsilateral limb defects; bilateral or mild presentations and rare mosaic males are reported. Intellect is usually normal. NSDHL participates in sterol C4-demethylation, and experimental models distinguish effects of reduced cholesterol availability from effects of accumulated intermediates. Patient skin shows abnormal epidermal lipid secretion. X-inactivation creates mosaic expression, but the mechanism of the characteristic body-half distribution and any contribution of longitudinal clone depletion in human skin remain unresolved. Topical statins, alone or combined with cholesterol, have improved skin lesions in uncontrolled reports; these observations do not prove that cholesterol supplementation is required or that congenital skeletal defects are corrected. Hypomorphic NSDHL variants cause the distinct allelic disorder CK syndrome.
synonyms:
- CHILD syndrome
- congenital hemidysplasia with ichthyosiform nevus and limb defects
- congenital hemidysplasia with ichthyosiform erythroderma and limb defects
- CHILD nevus
disease_term:
  preferred_term: CHILD syndrome
  term:
    id: MONDO:0010621
    label: CHILD syndrome
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    notes: >-
      An X-linked Mendelian disorder whose clinical logic - mosaic expression
      under random X inactivation, male lethality - is genetic rather than
      organ-system based.
  - classification_value: DERMATOLOGY
    notes: >-
      Unilateral ichthyosiform skin lesions are a major presenting manifestation, and topical treatments address the cutaneous component of the disorder.
  - classification_value: ENDOCRINOLOGY_METABOLISM
    notes: >-
      Also an inborn error of metabolism: an enzymatic block in post-squalene
      cholesterol biosynthesis, confirmed by the sterol profile.
  icimd_category:
  - classification_value: sterol_metabolism
    notes: >-
      ICIMD (Ferreira et al. 2021, PMID:33340416): group "Disorders of sterol
      metabolism" under category "Disorders of lipid metabolism". NSDHL is the
      C4-demethylation-complex sterol dehydrogenase/decarboxylase of the distal
      cholesterol pathway.
  isds_skeletal_category:
  - classification_value: chondrodysplasia_punctata
    notes: >-
      ISDS Nosology of Genetic Skeletal Disorders, 2023 revision (Unger et al.,
      PMID:36779427), group 23 "Chondrodysplasia punctata (CDP) group", row
      NOS 23-0030 "Congenital hemidysplasia, ichthyosis, limb defects (CHILD)
      syndrome, NSDHL-related" (MIM 308050). The placement is the nosology's,
      not an inference from the skeletal phenotype: CHILD syndrome is grouped
      with the other CDPs because affected infants show punctate epiphyseal
      calcification, and it sits alongside the other post-squalene
      cholesterol-pathway member of the group, CDPX2 (EBP). Note the group is
      radiographically rather than mechanistically defined, so CHILD's nearest
      mechanistic relatives in dismech - Smith-Lemli-Opitz syndrome and the other
      sterol-biosynthesis disorders - are not group-23 entities.
parents:
- sterol biosynthesis disorder
- X-linked ichthyosis syndrome
references:
- reference: PMID:21290788
  title: "NSDHL-Related Disorders."
  tags:
  - GeneReviews
- reference: PMID:24060582
  title: "The role of abnormalities in the distal pathway of cholesterol synthesis in the Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects (CHILD) syndrome."
- reference: PMID:21753784
  title: "Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism."

- reference: PMID:10710235
  title: "Mutations in the NSDHL gene, encoding a 3beta-hydroxysteroid dehydrogenase, cause CHILD syndrome."
- reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
  title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
  tags:
  - GeneReviews
- reference: PMID:11907515
  title: "A novel missense mutation of NSDHL in an unusual case of CHILD syndrome showing bilateral, almost symmetric involvement."
- reference: PMID:21129721
  title: Hypomorphic temperature-sensitive alleles of NSDHL cause CK syndrome.
- reference: PMID:15639195
  title: Placental defects are associated with male lethality in bare patches and striated embryos deficient in the NAD(P)H Steroid Dehydrogenase-like (NSDHL) Enzyme.
- reference: PMID:23125191
  title: Targeting C4-demethylating genes in the cholesterol pathway sensitizes cancer cells to EGF receptor inhibitors via increased EGF receptor degradation.
- reference: PMID:19631568
  title: Developmental expression pattern of the cholesterogenic enzyme NSDHL and negative selection of NSDHL-deficient cells in the heterozygous Bpa(1H)/+ mouse.
- reference: PMID:40222685
  title: "Comprehensive survey of disease-causing missense mutations of the cholesterol synthesis enzyme NSDHL: Low temperature and a chemical chaperone rescue low protein expression of select mutants."
- reference: PMID:25652406
  title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
- reference: PMID:16776722
  title: "Abnormal lamellar granules in a case of CHILD syndrome."
- reference: PMID:17028112
  title: Analysis of Nsdhl-deficient embryos reveals a role for Hedgehog signaling in early placental development.
- reference: PMID:7408908
  title: "The CHILD syndrome. Congenital hemidysplasia with ichthyosiform erythroderma and limb defects."
- reference: PMID:34957706
  title: A novel NSDHL variant in CHILD syndrome with gastrointestinal manifestations and localized skin involvement.
- reference: PMID:7640190
  title: "Epidermal nevus syndromes."
- reference: PMID:10369263
  title: "The gene mutated in bare patches and striated mice encodes a novel 3beta-hydroxysteroid dehydrogenase."
- reference: PMID:29341259
  title: "CHILD syndrome mimicking verrucous nevus in a Chinese patient responded well to the topical therapy of compound of simvastatin and cholesterol."
- reference: PMID:41625319
  title: "Diagnostic Utility of Optical Genome Mapping in X-Linked Dominant Genodermatoses: Incontinentia Pigmenti and CHILD Syndrome."
- reference: PMID:33139364
  title: "Novel NSDHL gene variant for congenital hemidysplasia with ichthyosiform erythroderma and limb defects (CHILD) syndrome."
- reference: PMID:25845514
  title: "CHILD Syndrome: Successful Treatment of Skin Lesions with Topical Simvastatin/Cholesterol Ointment--A Case Report."
- reference: PMID:31365666
  title: "CHILD syndrome: successful treatment of skin lesions with topical lovastatin and cholesterol lotion."
- reference: PMID:29687057
  title: 'Pathogenesis-based therapy: Cutaneous abnormalities of CHILD syndrome successfully treated with topical simvastatin monotherapy.'
- reference: PMID:39431262
  title: '5% Simvastatin Ointment as Treatment for Congenital Hemidysplasia with Ichthyosiform Erythroderma and Limb Defects (CHILD) Syndrome in a 4-year-old Female: A Case Report.'
- reference: PMID:39565229
  title: Improvement of Skin Lesions in an Adult with CHILD Syndrome Treated with 2% Ketoconazole Cream.
- reference: PMID:28739597
  title: "A Large Deletion in the NSDHL Gene in Labrador Retrievers with a Congenital Cornification Disorder."
- reference: PMID:10710233
  title: "CHILD syndrome caused by deficiency of 3beta-hydroxysteroid-delta8, delta7-isomerase."
- reference: PMID:39953436
  title: "Unilateral widespread inflammatory linear verrucous epidermal nevus with ipsilateral limb contracture along the lines of Blaschko: A case report."
- reference: PMID:36504312
  title: 'Etiological identification of recurrent male fatality due to a novel NSDHL gene mutation using trio whole-exome sequencing: A rare case report and literature review.'
- reference: PMID:32886633
  title: Topical Cholesterol/Simvastatin Gel for the Treatment of CHILD Syndrome in an Adolescent.
inheritance:
- name: X-linked dominant inheritance with male lethality
  inheritance_term:
    preferred_term: X-linked dominant inheritance
    term:
      id: HP:0001423
      label: X-linked dominant inheritance
  description: >-
    CHILD syndrome is inherited in an X-linked manner and predominantly affects heterozygous females because hemizygous males with severe loss-of-function variants usually do not survive gestation. Rare surviving males with postzygotic mosaicism have been reported. A heterozygous mother has a 50% chance of transmitting the pathogenic variant in each pregnancy; the expected live-born distribution is altered by male lethality. Molecular recurrence-risk assessment requires a pathogenic or likely pathogenic variant, not a variant of uncertain significance.
  evidence:
  - reference: PMID:10710235
    reference_title: "Mutations in the NSDHL gene, encoding a 3beta-hydroxysteroid dehydrogenase, cause CHILD syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We report for the first time that CHILD syndrome (MIM 308050), an X-linked
      dominant, male-lethal trait characterized by an inflammatory nevus with
      striking lateralization and strict midline demarcation, as well as
      ipsilateral hypoplasia of the body is caused by mutations in the gene NSDHL
      located at Xq28
    explanation: >-
      The gene-discovery paper states the X-linked dominant, male-lethal mode of
      inheritance alongside the causal locus.
  - reference: PMID:21290788
    reference_title: "NSDHL-Related Disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      CHILD syndrome is usually male lethal during gestation and thus
      predominantly affects females.
    explanation: >-
      GeneReviews states the male-lethal consequence and the resulting female
      predominance.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:21290788
    reference_title: "NSDHL-Related Disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      However, since studies suggest that male conceptuses with an NSDHL
      pathogenic variant generally abort or resorb spontaneously, the expected
      live-born distribution is: 33% heterozygous (typically) affected females;
      33% unaffected females; and 33% unaffected males.
    explanation: >-
      Supplies the quantitative recurrence-risk figures that this description
      would otherwise only paraphrase, including the reason the live-born ratios
      depart from the usual X-linked expectation.
    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: If the mother of a proband has an NSDHL pathogenic variant, the chance of transmitting it in each pregnancy is 50%.
    explanation: GeneReviews gives the transmission probability per pregnancy; this differs from the distribution among live births.
- name: Functional mosaicism from random X inactivation
  description: >-
    Heterozygous females are functional mosaics because of X-inactivation; this is distinct from a postzygotic DNA variant. In cultures from one studied patient, both NSDHL alleles were present in genomic DNA from affected and unaffected skin. Affected keratinocytes expressed the mutant allele, whereas unaffected keratinocytes expressed the wild-type allele. Affected fibroblasts retained expression of both alleles. This tissue-specific expression pattern does not establish the developmental origin of the body-half boundary or longitudinal clearance of mutant cells in human skin.
  evidence:
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: 'However, RT-PCR on cDNA from keratinocytes and fibroblasts isolated from the affected versus clinically unaffected side in Patient #1 demonstrated exclusive expression of the mutant allele by affected cultured keratinocytes, while unaffected keratinocytes solely expressed the wild type allele'
    explanation: Cultures from one patient showed side-specific NSDHL allele expression; this is not a longitudinal measure of cell clearance.
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Only the normal allele was expressed by unaffected fibroblasts, but fibroblasts from the clinically affected area expressed an approximately even distribution of normal and mutant alleles.
    explanation: Fibroblast expression in affected skin did not match the exclusively mutant keratinocyte pattern.
  - reference: PMID:11907515
    reference_title: "A novel missense mutation of NSDHL in an unusual case of CHILD syndrome showing bilateral, almost symmetric involvement."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Apparently, the effect of random X-inactivation is responsible for
      different patterns of cutaneous involvement in female carriers of NSDHL
      mutations.
    explanation: >-
      Attributes the variable cutaneous distribution, including the exceptional
      bilateral case, to the X-inactivation pattern rather than to allele
      identity.

genetic:
- name: NSDHL
  gene_term:
    preferred_term: NSDHL
    term:
      id: hgnc:13398
      label: NSDHL
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  notes: >-
    NSDHL loss-of-function variants cause CHILD syndrome. The Xq28 gene encodes the dehydrogenase/decarboxylase component of sterol C4-demethylation. Reported alleles include missense, premature termination, frameshift and exon-deletion variants. Familial transmission can occur with marked variability, including a mother with mild skin changes. Rare male survival can reflect postzygotic mosaicism. Hypomorphic variants retaining partial function cause the distinct allelic CK syndrome.
  evidence:
  - reference: PMID:10710235
    reference_title: "Mutations in the NSDHL gene, encoding a 3beta-hydroxysteroid dehydrogenase, cause CHILD syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      SSCA and genomic sequence analysis of NSDHL identified in 6 patients with
      CHILD syndrome, including one boy as well as a mother and her daughter,
      mutations potentially impairing protein function.
    explanation: >-
      Establishes NSDHL variants as the molecular cause in a patient series.
  - reference: PMID:21290788
    reference_title: "NSDHL-Related Disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The diagnosis of CHILD syndrome is established in a female proband with a
      heterozygous NSDHL pathogenic variant identified by molecular genetic
      testing that results in loss of functional decarboxylating
      sterol-4-alpha-carboxylate 3-dehydrogenase, the protein encoded by NSDHL.
    explanation: >-
      GeneReviews states the diagnostic criterion and the loss-of-function
      consequence at the protein level.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:21129721
    reference_title: Hypomorphic temperature-sensitive alleles of NSDHL cause CK syndrome.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: These two mutations, which alter protein folding, show temperature-sensitive protein stability and complementation in Erg26-deficient yeast.
    explanation: The original CK syndrome study demonstrates residual, temperature-sensitive function of its two studied alleles, supporting the distinction from severe CHILD loss of function.
  - reference: PMID:34957706
    reference_title: A novel NSDHL variant in CHILD syndrome with gastrointestinal manifestations and localized skin involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: The variant was confirmed by targeted Sanger sequencing for DNA from both skin tissues and blood. Testing of parental DNA indicated maternal inheritance, with her father testing negative for the variant.
    explanation: The adult gastrointestinal case confirms maternal transmission of the reported NSDHL frameshift.
pathophysiology:
- name: NSDHL Loss of Function
  biological_scale: MOLECULAR
  description: >-
    Pathogenic NSDHL variants impair the sterol dehydrogenase/decarboxylase component of the C4-demethylation complex. An expression study of thirteen disease-associated missense variants and one deletion found reduced protein abundance; temperature or glycerol partially increased abundance for some variants. These assays do not establish that all variants act through the same folding defect or that rescued protein has restored catalytic activity.
  molecular_functions:
  - preferred_term: sterol-4-alpha-carboxylate 3-dehydrogenase (NSDHL) activity
    modifier: LOSS_OF_FUNCTION
    term:
      id: GO:0000252
      label: 3-beta-hydroxysteroid dehydrogenase [NAD(P)+]/C4-decarboxylase activity
  genes:
  - preferred_term: NSDHL
    term:
      id: hgnc:13398
      label: NSDHL
  downstream:
  - target: Impaired Sterol C4-Demethylation
    description: Loss of the NSDHL enzyme component impairs this biosynthetic step.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:15639195
      reference_title: Placental defects are associated with male lethality in bare patches and striated embryos deficient in the NAD(P)H Steroid Dehydrogenase-like (NSDHL) Enzyme.
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: BACKGROUND
      directness: DIRECT
      snippet: NSDHL is a 3beta-hydroxysterol dehydrogenase that is involved in the removal of C-4 methyl groups in one of the later steps of cholesterol biosynthesis.
      explanation: The primary mouse paper describes the established enzymatic function in its background.
  - target: Increased Receptor Lysosomal Trafficking
    description: Experimental NSDHL depletion alters receptor handling; the molecular intermediates and relevance to human skin remain incompletely defined.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:23125191
      reference_title: Targeting C4-demethylating genes in the cholesterol pathway sensitizes cancer cells to EGF receptor inhibitors via increased EGF receptor degradation.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: In contrast, depletion of either SC4MOL or NSDHL significantly reduced the amount of fluorescently labeled EGFR ... associated with RAB11-positive recycling endosomes after 30 minutes of EGF stimulation.
      explanation: NSDHL knockdown in experimental cells reduced receptor localization to recycling endosomes; this is not a patient-tissue result.
  - target: Impaired Anagen Hair Growth
    description: Nsdhl-deficient mouse skin shows defective anagen progression, with the intervening signaling sequence unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:19631568
      reference_title: Developmental expression pattern of the cholesterogenic enzyme NSDHL and negative selection of NSDHL-deficient cells in the heterozygous Bpa(1H)/+ mouse.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: The mutant follicles were smaller and shorter than adjacent WT follicles and lacked hair shafts, consistent with defective anagen hair growth.
      explanation: Mouse mutant skin shows defective postnatal anagen growth; initial P2 follicle morphology was not grossly abnormal.
  - target: Ipsilateral body hypoplasia
    description: NSDHL dysfunction causes the developmental syndrome that includes ipsilateral body hypoplasia. The intervening tissue-specific processes are unresolved; this edge does not assign the phenotype to a demonstrated Hedgehog or clone-clearance pathway.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:10710235
      reference_title: Mutations in the NSDHL gene, encoding a 3beta-hydroxysteroid dehydrogenase, cause CHILD syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      directness: INDIRECT
      snippet: We report for the first time that CHILD syndrome ... an X-linked dominant, male-lethal trait characterized by an inflammatory nevus with striking lateralization and strict midline demarcation, as well as ipsilateral hypoplasia of the body is caused by mutations in the gene NSDHL located at Xq28
      explanation: The primary genetic report identifies NSDHL as the cause of the syndrome with ipsilateral body hypoplasia. It does not resolve the intervening developmental pathway.
  - target: Ipsilateral limb hypoplasia or aplasia
    description: NSDHL dysfunction underlies the limb-reduction phenotype through incompletely resolved developmental processes. A specific Hedgehog-mediated route in human limbs is not established by the mouse neural-culture experiments.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:10710235
      reference_title: Mutations in the NSDHL gene, encoding a 3beta-hydroxysteroid dehydrogenase, cause CHILD syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      directness: INDIRECT
      snippet: We report for the first time that CHILD syndrome ... an X-linked dominant, male-lethal trait characterized by an inflammatory nevus with striking lateralization and strict midline demarcation, as well as ipsilateral hypoplasia of the body is caused by mutations in the gene NSDHL located at Xq28
      explanation: The primary genetic report identifies NSDHL as the cause of the syndrome with ipsilateral body hypoplasia. It does not resolve the intervening developmental pathway.
    - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
      reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: INDIRECT
      snippet: CHILD syndrome is characterized by unilateral distribution of ichthyosiform skin lesions and ipsilateral limb defects that range from shortening of the metacarpals and phalanges to absence of the entire limb.
      explanation: GeneReviews identifies ipsilateral limb reduction as a defining manifestation of the NSDHL disorder.
  evidence:
  - reference: PMID:40222685
    reference_title: "Comprehensive survey of disease-causing missense mutations of the cholesterol synthesis enzyme NSDHL: Low temperature and a chemical chaperone rescue low protein expression of select mutants."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Here we show that protein expression levels were low for all mutants, but
      some could be rescued by a lower temperature (30°C vs. 37°C) and/or the
      chemical chaperone glycerol.
    explanation: >-
      The expression assay reports lower steady-state abundance and partial abundance rescue; enzymatic rescue is not established by this quote.
  - reference: PMID:10710235
    reference_title: "Mutations in the NSDHL gene, encoding a 3beta-hydroxysteroid dehydrogenase, cause CHILD syndrome."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      (NAD(P)H steroid dehydrogenase-like protein) encoding a 3beta-hydroxysteroid
      dehydrogenase functioning in the cholesterol biosynthetic pathway
    explanation: >-
      Identifies the enzymatic function that is lost.

    quote_role: BACKGROUND
  mechanism_confidence: ESTABLISHED
- name: Impaired Sterol C4-Demethylation
  description: Impaired NSDHL activity limits removal of C4 methyl groups from sterol intermediates. Reduced downstream cholesterol supply and upstream precursor accumulation are distinct biochemical consequences.
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:15639195
    reference_title: Placental defects are associated with male lethality in bare patches and striated embryos deficient in the NAD(P)H Steroid Dehydrogenase-like (NSDHL) Enzyme.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: NSDHL is a 3beta-hydroxysterol dehydrogenase that is involved in the removal of C-4 methyl groups in one of the later steps of cholesterol biosynthesis.
    explanation: The primary mouse paper describes the established enzymatic function in its background.
  - reference: PMID:24060582
    reference_title: The role of abnormalities in the distal pathway of cholesterol synthesis in the Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects (CHILD) syndrome.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CHILD syndrome results from loss of function mutations in the NSDHL gene, which leads to inhibition of cholesterol synthesis and accumulation of toxic metabolic intermediates in affected tissues.
    explanation: The review describes reduced synthesis and precursor accumulation; these are separate consequences of the biosynthetic block.
  biological_processes:
  - preferred_term: cholesterol biosynthetic process
    term:
      id: GO:0006695
      label: cholesterol biosynthetic process
    modifier: DECREASED
  downstream:
  - target: Reduced Cholesterol Availability
    description: The biosynthetic defect can reduce cholesterol availability within affected cells.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:24060582
      reference_title: The role of abnormalities in the distal pathway of cholesterol synthesis in the Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects (CHILD) syndrome.
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: DIRECT
      snippet: CHILD syndrome results from loss of function mutations in the NSDHL gene, which leads to inhibition of cholesterol synthesis and accumulation of toxic metabolic intermediates in affected tissues.
      explanation: The review describes reduced synthesis and precursor accumulation; these are separate consequences of the biosynthetic block.
  - target: C4-Methylsterol Accumulation
    description: Intermediates upstream of the enzymatic block accumulate.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:25652406
      reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: The concentration of methylsterols was significantly higher in NsdhlΔ5/Y GCPs than Nsdhlflx5/Y GCPs (P < 0.002) in all four culture conditions.
      explanation: Cultured conditional-null mouse granule-cell precursors accumulate methylsterols under the tested conditions.
- name: Reduced Cholesterol Availability
  description: Cholesterol supply can be insufficient within affected cells despite near-normal circulating sterols. In conditional-null mouse granule-cell cultures, cholesterol or LDL supplementation restored much of the impaired SHH response. This does not imply uniform systemic hypocholesterolemia.
  biological_scale: MOLECULAR
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:24060582
    reference_title: The role of abnormalities in the distal pathway of cholesterol synthesis in the Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects (CHILD) syndrome.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CHILD syndrome results from loss of function mutations in the NSDHL gene, which leads to inhibition of cholesterol synthesis and accumulation of toxic metabolic intermediates in affected tissues.
    explanation: The review describes reduced synthesis and precursor accumulation; these are separate consequences of the biosynthetic block.
  - reference: PMID:25652406
    reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Taken together, these results demonstrate that cholesterol depletion is sufficient to account for virtually all of the reduced response of mutant GCPs to SHH in vitro.
    explanation: Cholesterol supplementation experiments locate a major SHH-response defect in the recipient granule-cell cultures.
  chemical_entities:
  - preferred_term: cholesterol
    term:
      id: CHEBI:16113
      label: cholesterol
    modifier: DECREASED
  downstream:
  - target: Impaired Hedgehog Signal Transduction
    description: Cultured granule-cell experiments support impaired reception of SHH when cholesterol is limiting.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:25652406
      reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Taken together, these results demonstrate that cholesterol depletion is sufficient to account for virtually all of the reduced response of mutant GCPs to SHH in vitro.
      explanation: Cholesterol supplementation experiments locate a major SHH-response defect in the recipient granule-cell cultures.
  - target: Impaired Epidermal Lamellar Body Secretion
    description: Reduced availability of a barrier lipid is proposed to contribute to the abnormal secretory apparatus; patient ultrastructure and treatment response do not isolate this contribution from precursor effects.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:24060582
      reference_title: The role of abnormalities in the distal pathway of cholesterol synthesis in the Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects (CHILD) syndrome.
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: DIRECT
      snippet: CHILD syndrome results from loss of function mutations in the NSDHL gene, which leads to inhibition of cholesterol synthesis and accumulation of toxic metabolic intermediates in affected tissues.
      explanation: The review describes reduced synthesis and precursor accumulation; these are separate consequences of the biosynthetic block.
    - reference: PMID:21753784
      reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Individual organelles displayed few internal lamellae, which often fused prematurely into intracellular, multivesicular bodies that were incompletely secreted
      explanation: Pretreatment patient biopsies demonstrate abnormal lamellar-body architecture and incomplete secretion.
- name: C4-Methylsterol Accumulation
  description: C4-methylsterol intermediates accumulate upstream of the NSDHL block. Mouse granule-cell experiments associate precursor reduction with improved viability, but different sterol species and endpoints need separate interpretation. The same intervention did not restore SHH-induced Gli1 expression.
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:25652406
    reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: The concentration of methylsterols was significantly higher in NsdhlΔ5/Y GCPs than Nsdhlflx5/Y GCPs (P < 0.002) in all four culture conditions.
    explanation: Cultured conditional-null mouse granule-cell precursors accumulate methylsterols under the tested conditions.
  - reference: PMID:25652406
    reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Ketoconazole treatment did not affect the viability of WT cells, but it significantly increased mutant cell viability (from 65 to 78%; Fig. 7B).
    explanation: An upstream synthesis inhibitor improved viability in mutant cultures; this supports a precursor-associated injury component but does not identify every accumulated sterol as toxic.
  - reference: PMID:25652406
    reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Although the reduction of methylsterol levels by ketoconazole treatment apparently improved the viability and cell morphology of the mutant GCPs, it had no effect on Gli1 expression
    explanation: Cell viability and SHH transcriptional responses were experimentally dissociable; lowering precursors alone did not restore this readout.
  downstream:
  - target: Impaired Epidermal Lamellar Body Secretion
    description: Precursor-associated toxicity is a proposed contributor to the secretory abnormality in patient skin; the specific responsible sterols and intermediate steps remain unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:24060582
      reference_title: The role of abnormalities in the distal pathway of cholesterol synthesis in the Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects (CHILD) syndrome.
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: DIRECT
      snippet: CHILD syndrome results from loss of function mutations in the NSDHL gene, which leads to inhibition of cholesterol synthesis and accumulation of toxic metabolic intermediates in affected tissues.
      explanation: The review describes reduced synthesis and precursor accumulation; these are separate consequences of the biosynthetic block.
    - reference: PMID:21753784
      reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Individual organelles displayed few internal lamellae, which often fused prematurely into intracellular, multivesicular bodies that were incompletely secreted
      explanation: Pretreatment patient biopsies demonstrate abnormal lamellar-body architecture and incomplete secretion.
- name: X-Inactivation-Dependent NSDHL Expression Mosaicism
  description: X-inactivation creates functional mosaicism in heterozygous females. In one patient, cultured keratinocytes from affected and unaffected skin expressed different NSDHL alleles, while affected fibroblasts retained both. These observations do not explain the precise midline boundary or demonstrate longitudinal cell clearance.
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: 'However, RT-PCR on cDNA from keratinocytes and fibroblasts isolated from the affected versus clinically unaffected side in Patient #1 demonstrated exclusive expression of the mutant allele by affected cultured keratinocytes, while unaffected keratinocytes solely expressed the wild type allele'
    explanation: Cultures from one patient showed side-specific NSDHL allele expression; this is not a longitudinal measure of cell clearance.
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Only the normal allele was expressed by unaffected fibroblasts, but fibroblasts from the clinically affected area expressed an approximately even distribution of normal and mutant alleles.
    explanation: Fibroblast expression in affected skin did not match the exclusively mutant keratinocyte pattern.
  cell_types:
  - preferred_term: keratinocyte
    term:
      id: CL:0000312
      label: keratinocyte
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  biological_processes:
  - preferred_term: random inactivation of X chromosome
    term:
      id: GO:0060816
      label: random inactivation of X chromosome
  downstream:
  - target: Age-Dependent Depletion of NSDHL-Deficient Cells
    description: Age-dependent changes in mutant-cell representation occur in mosaic mouse tissues, with differential proliferation and survival unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:19631568
      reference_title: Developmental expression pattern of the cholesterogenic enzyme NSDHL and negative selection of NSDHL-deficient cells in the heterozygous Bpa(1H)/+ mouse.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: These data suggest that the higher percentage of WT hepatocytes present in livers from older Bpa1H females is the cumulative result of postnatal differences in either the growth rate or survival of WT vs mutant hepatocytes.
      explanation: Cross-sectional age groups support selection in mouse liver while leaving differential survival versus proliferation unresolved.
  - target: Impaired Epidermal Lamellar Body Secretion
    description: The patient expression and biopsy findings associate mutant-expressing epidermis with the secretory lesion; the lineage and selection mechanisms producing the distribution remain unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:21753784
      reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: 'However, RT-PCR on cDNA from keratinocytes and fibroblasts isolated from the affected versus clinically unaffected side in Patient #1 demonstrated exclusive expression of the mutant allele by affected cultured keratinocytes, while unaffected keratinocytes solely expressed the wild type allele'
      explanation: Cultures from one patient showed side-specific NSDHL allele expression; this is not a longitudinal measure of cell clearance.
    - reference: PMID:21753784
      reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Individual organelles displayed few internal lamellae, which often fused prematurely into intracellular, multivesicular bodies that were incompletely secreted
      explanation: Pretreatment patient biopsies demonstrate abnormal lamellar-body architecture and incomplete secretion.
  - target: Strict midline demarcation of skin lesions
    description: Functional mosaicism contributes to the distribution of affected skin. The developmental steps producing a sharp body-midline boundary remain unknown, and bilateral patterns can occur.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:11907515
      reference_title: A novel missense mutation of NSDHL in an unusual case of CHILD syndrome showing bilateral, almost symmetric involvement.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      directness: INDIRECT
      snippet: Apparently, the effect of random X-inactivation is responsible for different patterns of cutaneous involvement in female carriers of NSDHL mutations.
      explanation: The authors attribute variable cutaneous distribution to X-inactivation. This supports an indirect contribution to the usual lateralized pattern, not a demonstrated mechanism for the precise boundary geometry.
- name: Age-Dependent Depletion of NSDHL-Deficient Cells
  description: 'Mouse liver and brain show an age-dependent reduction in the representation of NSDHL-deficient cells. This is tissue-specific: NSDHL-negative skin persisted at eight weeks. The mechanism may involve differential survival or proliferation, and the result has not been measured longitudinally in human CHILD skin.'
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:19631568
    reference_title: Developmental expression pattern of the cholesterogenic enzyme NSDHL and negative selection of NSDHL-deficient cells in the heterozygous Bpa(1H)/+ mouse.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: These data suggest that the higher percentage of WT hepatocytes present in livers from older Bpa1H females is the cumulative result of postnatal differences in either the growth rate or survival of WT vs mutant hepatocytes.
    explanation: Cross-sectional age groups support selection in mouse liver while leaving differential survival versus proliferation unresolved.
  - reference: PMID:19631568
    reference_title: Developmental expression pattern of the cholesterogenic enzyme NSDHL and negative selection of NSDHL-deficient cells in the heterozygous Bpa(1H)/+ mouse.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: 'The average percentage of NSDHL positive hepatocytes in livers from six Bpa1H P6 females was 52 (SD: 5). Among six mutant livers at P25, the average percentage of NSDHL positive hepatocytes increased to 62 (SD: 9).'
    explanation: The comparison concerns different mouse age groups and liver tissue, not serial biopsies of human skin.
- name: Impaired Epidermal Lamellar Body Secretion
  description: Patient biopsies show lamellar bodies with few internal lamellae, premature fusion, and incomplete secretion. The resulting retention of organelle material is a cellular secretory defect distinct from the extracellular lipid architecture it produces.
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Individual organelles displayed few internal lamellae, which often fused prematurely into intracellular, multivesicular bodies that were incompletely secreted
    explanation: Pretreatment patient biopsies demonstrate abnormal lamellar-body architecture and incomplete secretion.
  - reference: PMID:16776722
    reference_title: "Abnormal lamellar granules in a case of CHILD syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Electron microscopy revealed vesicular structures in the intercellular
      spaces of the stratum corneum and vacuoles or vesicular structures in
      upper prickle cell layer. Some of them can be recognized as abnormal
      lamellar granules. Within the foamy cells in the papillary dermis, large
      vacuoles were found.
    explanation: >-
      Independent ultrastructural confirmation of the abnormal lamellar granules
      and of the dermal foam cells this description asserts, from a different
      patient and laboratory than the treatment study.

  cell_types:
  - preferred_term: keratinocyte
    term:
      id: CL:0000312
      label: keratinocyte
  downstream:
  - target: Disorganized Stratum Corneum Lipid Lamellae
    description: Incomplete secretion leaves sparse and disorganized extracellular lamellar material.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:21753784
      reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Finally, and as a result of impaired secretion, the stratum corneum extracellular matrix displayed a paucity of secreted lamellar material, interspersed with abundant non-lamellar vesicles
      explanation: The patient ultrastructure links impaired secretion to disorganized extracellular lipid lamellae.
- name: Disorganized Stratum Corneum Lipid Lamellae
  description: The stratum corneum extracellular matrix in affected skin contains sparse lamellar material mixed with non-lamellar vesicles, consistent with a defective lipid barrier. Clinically unaffected skin can retain mild ultrastructural abnormalities.
  biological_scale: TISSUE
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Finally, and as a result of impaired secretion, the stratum corneum extracellular matrix displayed a paucity of secreted lamellar material, interspersed with abundant non-lamellar vesicles
    explanation: The patient ultrastructure links impaired secretion to disorganized extracellular lipid lamellae.
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Although no visible ichthyosiform features could be appreciated either clinically or by light microscopy, ultrastructural images displayed mild abnormalities in lamellar body internal contents and lamellar bilayer organization
    explanation: Clinically unaffected skin from one patient had subtle structural abnormalities, so visible normality is not proof of a fully normal lipid barrier.
  biological_processes:
  - preferred_term: establishment of skin barrier
    term:
      id: GO:0061436
      label: establishment of skin barrier
    modifier: DECREASED
  downstream:
  - target: Ichthyosiform nevus
    description: The barrier-lipid abnormality contributes to scaling and inflammation. The relative roles of cholesterol deficiency and individual precursors remain incompletely resolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:21753784
      reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Individual organelles displayed few internal lamellae, which often fused prematurely into intracellular, multivesicular bodies that were incompletely secreted
      explanation: Pretreatment patient biopsies demonstrate abnormal lamellar-body architecture and incomplete secretion.
    - reference: PMID:24060582
      reference_title: The role of abnormalities in the distal pathway of cholesterol synthesis in the Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects (CHILD) syndrome.
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: DIRECT
      snippet: CHILD syndrome results from loss of function mutations in the NSDHL gene, which leads to inhibition of cholesterol synthesis and accumulation of toxic metabolic intermediates in affected tissues.
      explanation: The review describes reduced synthesis and precursor accumulation; these are separate consequences of the biosynthetic block.
- name: Impaired Hedgehog Signal Transduction
  description: Conditional Nsdhl-null mouse granule-cell cultures have an impaired response to SHH that is strongly improved by cholesterol supply. Reduced reporter activity is also observed in mouse cerebellum and placenta. These findings concern signal reception and response; defective ligand processing and the precise mechanisms of human limb defects are not established.
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:25652406
    reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: We replicated the granule cell precursor proliferation defect in vitro and demonstrate that it results from defective signaling by SHH.
    explanation: The experiment is in cultured mouse granule-cell precursors rather than whole animals or human limb tissue.
  - reference: PMID:25652406
    reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Using mice that express lacZ under the control of the Gli1 promoter, we were also able to demonstrate variable, but reduced, induction of this SHH response gene in vivo
    explanation: A separate reporter experiment demonstrates reduced SHH response in the conditional mouse CNS.
  - reference: PMID:17028112
    reference_title: Analysis of Nsdhl-deficient embryos reveals a role for Hedgehog signaling in early placental development.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Further, affected placentas from mutant Nsdhl(Bpa-8H) male embryos demonstrate markedly decreased or no Ptch1-lacZ staining and no migration of Ihh expressing cells into the developing placenta.
    explanation: Placental reporter and cellular-distribution observations implicate Hedgehog signaling in this mouse allele.
  - reference: PMID:25652406
    reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Although the reduction of methylsterol levels by ketoconazole treatment apparently improved the viability and cell morphology of the mutant GCPs, it had no effect on Gli1 expression
    explanation: Cell viability and SHH transcriptional responses were experimentally dissociable; lowering precursors alone did not restore this readout.
  biological_processes:
  - preferred_term: smoothened signaling pathway
    term:
      id: GO:0007224
      label: smoothened signaling pathway
    modifier: DECREASED
  downstream:
  - target: Placental Labyrinth Dysmorphogenesis
    description: The mouse placental reporter and migration findings implicate Hedgehog signaling in the structural defect, without a definitive rescue establishing the full causal sequence.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:17028112
      reference_title: Analysis of Nsdhl-deficient embryos reveals a role for Hedgehog signaling in early placental development.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Further, affected placentas from mutant Nsdhl(Bpa-8H) male embryos demonstrate markedly decreased or no Ptch1-lacZ staining and no migration of Ihh expressing cells into the developing placenta.
      explanation: Placental reporter and cellular-distribution observations implicate Hedgehog signaling in this mouse allele.
    - reference: PMID:15639195
      reference_title: Placental defects are associated with male lethality in bare patches and striated embryos deficient in the NAD(P)H Steroid Dehydrogenase-like (NSDHL) Enzyme.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Although no consistent anomalies were identified in affected male embryos themselves, the labyrinth layer of the fetal placenta was always thinner, with fewer fetal vessels and decreased proliferation of labyrinth trophoblast cells.
      explanation: Several mouse alleles show a placental structural phenotype associated with prenatal lethality; it does not establish the cause of every male loss or a human placental lesion.
  notes: The upstream defect is in sterol metabolism; no primary ciliary assembly defect is established. Human limb and hair mechanisms cannot be inferred directly from CNS culture rescue.
- name: Placental Labyrinth Dysmorphogenesis
  description: Several Nsdhl mouse alleles show a thin placental labyrinth with reduced fetal vascularization and trophoblast proliferation. Embryonic death occurs at allele-dependent stages, including earlier death with Bpa1H. Placental abnormalities are associated with lethality in these models; the corresponding human mechanism remains unverified.
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:15639195
    reference_title: Placental defects are associated with male lethality in bare patches and striated embryos deficient in the NAD(P)H Steroid Dehydrogenase-like (NSDHL) Enzyme.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Although no consistent anomalies were identified in affected male embryos themselves, the labyrinth layer of the fetal placenta was always thinner, with fewer fetal vessels and decreased proliferation of labyrinth trophoblast cells.
    explanation: Several mouse alleles show a placental structural phenotype associated with prenatal lethality; it does not establish the cause of every male loss or a human placental lesion.
  - reference: PMID:17028112
    reference_title: Analysis of Nsdhl-deficient embryos reveals a role for Hedgehog signaling in early placental development.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Further, affected placentas from mutant Nsdhl(Bpa-8H) male embryos demonstrate markedly decreased or no Ptch1-lacZ staining and no migration of Ihh expressing cells into the developing placenta.
    explanation: Placental reporter and cellular-distribution observations implicate Hedgehog signaling in this mouse allele.
  cell_types:
  - preferred_term: trophoblast cell
    term:
      id: CL:0000351
      label: trophoblast cell
  biological_processes:
  - preferred_term: placenta development
    term:
      id: GO:0001890
      label: placenta development
    modifier: ABNORMAL
- name: Increased Receptor Lysosomal Trafficking
  description: NSDHL depletion in experimental cell systems reduces EGFR recycling and shifts receptor-associated signals toward late endosomal and lysosomal compartments. The assays use knockdown and model cells, not direct measurements in human CHILD lesions.
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:23125191
    reference_title: Targeting C4-demethylating genes in the cholesterol pathway sensitizes cancer cells to EGF receptor inhibitors via increased EGF receptor degradation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: In contrast, depletion of either SC4MOL or NSDHL significantly reduced the amount of fluorescently labeled EGFR ... associated with RAB11-positive recycling endosomes after 30 minutes of EGF stimulation.
    explanation: NSDHL knockdown in experimental cells reduced receptor localization to recycling endosomes; this is not a patient-tissue result.
  - reference: PMID:23125191
    reference_title: Targeting C4-demethylating genes in the cholesterol pathway sensitizes cancer cells to EGF receptor inhibitors via increased EGF receptor degradation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Conversely, SC4MOL and NSDHL-deficient cells showed an accelerated concentration of internalized fluorescently labeled EGF in RAB7-positive ... or EGFR in LAMP1-positive late endosomes
    explanation: Experimental depletion shifts receptor-associated signals toward late endosomal compartments.
  downstream:
  - target: Reduced EGFR Signaling
    description: Accelerated receptor degradation can reduce the signaling receptor pool; mouse-skin observations support reduced pathway activation in NSDHL-null regions.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:23125191
      reference_title: Targeting C4-demethylating genes in the cholesterol pathway sensitizes cancer cells to EGF receptor inhibitors via increased EGF receptor degradation.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: In contrast, depletion of either SC4MOL or NSDHL significantly reduced the amount of fluorescently labeled EGFR ... associated with RAB11-positive recycling endosomes after 30 minutes of EGF stimulation.
      explanation: NSDHL knockdown in experimental cells reduced receptor localization to recycling endosomes; this is not a patient-tissue result.
    - reference: PMID:23125191
      reference_title: Targeting C4-demethylating genes in the cholesterol pathway sensitizes cancer cells to EGF receptor inhibitors via increased EGF receptor degradation.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: The reduced intracellular EGFR staining was accompanied by a marked loss of phosphorylated (activated) Y1173-EGFR ... signal in the NSDHL-null areas.
      explanation: NSDHL-null patches of mouse skin had reduced activated EGFR; the original sentence also reports reduced ERK and AKT phosphorylation.
- name: Reduced EGFR Signaling
  description: NSDHL-null patches of mouse skin show reduced activated EGFR, ERK, and AKT signals with reduced proliferation and loricrin expression. These model observations suggest altered epidermal growth and differentiation, but do not demonstrate the same signaling state in patient skin.
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:23125191
    reference_title: Targeting C4-demethylating genes in the cholesterol pathway sensitizes cancer cells to EGF receptor inhibitors via increased EGF receptor degradation.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: The reduced intracellular EGFR staining was accompanied by a marked loss of phosphorylated (activated) Y1173-EGFR ... signal in the NSDHL-null areas.
    explanation: NSDHL-null patches of mouse skin had reduced activated EGFR; the original sentence also reports reduced ERK and AKT phosphorylation.
  - reference: PMID:23125191
    reference_title: Targeting C4-demethylating genes in the cholesterol pathway sensitizes cancer cells to EGF receptor inhibitors via increased EGF receptor degradation.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: The NSDHL-null areas of the skin also exhibited significantly reduced proliferation, as determined by Ki-67 ... expression and in vivo BrdU incorporation
    explanation: Mouse skin proliferation was reduced, so human hyperkeratosis must not be generalized into a universal increase in cellular proliferation.
- name: Impaired Anagen Hair Growth
  description: Bpa1H mouse skin has impaired postnatal anagen progression despite apparently normal early follicle morphology. In treated CHILD patients, improvement of the skin lesions did not restore hair growth. A specific Hedgehog-mediated explanation for the human hair phenotype remains an inference.
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:19631568
    reference_title: Developmental expression pattern of the cholesterogenic enzyme NSDHL and negative selection of NSDHL-deficient cells in the heterozygous Bpa(1H)/+ mouse.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: The mutant follicles were smaller and shorter than adjacent WT follicles and lacked hair shafts, consistent with defective anagen hair growth.
    explanation: Mouse mutant skin shows defective postnatal anagen growth; initial P2 follicle morphology was not grossly abnormal.
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: By 6 months, treated skin largely normalized, but did not grow hair
    explanation: Skin improvement and hair growth were distinct outcomes in two treated patients.
  downstream:
  - target: Alopecia of affected skin
    description: Defective follicle growth in Nsdhl mouse skin is consistent with the human failure of hair growth; the intervening human pathway has not been demonstrated.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:19631568
      reference_title: Developmental expression pattern of the cholesterogenic enzyme NSDHL and negative selection of NSDHL-deficient cells in the heterozygous Bpa(1H)/+ mouse.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: The mutant follicles were smaller and shorter than adjacent WT follicles and lacked hair shafts, consistent with defective anagen hair growth.
      explanation: Mouse mutant skin shows defective postnatal anagen growth; initial P2 follicle morphology was not grossly abnormal.
    - reference: PMID:21753784
      reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: By 6 months, treated skin largely normalized, but did not grow hair
      explanation: Skin improvement and hair growth were distinct outcomes in two treated patients.
phenotypes:
- category: Cutaneous
  name: Ichthyosiform nevus
  description: >-
    Inflammatory erythematous plaques with yellowish waxy scale usually appear at birth or in early infancy. Lesions can be patchy, follow Blaschko lines, or involve both sides. Many improve with age, while intertriginous lesions can persist and new lesions can arise later, including at sites of injury.
  phenotype_term:
    preferred_term: Ichthyosiform nevus
    term:
      id: HP:0010816
      label: Epidermal nevus
  evidence:
  - reference: PMID:21290788
    reference_title: "NSDHL-Related Disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      CHILD syndrome is characterized by unilateral distribution of ichthyosiform
      skin lesions and ipsilateral limb defects that range from shortening of the
      metacarpals and phalanges to absence of the entire limb.
    explanation: >-
      GeneReviews names the unilateral ichthyosiform lesion as a defining feature.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:24060582
    reference_title: "The role of abnormalities in the distal pathway of cholesterol synthesis in the Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects (CHILD) syndrome."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The CHILD syndrome skin is characterized by plaques topped by waxy scales
      and a variety of developmental defects in extracutaneous tissues,
      particularly limb hypoplasia or aplasia.
    explanation: >-
      Describes the characteristic morphology of the plaques.
    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Most of the skin lesions improve spontaneously, but some can cause lifelong morbidity. Lesions in the intertriginous areas tend to be more persistent; this is termed ptychotropism
    explanation: GeneReviews describes the variable natural history and persistence in body folds.
- category: Cutaneous
  name: Strict midline demarcation of skin lesions
  description: >-
    Skin lesions typically have a sharp boundary at the body midline. Limited lesions can follow Blaschko lines, and molecularly confirmed bilateral, almost symmetric involvement has been reported; bilateral involvement does not exclude CHILD syndrome.
  phenotype_term:
    preferred_term: strict midline demarcation of the cutaneous eruption
  evidence:
  - reference: PMID:10710235
    reference_title: "Mutations in the NSDHL gene, encoding a 3beta-hydroxysteroid dehydrogenase, cause CHILD syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      an inflammatory nevus with striking lateralization and strict midline
      demarcation, as well as ipsilateral hypoplasia of the body
    explanation: >-
      States the midline demarcation of the nevus, which is the claim this
      phenotype makes.
  - reference: PMID:7408908
    reference_title: "The CHILD syndrome. Congenital hemidysplasia with ichthyosiform erythroderma and limb defects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The syndrome is characterized by unilateral erythema and scaling, with a
      distinct demarcation in the middle of the trunk.
    explanation: >-
      The original delineation locates the demarcation anatomically, at the
      middle of the trunk.
  - reference: PMID:11907515
    reference_title: "A novel missense mutation of NSDHL in an unusual case of CHILD syndrome showing bilateral, almost symmetric involvement."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A symmetric distribution of this nevus can exceptionally be seen in
      patients with CHILD syndrome, and this bilateral involvement should not
      mislead the clinician to any other diagnosis.
    explanation: >-
      Qualifies rather than supports the lateralization claim, documenting the
      exception that makes midline demarcation typical but not obligatory.
- category: Skeletal
  name: Ipsilateral body hypoplasia
  description: >-
    Hemidysplasia, the H in the acronym: hypoplasia of one side of the body, involving skeletal structures and internal organs on the same side as the cutaneous eruption. This is the body-growth asymmetry, distinct from both the distribution of the skin lesion and the limb-specific defect below.
  phenotype_term:
    preferred_term: Asymmetric growth
    term:
      id: HP:0100555
      label: Asymmetric growth
  evidence:
  - reference: PMID:10710235
    reference_title: "Mutations in the NSDHL gene, encoding a 3beta-hydroxysteroid dehydrogenase, cause CHILD syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      an inflammatory nevus with striking lateralization and strict midline
      demarcation, as well as ipsilateral hypoplasia of the body
    explanation: >-
      States the ipsilateral hypoplasia of the body, which is the asymmetric
      growth this term describes.
  - reference: PMID:7408908
    reference_title: "The CHILD syndrome. Congenital hemidysplasia with ichthyosiform erythroderma and limb defects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In addition, ipsilateral hypoplasia of other parts of the skeleton, as well
      as defects of the brain and the viscera are found.
    explanation: >-
      Extends the ipsilateral hypoplasia beyond the limbs to the rest of the
      skeleton and the viscera.

- category: Skeletal
  name: Ipsilateral limb hypoplasia or aplasia
  description: >-
    Limb defects on the same side as the skin lesions, ranging in severity from shortening of metacarpals and phalanges through to absence of the entire limb. Severe cases have required amputation of a rudimentary limb in early childhood to permit prosthetic fitting.
  phenotype_term:
    preferred_term: Aplasia/hypoplasia involving bones of the extremities
    term:
      id: HP:0045060
      label: Aplasia/hypoplasia involving bones of the extremities
  evidence:
  - reference: PMID:21290788
    reference_title: "NSDHL-Related Disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      unilateral distribution of ichthyosiform skin lesions and ipsilateral limb
      defects that range from shortening of the metacarpals and phalanges to
      absence of the entire limb
    explanation: >-
      GeneReviews states the ipsilateral limb defect and its severity range as a
      defining characteristic.

    quote_role: REVIEW_SYNTHESIS
- category: Cutaneous
  name: Onychodystrophy and periungual hyperkeratosis
  description: >-
    Nail dystrophy and periungual hyperkeratosis are common. In the two-patient topical lovastatin/cholesterol report, one patient had little nail improvement despite improvement in the skin lesions.
  phenotype_term:
    preferred_term: Nail dystrophy
    term:
      id: HP:0008404
      label: Nail dystrophy
  evidence:
  - reference: PMID:21290788
    reference_title: "NSDHL-Related Disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Onychodystrophy and periungual hyperkeratosis are common.
    explanation: >-
      GeneReviews describes both findings as common without providing a denominator for a numerical frequency.

    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: She has improved digital mobility, but little improvement in onychodystrophy, likely reflecting the inability of the compound to penetrate the nail.
    explanation: One treated patient had persistent nail dystrophy; impaired penetration was the authors' proposed explanation.
- category: Cutaneous
  name: Alopecia of affected skin
  description: >-
    Alopecia can involve affected skin or the ipsilateral scalp. Hair did not regrow in the two patients whose skin otherwise improved with topical lovastatin/cholesterol; that observation does not establish the developmental signaling mechanism in human follicles.
  phenotype_term:
    preferred_term: Alopecia
    term:
      id: HP:0001596
      label: Alopecia
  evidence:
  - reference: PMID:21753784
    reference_title: "Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      By 6 months, treated skin largely normalized, but did not grow hair
    explanation: >-
      Reports the persistence of alopecia despite otherwise successful treatment.

- category: Skeletal
  name: Stippled epiphyseal calcification
  description: >-
    Unilateral punctate calcifications of cartilage can be visible on radiographs in infancy, usually in affected limbs or body regions. Their disappearance by age two was reported in one child; it is not known whether stippling always resolves.
  phenotype_term:
    preferred_term: Stippled chondral calcification
    term:
      id: HP:0002764
      label: Stippled chondral calcification
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Unilateral punctate epiphyseal calcifications (chondrodysplasia punctata) in the pelvis, ribs, vertebrae, and extremities have been reported and are usually seen in the affected limb or body part.
    explanation: GeneReviews describes the distribution of punctate calcifications in CHILD syndrome.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: In one child, the punctate calcifications were reported to have disappeared completely by age two years ... it is not known whether stippling always disappears.
    explanation: The review limits evidence for disappearance to one reported child.
- category: Skeletal
  name: Scoliosis
  description: >-
    Scoliosis can accompany the skeletal abnormalities. Severe lumbar scoliosis was documented in one of the two patients in the original topical lovastatin/cholesterol study.
  phenotype_term:
    preferred_term: Scoliosis
    term:
      id: HP:0002650
      label: Scoliosis
  evidence:
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: The patient also had neurosensory deafness of the right ear and severe lumbar scoliosis.
    explanation: The primary report directly documents scoliosis and hearing loss in a molecularly confirmed patient.
- name: Cardiac septal defect
  category: Cardiovascular
  description: Septal heart defects have been reported; the GeneReviews summary does not specify an atrial or ventricular subtype. Visceral involvement can occur on the same side as the skin lesions in the classic presentation; lateralization is not obligatory in every patient.
  phenotype_term:
    preferred_term: Abnormal cardiac septum morphology
    term:
      id: HP:0001671
      label: Abnormal cardiac septum morphology
    coarse_binding_basis: SOURCE_UNSPECIFIED
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Heart defects include septal defects
    explanation: The source supports a septal defect without identifying its chamber location.
  - reference: PMID:11907515
    reference_title: A novel missense mutation of NSDHL in an unusual case of CHILD syndrome showing bilateral, almost symmetric involvement.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney.
    explanation: The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.
- name: Hydronephrosis
  category: Renal
  description: Unilateral hydronephrosis is part of the reported renal spectrum. Visceral involvement can occur on the same side as the skin lesions in the classic presentation; lateralization is not obligatory in every patient.
  phenotype_term:
    preferred_term: Hydronephrosis
    term:
      id: HP:0000126
      label: Hydronephrosis
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Renal manifestations range from unilateral hydronephrosis to renal agenesis. The frequency of these is unknown.
    explanation: GeneReviews identifies these renal findings while explicitly leaving their frequencies unknown.
  - reference: PMID:11907515
    reference_title: A novel missense mutation of NSDHL in an unusual case of CHILD syndrome showing bilateral, almost symmetric involvement.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney.
    explanation: The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.
- name: Renal agenesis
  category: Renal
  description: Renal agenesis has been reported; its frequency is unknown. Visceral involvement can occur on the same side as the skin lesions in the classic presentation; lateralization is not obligatory in every patient.
  phenotype_term:
    preferred_term: Renal agenesis
    term:
      id: HP:0000104
      label: Renal agenesis
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Renal manifestations range from unilateral hydronephrosis to renal agenesis. The frequency of these is unknown.
    explanation: GeneReviews identifies these renal findings while explicitly leaving their frequencies unknown.
  - reference: PMID:11907515
    reference_title: A novel missense mutation of NSDHL in an unusual case of CHILD syndrome showing bilateral, almost symmetric involvement.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney.
    explanation: The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.
- name: Pulmonary hypoplasia
  category: Respiratory
  description: Pulmonary hypoplasia can cause respiratory compromise and death. Visceral involvement can occur on the same side as the skin lesions in the classic presentation; lateralization is not obligatory in every patient.
  phenotype_term:
    preferred_term: Pulmonary hypoplasia
    term:
      id: HP:0002089
      label: Pulmonary hypoplasia
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Lung hypoplasia has been observed in several individuals ... and can cause respiratory compromise and death
    explanation: GeneReviews identifies the specific pulmonary malformation and its potential severity.
  - reference: PMID:11907515
    reference_title: A novel missense mutation of NSDHL in an unusual case of CHILD syndrome showing bilateral, almost symmetric involvement.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney.
    explanation: The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.
- category: Musculoskeletal
  name: Joint contracture
  description: >-
    Joint contractures occur with the skeletal involvement and, like scoliosis, are managed with bracing or corrective surgery and tracked on surveillance.
  phenotype_term:
    preferred_term: Joint contracture
    term:
      id: HP:0034392
      label: Joint contracture
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Joint contractures are reported. Oligodactyly can be seen; polydactyly and syndactyly have been rarely reported.
    explanation: GeneReviews lists contractures among the limb findings.
- name: Unilateral brain hypoplasia
  category: Neurologic
  description: Unilateral brain underdevelopment is among the reported structural anomalies. Intellectual function is usually normal in CHILD syndrome. Visceral involvement can occur on the same side as the skin lesions in the classic presentation; lateralization is not obligatory in every patient.
  phenotype_term:
    preferred_term: Unilateral brain hypoplasia
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CNS anomalies include unilateral hypoplasia or underdevelopment of the brain, lissencephaly type II, and cerebellar malformation
    explanation: The CHILD-specific clinical section lists these structural brain abnormalities; they are not imported from the separate CK syndrome section.
  - reference: PMID:11907515
    reference_title: A novel missense mutation of NSDHL in an unusual case of CHILD syndrome showing bilateral, almost symmetric involvement.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney.
    explanation: The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.
- name: Type II lissencephaly
  category: Neurologic
  description: Type II lissencephaly has been reported among the CNS malformations. Visceral involvement can occur on the same side as the skin lesions in the classic presentation; lateralization is not obligatory in every patient.
  phenotype_term:
    preferred_term: Type II lissencephaly
    term:
      id: HP:0007260
      label: Type II lissencephaly
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CNS anomalies include unilateral hypoplasia or underdevelopment of the brain, lissencephaly type II, and cerebellar malformation
    explanation: The CHILD-specific clinical section lists these structural brain abnormalities; they are not imported from the separate CK syndrome section.
  - reference: PMID:11907515
    reference_title: A novel missense mutation of NSDHL in an unusual case of CHILD syndrome showing bilateral, almost symmetric involvement.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney.
    explanation: The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.
- name: Cerebellar malformation
  category: Neurologic
  description: Cerebellar malformation is reported without a more specific morphology in the GeneReviews summary. Visceral involvement can occur on the same side as the skin lesions in the classic presentation; lateralization is not obligatory in every patient.
  phenotype_term:
    preferred_term: Abnormal cerebellum morphology
    term:
      id: HP:0001317
      label: Abnormal cerebellum morphology
    coarse_binding_basis: SOURCE_UNSPECIFIED
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CNS anomalies include unilateral hypoplasia or underdevelopment of the brain, lissencephaly type II, and cerebellar malformation
    explanation: The CHILD-specific clinical section lists these structural brain abnormalities; they are not imported from the separate CK syndrome section.
  - reference: PMID:11907515
    reference_title: A novel missense mutation of NSDHL in an unusual case of CHILD syndrome showing bilateral, almost symmetric involvement.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney.
    explanation: The report summarizes the ipsilateral skeletal and visceral pattern of classic CHILD syndrome; it does not imply that every defect or every patient is unilateral.
- name: Sensorineural hearing loss
  category: Auditory
  description: Ipsilateral sensorineural hearing loss was documented in a molecularly confirmed adult.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: The patient also had neurosensory deafness of the right ear and severe lumbar scoliosis.
    explanation: The primary case report establishes the sensorineural subtype and laterality for this individual.
- name: Oligodactyly
  category: Skeletal
  description: Reduced digit number is part of the limb spectrum.
  phenotype_term:
    preferred_term: Oligodactyly
    term:
      id: HP:0012165
      label: Oligodactyly
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Oligodactyly can be seen; polydactyly and syndactyly have been rarely reported.
    explanation: GeneReviews describes reduced digit number and occasional additional or fused digits without a numerical denominator.
- name: Polydactyly
  category: Skeletal
  description: Additional digits have occasionally been reported.
  phenotype_term:
    preferred_term: Polydactyly
    term:
      id: HP:0010442
      label: Polydactyly
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Oligodactyly can be seen; polydactyly and syndactyly have been rarely reported.
    explanation: GeneReviews describes reduced digit number and occasional additional or fused digits without a numerical denominator.
- name: Syndactyly
  category: Skeletal
  description: Fused digits have occasionally been reported.
  phenotype_term:
    preferred_term: Syndactyly
    term:
      id: HP:0001159
      label: Syndactyly
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Oligodactyly can be seen; polydactyly and syndactyly have been rarely reported.
    explanation: GeneReviews describes reduced digit number and occasional additional or fused digits without a numerical denominator.
- name: Optic atrophy
  category: Ophthalmologic
  description: Bilateral optic atrophy was reported in one individual summarized by GeneReviews.
  phenotype_term:
    preferred_term: Optic atrophy
    term:
      id: HP:0000648
      label: Optic atrophy
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Bilateral optic atrophy has been reported in one individual
    explanation: The source establishes a reported finding, not a population frequency.
- name: Unilateral vocal cord paralysis
  category: Respiratory
  description: Ipsilateral vocal cord paralysis has been reported.
  phenotype_term:
    preferred_term: Unilateral vocal cord paralysis
    term:
      id: HP:0008757
      label: Unilateral vocal cord paralysis
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Ipsilateral vocal cord paralysis and liver lobe and spleen hypertrophy have been reported
    explanation: The source lists ipsilateral vocal cord paralysis as an additional finding.
- name: Gastrointestinal mucosal xanthomas
  category: Gastrointestinal
  description: Mucosal xanthomas can involve the upper gastrointestinal tract. In one adult, plaques in the distal oesophagus, stomach and duodenum contained CD163-positive macrophages; this case does not establish their frequency.
  phenotype_term:
    preferred_term: Gastrointestinal mucosal xanthomas
  evidence:
  - reference: PMID:34957706
    reference_title: A novel NSDHL variant in CHILD syndrome with gastrointestinal manifestations and localized skin involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: An esophagogastroduodenoscopy revealed multiple whitish plaques in the proximal duodenum, stomach and distal oesophagus ... Biopsies of these areas showed similar xanthoma cells with finely vacuolated cytoplasm in the lamina propria
    explanation: A molecularly confirmed adult had gastrointestinal mucosal xanthomas demonstrated by endoscopy and biopsy.
prevalence:
- population: Published cases summarized in GeneReviews, September 2024
  measure_type: CASES_IN_LITERATURE
  notes: >-
    GeneReviews reported more than 60 individuals in its September 2024 update and stated that prevalence is unknown. This historical literature count is neither a current total nor a population prevalence estimate.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: The prevalence of CHILD syndrome is unknown; more than 60 individuals have been reported to date.
    explanation: The source reports a literature count while explicitly stating that population prevalence is unknown.
histopathology:
- name: Psoriasiform hyperkeratosis and acanthosis with loss of the granular layer
  description: >-
    Lesional skin shows marked hyperkeratosis and acanthosis with absence of the
    granular layer, together with foam cells in the dermis. This is the routine
    light-microscopic picture, and it reverses on effective pathogenesis-based
    therapy: after three months of topical cholesterol plus lovastatin the
    epidermis was largely normal with a prominent granular layer and
    orthokeratotic scale.
  finding_term:
    preferred_term: hyperkeratosis with acanthosis
    term:
      id: NCIT:C35541
      label: Hyperkeratosis
  evidence:
  - reference: PMID:21753784
    reference_title: "Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Baseline biopsy sections of skin lesions from both patients prior to
      treatment showed marked hyperkeratosis and acanthosis with absence of the
      granular layer and dermal foam cells
    explanation: >-
      Reports the light-microscopic findings in lesional skin from both patients,
      including the dermal foam cells.

- name: Verruciform xanthoma-like change in the CHILD nevus
  description: >-
    Verruciform xanthoma-like histology can occur in the CHILD nevus, together with psoriasiform changes. It is not specific enough to establish the diagnosis by itself. A prominent vulvar and inner-thigh lesion required debulking in one patient in the topical-treatment report.
  diagnostic: false
  finding_term:
    preferred_term: verruciform xanthoma-like change
  evidence:
  - reference: PMID:7640190
    reference_title: "Epidermal nevus syndromes."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The associated CHILD nevus shows unique features such as a diffuse form of
      lateralization, ptychotropism, and microscopic changes of verruciform
      xanthoma.
    explanation: >-
      The review describes verruciform xanthoma-like changes in CHILD nevi; the finding is not diagnostic by itself.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:16776722
    reference_title: "Abnormal lamellar granules in a case of CHILD syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The histology shared many features with verruciform xanthoma.
    explanation: >-
      Independent case confirmation of the verruciform xanthoma resemblance.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: this is a nonspecific histopathologic finding that can be seen in other entities but may help distinguish CHILD nevi from other psoriasiform lesions on histopathology.
    explanation: GeneReviews explicitly limits the specificity of verruciform xanthoma-like histology.
- name: Abnormal lamellar granules on electron microscopy
  description: >-
    Ultrastructurally the lesion is a lipid secretory failure. Vesicular
    structures appear in the intercellular spaces of the stratum corneum and
    vacuoles in the upper prickle cell layer, some recognizable as abnormal
    lamellar granules, with large vacuoles inside the foamy cells of the
    papillary dermis. This is the electron-microscopic counterpart of the
    lamellar body secretory defect modelled in the pathophysiology, observed in
    a separate patient and laboratory from the treatment study.
  finding_term:
    preferred_term: abnormal epidermal lamellar granules
  evidence:
  - reference: PMID:16776722
    reference_title: "Abnormal lamellar granules in a case of CHILD syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These findings suggested that abnormal lipid metabolism involving lamellar
      granules may be responsible to the skin lesion of CHILD syndrome.
    explanation: >-
      States the authors' interpretation linking the ultrastructural finding to
      the lipid-metabolic lesion, preserving the hedged form they used.
- name: Gastrointestinal mucosal xanthomatous infiltrates
  description: Upper gastrointestinal biopsies in a molecularly confirmed adult showed finely vacuolated xanthoma cells in the lamina propria, positive for the macrophage marker CD163.
  finding_term:
    preferred_term: mucosal xanthomatous infiltrates
  diagnostic: false
  evidence:
  - reference: PMID:34957706
    reference_title: A novel NSDHL variant in CHILD syndrome with gastrointestinal manifestations and localized skin involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: An esophagogastroduodenoscopy revealed multiple whitish plaques in the proximal duodenum, stomach and distal oesophagus ... Biopsies of these areas showed similar xanthoma cells with finely vacuolated cytoplasm in the lamina propria
    explanation: A molecularly confirmed adult had gastrointestinal mucosal xanthomas demonstrated by endoscopy and biopsy.
  - reference: PMID:34957706
    reference_title: A novel NSDHL variant in CHILD syndrome with gastrointestinal manifestations and localized skin involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: These cells were positive for CD163 stain ... confirming their macrophage lineage and the diagnosis of gastrointestinal xanthomatosis.
    explanation: Immunostaining identifies the mucosal xanthoma cells as macrophages.
progression:
- phase: Postnatal improvement of cutaneous lesions
  notes: >-
    Cutaneous lesions can improve with age, but intertriginous lesions may persist and new lesions can arise later, including at sites of injury.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Most of the skin lesions improve spontaneously, but some can cause lifelong morbidity. Lesions in the intertriginous areas tend to be more persistent; this is termed ptychotropism
    explanation: GeneReviews describes the human cutaneous course.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Ichthyosiform skin lesions can develop after infancy at sites of injury such as a surgical wound.
    explanation: Lesions can also appear after early development.
- phase: Survival into adulthood
  notes: Life span in females is not well characterized. Adults with a wide range of disease severity have been reported, including an individual diagnosed at age 82; that observation does not establish a normal population life expectancy. Pulmonary hypoplasia can cause early respiratory compromise and death.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: It is unknown whether life span in females with CHILD syndrome is abnormal.
    explanation: GeneReviews explicitly states uncertainty about life expectancy.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CHILD syndrome was reported with phenotypes ranging from mild to severe in three different generations, with the oldest reported individual clinically and molecularly diagnosed at age 82 years
    explanation: The source documents survival to old age in a family, not a population survival estimate.
biochemical:
- name: Methylsterol accumulation in affected tissue
  presence: INCREASED
  notes: >-
    C4-methylsterol intermediates can accumulate in affected tissue. Plasma profiles can be near normal and therefore cannot exclude NSDHL-related disease. A reported p.Gly44Ser case had a characteristic skin-flake sterol profile with an abnormal sterol also detectable in plasma. EBP-related CDPX2 has a different sterol signature and is a differential diagnosis.
  evidence:
  - reference: PMID:24060582
    reference_title: "The role of abnormalities in the distal pathway of cholesterol synthesis in the Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects (CHILD) syndrome."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      which leads to inhibition of cholesterol synthesis and accumulation of toxic
      metabolic intermediates in affected tissues
    explanation: >-
      States the accumulation of intermediates and localizes it to affected
      tissues rather than the circulation.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:10369263
    reference_title: "The gene mutated in bare patches and striated mice encodes a novel 3beta-hydroxysteroid dehydrogenase."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Quantitative analysis of sterols from tissues of affected Bpa mice support a
      role for Nsdhl in cholesterol biosynthesis.
    explanation: >-
      Reports the tissue sterol measurements in the mouse counterpart of the
      disorder.

diagnosis:
- name: NSDHL molecular genetic testing
  description: >-
    Diagnosis is supported by characteristic findings and a pathogenic or likely pathogenic NSDHL variant. Sequence analysis detects many coding and splice variants, while exon-level deletion/duplication analysis is needed for copy-number variants that conventional sequencing can miss. A variant of uncertain significance neither establishes nor excludes the diagnosis. Rare mosaic males and mild females require clinical and molecular interpretation rather than exclusion by sex or by absence of a severe limb defect. Optical genome mapping has been reported in a mixed cohort of incontinentia pigmenti and CHILD syndrome; this does not establish a general diagnostic yield for CHILD syndrome.
  diagnosis_term:
    preferred_term: Genetic Testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:21290788
    reference_title: "NSDHL-Related Disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The diagnosis of CHILD syndrome is established in a female proband with a
      heterozygous NSDHL pathogenic variant identified by molecular genetic
      testing that results in loss of functional decarboxylating
      sterol-4-alpha-carboxylate 3-dehydrogenase, the protein encoded by NSDHL.
    explanation: >-
      GeneReviews states the diagnostic criterion.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:29341259
    reference_title: "CHILD syndrome mimicking verrucous nevus in a Chinese patient responded well to the topical therapy of compound of simvastatin and cholesterol."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Multiple exons deletions or microdeletion was not rare in CHILD syndrome.
      Classical Sanger sequencing may not be useful enough to find all kinds of
      mutations. Next-generation sequencing may be more effective.
    explanation: >-
      States the assay blind spot directly, and the same report supplies the
      worked example, a large deletion of NSDHL exons 3 and 4.
  - reference: PMID:41625319
    reference_title: "Diagnostic Utility of Optical Genome Mapping in X-Linked Dominant Genodermatoses: Incontinentia Pigmenti and CHILD Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The identified structural variants consisted of deletions of varying sizes
      in the Xq28 cytoband, encompassing regions that contain exons.
    explanation: >-
      The abstract reports structural variants in a mixed incontinentia pigmenti/CHILD cohort. It does not assign every deletion to NSDHL or establish a CHILD-specific diagnostic yield.

  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Identification of a heterozygous or hemizygous NSDHL variant of uncertain significance does not establish or rule out the diagnosis.
    explanation: GeneReviews explicitly distinguishes a VUS from a diagnostic pathogenic variant.
- name: Sterol profiling of skin flakes and plasma
  description: >-
    Sterol profiling of affected skin can support biochemical interpretation of an NSDHL variant. In one p.Gly44Ser case, skin-flake methyl-, carboxy- and keto-sterol abnormalities supported reclassification from uncertain significance to likely pathogenic. An abnormal methylsterol was also detected in plasma in that patient. Serum profiles can be near normal, so a normal systemic result does not exclude the disorder.
  diagnosis_term:
    preferred_term: Diagnostic Procedure
    term:
      id: NCIT:C18020
      label: Diagnostic Procedure
  evidence:
  - reference: PMID:33139364
    reference_title: "Novel NSDHL gene variant for congenital hemidysplasia with ichthyosiform erythroderma and limb defects (CHILD) syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sterol analysis from skin flakes revealed increased levels of a mono
      4-alpha methyl sterol also seen in plasma as well as the presence of
      4-alpha-carboxy-4-methyl-cholest-8(9)-en-3beta-ol and several keto-sterols,
      which are usually below the limit of detection. This sterol pattern is
      consistent with abnormal function of the 4-alpha-methylsterol-4-demethylase
      complex.
    explanation: >-
      Reports the sterol pattern and its interpretation as evidence of the
      enzymatic block.
  - reference: PMID:33139364
    reference_title: "Novel NSDHL gene variant for congenital hemidysplasia with ichthyosiform erythroderma and limb defects (CHILD) syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      On this basis, this variant has been reclassified as likely pathogenic.
    explanation: >-
      Documents the concrete diagnostic use of the sterol result, resolving a
      variant of uncertain significance.

  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Serum concentrations of methylsterol and cholesterol are almost always normal in individuals with CHILD syndrome and CK syndrome.
    explanation: GeneReviews limits the usefulness of normal serum sterols for excluding these disorders.
treatments:
- name: Topical Cholesterol plus Statin (Pathogenesis-Based Therapy)
  description: >-
    Topical lovastatin or simvastatin combined with cholesterol has improved cutaneous lesions in uncontrolled reports. In the original two-patient study, 10% cholesterol alone produced no improvement over three months, followed by substantial improvement with 2% lovastatin/2% cholesterol. There was no statin-only arm, so this sequence does not establish that cholesterol supplementation is required. Later reports describe benefit from statin monotherapy. Skin improvement does not establish correction of congenital skeletal defects, and long-term comparative efficacy and safety remain uncertain.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: cholesterol
      term:
        id: CHEBI:16113
        label: cholesterol
    - preferred_term: lovastatin
      term:
        id: CHEBI:40303
        label: lovastatin
    - preferred_term: simvastatin
      term:
        id: CHEBI:9150
        label: simvastatin
  target_mechanisms:
  - target: Reduced Cholesterol Availability
    treatment_effect: RESTORES
    description: The cholesterol component supplies the pathway end product; tissue-specific target engagement was not isolated from the effects of the statin in the clinical report.
    evidence:
    - reference: PMID:21753784
      reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: INDIRECT
      snippet: On the basis of the putative pathogenic role of both pathway-product deficiency of cholesterol and accumulation of toxic metabolic intermediates, we assessed the efficacy of combined therapy with lovastatin and cholesterol.
      explanation: The authors state the dual treatment rationale as putative. The combined intervention does not isolate restoration of cholesterol from suppression of precursor formation.
  - target: C4-Methylsterol Accumulation
    treatment_effect: INHIBITS
    description: Upstream statin inhibition is intended to reduce precursor production; clinical response to the combination is consistent with this rationale but does not quantify precursor clearance.
    evidence:
    - reference: PMID:21753784
      reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: INDIRECT
      snippet: On the basis of the putative pathogenic role of both pathway-product deficiency of cholesterol and accumulation of toxic metabolic intermediates, we assessed the efficacy of combined therapy with lovastatin and cholesterol.
      explanation: The authors state the dual treatment rationale as putative. The combined intervention does not isolate restoration of cholesterol from suppression of precursor formation.
  evidence:
  - reference: PMID:21753784
    reference_title: "Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Topical treatment with lovastatin/cholesterol (but not cholesterol alone)
      virtually cleared skin lesions by 3 months, accompanied by histological and
      ultrastructural normalization of epidermal structure and lipid secretion.
    explanation: >-
      Cholesterol alone did not improve the lesions in this two-patient sequence; there was no statin-only comparison to establish that the combination is required.
  - reference: PMID:25845514
    reference_title: "CHILD Syndrome: Successful Treatment of Skin Lesions with Topical Simvastatin/Cholesterol Ointment--A Case Report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We report the case of a 10-year-old girl treated with topical simvastatin
      and cholesterol ointment, after which her skin lesions significantly improved
      within the first 30 days of treatment.
    explanation: >-
      Independent case replication using simvastatin in place of lovastatin.
  - reference: PMID:31365666
    reference_title: "CHILD syndrome: successful treatment of skin lesions with topical lovastatin and cholesterol lotion."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The authors report a 2-month-old patient presenting with typical features of
      CHILD syndrome that was treated with a topical solution containing
      cholesterol and lovastatin, with complete clearance of her CHILD nevus.
    explanation: >-
      An additional infant case had clearance of the nevus with the combination.

  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Decreased inflammation, skin thickening, and scaling was noted as early as 4–6 weeks in both patients, and the severity scores decreased by 72% (patient 1) and 79% (patient 2) by 3 months.
    explanation: The uncontrolled two-patient study reports separate within-patient severity-score reductions, not comparative efficacy.
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: We first addressed the possibility that skin lesions in CHILD syndrome primarily reflect cholesterol (pathway end-product) deficiency alone, but found no clinical improvement after 3 months of treatment with twice daily topical 10% cholesterol in hydrophilic ointment.
    explanation: This sequential observation argues against cholesterol-alone efficacy in the two patients; no statin-only arm tested the necessity of supplementation.
  - reference: PMID:32886633
    reference_title: Topical Cholesterol/Simvastatin Gel for the Treatment of CHILD Syndrome in an Adolescent.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Herein, we report a case of successful treatment of the cutaneous features of CHILD syndrome with compounded simvastatin and cholesterol gel and highlight the role of the compounding pharmacist in the care of patients with congenital ichthyosis.
    explanation: An additional uncontrolled case report describes cutaneous benefit with compounded simvastatin/cholesterol gel.
- name: Topical Simvastatin Monotherapy
  description: Uncontrolled reports describe improvement with topical simvastatin without added cholesterol. In an infant treated with 2% ointment twice daily, improvement appeared by three weeks and the skin largely normalized by six weeks, with maintenance treatment over ten months. A later 5% report describes variable responses by site and recurrent lesions; it follows the previously reported p.Gly44Ser patient rather than adding an independent genotype case. Comparative efficacy and long-term safety are not established.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: simvastatin
      term:
        id: CHEBI:9150
        label: simvastatin
  evidence:
  - reference: PMID:29687057
    reference_title: 'Pathogenesis-based therapy: Cutaneous abnormalities of CHILD syndrome successfully treated with topical simvastatin monotherapy.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: After obtaining informed consent from her father, we began treatment with twice-daily topical simvastatin 2% ointment
    explanation: The primary case used simvastatin monotherapy.
  - reference: PMID:29687057
    reference_title: 'Pathogenesis-based therapy: Cutaneous abnormalities of CHILD syndrome successfully treated with topical simvastatin monotherapy.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Decreased inflammation, skin thickening, and scaling were noted as early as 3 weeks. By 6 weeks, the treated skin largely and dramatically normalized with a discrete postinflammatory hypopigmentation remaining
    explanation: Clinical results describe improvement by three weeks and near-normalization at six weeks.
  - reference: PMID:29687057
    reference_title: 'Pathogenesis-based therapy: Cutaneous abnormalities of CHILD syndrome successfully treated with topical simvastatin monotherapy.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: No reoccurrence was observed after 10 months of maintenance topical treatment
    explanation: Continued maintenance accompanied the reported sustained response.
  - reference: PMID:39431262
    reference_title: '5% Simvastatin Ointment as Treatment for Congenital Hemidysplasia with Ichthyosiform Erythroderma and Limb Defects (CHILD) Syndrome in a 4-year-old Female: A Case Report.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: However, the verrucous plaques reappeared on the palms on week 12, which again almost cleared after four weeks. The most responsive sites were the arm, chest, abdomen, inguinal and labia majora, while the foot was the most resistant.
    explanation: The follow-up report shows site-dependent response and recurrence rather than universal clearance.
  - reference: PMID:39431262
    reference_title: '5% Simvastatin Ointment as Treatment for Congenital Hemidysplasia with Ichthyosiform Erythroderma and Limb Defects (CHILD) Syndrome in a 4-year-old Female: A Case Report.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Monitoring of liver and kidney function tests, as well as serum cholesterol level were not done, similar to previously-published cases.
    explanation: Absence of reported acute adverse effects in this case does not establish laboratory or long-term safety.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Simvastatin was ↑ from 2.5% to 5% to enhance effectiveness of treatment.
    explanation: GeneReviews summarizes dose escalation reported by Yu et al.; this secondary statement does not establish a preferred concentration.
- name: Topical Ketoconazole
  description: Off-label topical 2% ketoconazole has improved cutaneous lesions in individual reports. In one adult using it twice daily, itch improved after two days, erythema and scaling improved by day seven, and lesions were substantially improved by day 40. DLQI decreased from 3 to 1, with no apparent adverse effects during two and a half months of follow-up. This uncontrolled observation does not establish equivalence to statins or durable remission after stopping treatment.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: ketoconazole
      term:
        id: CHEBI:47519
        label: ketoconazole
  evidence:
  - reference: PMID:39565229
    reference_title: Improvement of Skin Lesions in an Adult with CHILD Syndrome Treated with 2% Ketoconazole Cream.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Institutional approval was obtained for the off-label use of 2% ketoconazole cream. The pre-treatment Dermatology Life Quality Index (DLQI) score was 3 out of 30.
    explanation: The adult report specifies the off-label formulation and baseline quality-of-life score.
  - reference: PMID:39565229
    reference_title: Improvement of Skin Lesions in an Adult with CHILD Syndrome Treated with 2% Ketoconazole Cream.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: The itching improved after 2 days of treatment. At 7 days after the start of the treatment, the area of erythema was unchanged, but the desquamation had generally disappeared and the redness of the erythema had improved
    explanation: The clinical endpoints distinguish symptom improvement from the unchanged area at one week.
  - reference: PMID:39565229
    reference_title: Improvement of Skin Lesions in an Adult with CHILD Syndrome Treated with 2% Ketoconazole Cream.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: At 40 days of treatment, the skin lesions had significantly improved, with only minimal pigmentation.
    explanation: The report describes substantial improvement by day 40.
  - reference: PMID:39565229
    reference_title: Improvement of Skin Lesions in an Adult with CHILD Syndrome Treated with 2% Ketoconazole Cream.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: On day 40, the DLQI score was 1.
    explanation: The reported quality-of-life score improved from baseline.
  - reference: PMID:39565229
    reference_title: Improvement of Skin Lesions in an Adult with CHILD Syndrome Treated with 2% Ketoconazole Cream.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: We followed the patient for a total of 2½ months with no apparent side effects.
    explanation: The safety observation is limited to a single patient and short follow-up.
- name: Symptomatic Topical Care
  description: >-
    Lactic acid preparations can reduce itching and urea creams can help dry skin. Emollients, keratolytics and other topical anti-inflammatory treatments have had variable benefit in individual reports. GeneReviews also describes poorly tolerated or inconsistent responses to oral etretinate. These observations do not establish comparative efficacy.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Lactic acid 12% creams or lotions for itching
    explanation: GeneReviews lists symptomatic topical care for itch.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Urea creams for dry skin
    explanation: GeneReviews lists urea for dryness.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Oral aromatic retinoids (etretinate) may ameliorate cutaneous symptoms; however, this drug is often poorly tolerated ... & does not prove effective in every person.
    explanation: The review qualifies both tolerability and consistency of reported etretinate benefit.
- name: Skin Grafting from the Unaffected Side
  description: >-
    Grafting skin from the unaffected contralateral region has been successful in an individual report. GeneReviews also describes recurrence within eight months after dermabrasion; these sparse reports do not establish comparative surgical effectiveness.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Skin Transplantation
    term:
      id: NCIT:C15325
      label: Skin Transplantation
  target_mechanisms:
  - target: X-Inactivation-Dependent NSDHL Expression Mosaicism
    treatment_effect: BYPASSES
    description: >-
      Grafting replaces mutant-expressing epidermis with wild-type-expressing
      epidermis, bypassing rather than correcting the mosaic distribution.
    evidence:
    - reference: PMID:21290788
      reference_title: "NSDHL-Related Disorders."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Treatment of an inflammatory nevus by grafting skin obtained from a
        contralateral unaffected region has been successful.
      explanation: >-
        Reports the intervention and its dependence on an unaffected-side donor
        site, which is what makes it a mosaic-bypassing strategy.
      quote_role: REVIEW_SYNTHESIS
  evidence:
  - reference: PMID:21290788
    reference_title: "NSDHL-Related Disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Treatment of an inflammatory nevus by grafting skin obtained from a
      contralateral unaffected region has been successful.
    explanation: >-
      GeneReviews records grafting as an effective option for a localized
      inflammatory nevus.

    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Removal by dermabrasion was reported; however, it recurred w/in 8 mos.
    explanation: GeneReviews records recurrence after dermabrasion as a limitation of that separate procedure.
- name: Orthopedic and Rehabilitative Management of the Limb and Spine Defects
  description: >-
    Braces and corrective surgery are used for scoliosis and joint contractures. Prosthetic fitting and rehabilitation may be needed for severe limb reduction. In one reported patient, skin improvement permitted use of a prosthesis; this was a functional benefit without reversal of the congenital skeletal defect.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Orthopedic Surgical Procedure
    term:
      id: NCIT:C16186
      label: Orthopedic Surgical Procedure
  evidence:
  - reference: PMID:21290788
    reference_title: "NSDHL-Related Disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Scoliosis and joint contractures are treated with braces and/or corrective
      surgery.
    explanation: >-
      GeneReviews states the orthopedic management of the axial and joint
      deformities.

    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: 'Patient #1, now more than 1 year on therapy, uses the medication twice weekly with good control and is able to wear her prosthesis.'
    explanation: Improved skin tolerance enabled prosthesis use in this patient.
- name: Initial Multisystem Assessment and Surveillance
  description: >-
    GeneReviews recommends initial assessment of cutaneous, skeletal, neurologic, cardiac, pulmonary and renal involvement, including echocardiography, chest imaging and abdominal/pelvic ultrasound. Developmental assessment and neurologic evaluation address CNS manifestations. Subsequent monitoring for skin lesions, scoliosis, contractures and neurologic, cardiac or renal manifestations is annual or as needed, with relevant specialist care. These recommendations reflect the GeneReviews authors' experience rather than a formal clinical practice guideline.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:21290788
    reference_title: "NSDHL-Related Disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      In CHILD syndrome, monitor for new cutaneous lesions, musculoskeletal
      deformities such as scoliosis and joint contractures, and neurologic,
      cardiac, and/or kidney manifestations annually or as needed.
    explanation: >-
      GeneReviews states the surveillance schedule and the organ systems it
      covers.

    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Cardiac Echocardiogram Evaluate for congenital heart disease.
    explanation: The initial-evaluation table recommends echocardiography.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Pulmonary Chest imaging Evaluate for lung hypoplasia.
    explanation: The initial-evaluation table specifically addresses lung hypoplasia.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Genitourinary Abdominal & pelvic ultrasound Evaluate for renal or other genitourinary anomalies.
    explanation: The initial-evaluation table recommends renal and pelvic assessment.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: the following recommendations are based on the authors' personal experience managing individuals with CHILD syndrome and CK syndrome.
    explanation: GeneReviews identifies the basis of its management recommendations.
- name: Genetic Counseling
  description: >-
    Counseling addresses X-linked inheritance, a 50% transmission probability for a heterozygous mother, variable expression in females and the effect of usual hemizygous male lethality on live-born ratios. Once a familial pathogenic variant is identified, testing of relatives and prenatal or preimplantation testing are possible. A VUS alone does not establish a molecular diagnosis or a variant-specific recurrence risk.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:21290788
    reference_title: "NSDHL-Related Disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Once the NSDHL pathogenic variant has been identified in a family member
      with an NSDHL-related disorder, prenatal and preimplantation genetic testing
      are possible.
    explanation: >-
      States the reproductive testing options that counseling is built around.

    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK51754/pdf/Bookshelf_NBK51754.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: The chance of transmitting the pathogenic variant in each pregnancy is 50%.
    explanation: GeneReviews states the transmission probability for a heterozygous mother.
animal_models:
- name: Bare patches and striated mice (Nsdhl mutant)
  species: Mouse
  genotype: Nsdhl mutant alleles Bpa and Str, X-linked dominant male-lethal
  publication: PMID:10369263
  description: >-
    Bare patches and striated Nsdhl mice reproduce an X-linked sterol-biosynthesis defect and mosaic skin involvement. Several alleles cause prenatal male death at E10.5-E13.5, while the severe Bpa1H allele often causes earlier death. Age-related selection is measured in liver and brain; skin, placental, signaling, and hair findings require their own tissue and allele context. Patches and stripes do not reproduce the characteristic human body-half distribution.
  genes:
  - preferred_term: NSDHL
    term:
      id: hgnc:13398
      label: NSDHL
  evidence:
  - reference: PMID:10710235
    reference_title: "Mutations in the NSDHL gene, encoding a 3beta-hydroxysteroid dehydrogenase, cause CHILD syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      They provide animal models for the study of CHILD syndrome, a further human
      condition due to mutations in a gene of the cholesterol synthesis pathway.
    explanation: >-
      The human gene-discovery paper explicitly nominates these mouse mutants as
      models for CHILD syndrome, which is the model-level claim.
  modeled_mechanisms:
  - target: NSDHL Loss of Function
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Independent Bpa and Str alleles are mutations in Nsdhl, and tissue sterol
      analysis confirms the biosynthetic role.
    limitations: >-
      The mouse skin phenotype is patterned as patches and stripes rather than the
      lateralized, midline-demarcated distribution seen in humans, so the model is
      informative for the enzymatic lesion but not for the lateralization.
    readouts:
    - name: Tissue sterol profile in affected Bpa mice
      target: NSDHL Loss of Function
      direction: ALTERED
      interpretation: >-
        Tissue sterol profiles support the biosynthetic consequence of the genotype; they do not directly measure every mutant protein catalytic activity.
      evidence:
      - reference: PMID:10369263
        reference_title: "The gene mutated in bare patches and striated mice encodes a novel 3beta-hydroxysteroid dehydrogenase."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Quantitative analysis of sterols from tissues of affected Bpa mice
          support a role for Nsdhl in cholesterol biosynthesis.
        explanation: >-
          Reports the sterol measurement underlying this readout.
    evidence:
    - reference: PMID:10369263
      reference_title: "The gene mutated in bare patches and striated mice encodes a novel 3beta-hydroxysteroid dehydrogenase."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Here we report mutations in one of these genes, Nsdhl, encoding an NAD(P)H
        steroid dehydrogenase-like protein, in two independent Bpa and three
        independent Str alleles.
      explanation: >-
        Establishes that these mouse mutants carry lesions in the orthologous gene.
      quote_role: PRIMARY_RESULT
    model_scale: MOLECULAR
  - target: X-Inactivation-Dependent NSDHL Expression Mosaicism
    description: Heterozygous female mice show patches of NSDHL-positive and NSDHL-negative tissue.
    evidence:
    - reference: PMID:19631568
      reference_title: Developmental expression pattern of the cholesterogenic enzyme NSDHL and negative selection of NSDHL-deficient cells in the heterozygous Bpa(1H)/+ mouse.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Heterozygous Bpa(1H) females are mosaic for NSDHL expression due to normal random X-inactivation.
      explanation: The mouse model reproduces mosaic expression, while its pattern differs from human lateralization.
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: Mouse patches and stripes differ from a human body-half boundary; tissue X-inactivation and selection are context-dependent.
    fidelity: MODERATE
  - target: Age-Dependent Depletion of NSDHL-Deficient Cells
    description: Cross-sectional mouse age groups show a higher proportion of NSDHL-positive hepatocytes with age.
    evidence:
    - reference: PMID:19631568
      reference_title: Developmental expression pattern of the cholesterogenic enzyme NSDHL and negative selection of NSDHL-deficient cells in the heterozygous Bpa(1H)/+ mouse.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: These data suggest that the higher percentage of WT hepatocytes present in livers from older Bpa1H females is the cumulative result of postnatal differences in either the growth rate or survival of WT vs mutant hepatocytes.
      explanation: Cross-sectional age groups support selection in mouse liver while leaving differential survival versus proliferation unresolved.
    - reference: PMID:19631568
      reference_title: Developmental expression pattern of the cholesterogenic enzyme NSDHL and negative selection of NSDHL-deficient cells in the heterozygous Bpa(1H)/+ mouse.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: 'The average percentage of NSDHL positive hepatocytes in livers from six Bpa1H P6 females was 52 (SD: 5). Among six mutant livers at P25, the average percentage of NSDHL positive hepatocytes increased to 62 (SD: 9).'
      explanation: The comparison concerns different mouse age groups and liver tissue, not serial biopsies of human skin.
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: The quantitative comparison is in liver, with additional brain observations. Mutant skin remains at eight weeks; this is not evidence of longitudinal clearance in human skin.
    fidelity: MODERATE
  - target: Placental Labyrinth Dysmorphogenesis
    description: Nsdhl mouse alleles exhibit a thin labyrinth, reduced fetal vessels, and reduced trophoblast proliferation.
    evidence:
    - reference: PMID:15639195
      reference_title: Placental defects are associated with male lethality in bare patches and striated embryos deficient in the NAD(P)H Steroid Dehydrogenase-like (NSDHL) Enzyme.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Although no consistent anomalies were identified in affected male embryos themselves, the labyrinth layer of the fetal placenta was always thinner, with fewer fetal vessels and decreased proliferation of labyrinth trophoblast cells.
      explanation: Several mouse alleles show a placental structural phenotype associated with prenatal lethality; it does not establish the cause of every male loss or a human placental lesion.
    - reference: PMID:17028112
      reference_title: Analysis of Nsdhl-deficient embryos reveals a role for Hedgehog signaling in early placental development.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Further, affected placentas from mutant Nsdhl(Bpa-8H) male embryos demonstrate markedly decreased or no Ptch1-lacZ staining and no migration of Ihh expressing cells into the developing placenta.
      explanation: Placental reporter and cellular-distribution observations implicate Hedgehog signaling in this mouse allele.
    relationship: PARTIALLY_RECAPITULATES
    model_scale: TISSUE
    limitations: Placental findings and timing vary by allele. Rodent placental X-inactivation differs from humans, and human placental pathology has not been established.
    fidelity: MODERATE
  - target: Reduced EGFR Signaling
    description: NSDHL-null mouse skin has reduced activated EGFR and downstream signals with reduced proliferation.
    evidence:
    - reference: PMID:23125191
      reference_title: Targeting C4-demethylating genes in the cholesterol pathway sensitizes cancer cells to EGF receptor inhibitors via increased EGF receptor degradation.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: The reduced intracellular EGFR staining was accompanied by a marked loss of phosphorylated (activated) Y1173-EGFR ... signal in the NSDHL-null areas.
      explanation: NSDHL-null patches of mouse skin had reduced activated EGFR; the original sentence also reports reduced ERK and AKT phosphorylation.
    - reference: PMID:23125191
      reference_title: Targeting C4-demethylating genes in the cholesterol pathway sensitizes cancer cells to EGF receptor inhibitors via increased EGF receptor degradation.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: The NSDHL-null areas of the skin also exhibited significantly reduced proliferation, as determined by Ki-67 ... expression and in vivo BrdU incorporation
      explanation: Mouse skin proliferation was reduced, so human hyperkeratosis must not be generalized into a universal increase in cellular proliferation.
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: These are mouse skin observations. Similar signaling changes have not been demonstrated in human CHILD lesions, and they do not imply universal epidermal hyperproliferation.
    fidelity: MODERATE
  - target: Impaired Anagen Hair Growth
    description: Mutant mouse skin has impaired anagen growth despite apparently normal early follicle morphology.
    evidence:
    - reference: PMID:19631568
      reference_title: Developmental expression pattern of the cholesterogenic enzyme NSDHL and negative selection of NSDHL-deficient cells in the heterozygous Bpa(1H)/+ mouse.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: The mutant follicles were smaller and shorter than adjacent WT follicles and lacked hair shafts, consistent with defective anagen hair growth.
      explanation: Mouse mutant skin shows defective postnatal anagen growth; initial P2 follicle morphology was not grossly abnormal.
    relationship: PARTIALLY_RECAPITULATES
    model_scale: TISSUE
    limitations: The hair-cycle observations are murine; they do not establish a specific SHH defect in patient follicles.
    fidelity: MODERATE
- name: Conditional Nsdhl ablation in radial glia
  species: Mouse
  genotype: Nsdhl(tm1.1Hrm) conditional allele, GFAP-cre driver
  publication: PMID:25652406
  description: >-
    Exon-5 deletion driven by hGFAP-cre in radial-glial lineages begins during embryonic CNS development. Mutant males are live-born but develop ataxia and severe postnatal neurodegeneration; the reported animals died at P12-P20. The model establishes consequences of tissue-specific NSDHL loss, not the clinical phenotype of a particular human CK hypomorphic allele. Isolated granule-cell rescue experiments are recorded separately as cell-culture models.
  genes:
  - preferred_term: NSDHL
    term:
      id: hgnc:13398
      label: NSDHL
  evidence:
  - reference: PMID:25652406
    reference_title: "Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Since hemizygous male mice with Nsdhl mutations die by midgestation, we
      generated a conditional targeted Nsdhl mutation (Nsdhl(tm1.1Hrm)) to
      investigate the essential role of cholesterol in the early postnatal CNS.
    explanation: >-
      States why this conditional model exists and what it is a model of, which is
      the model-level claim.
  modeled_mechanisms:
  - target: Impaired Hedgehog Signal Transduction
    description: Conditional mutant cerebella show reduced SHH target-gene and Gli1 reporter responses in vivo.
    evidence:
    - reference: PMID:25652406
      reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Using mice that express lacZ under the control of the Gli1 promoter, we were also able to demonstrate variable, but reduced, induction of this SHH response gene in vivo
      explanation: A separate reporter experiment demonstrates reduced SHH response in the conditional mouse CNS.
    relationship: PARTIALLY_RECAPITULATES
    model_scale: TISSUE
    limitations: Bulk tissue and reporter measurements are in a conditional-null mouse CNS, not human CHILD skin or limb tissue. They do not establish that every migration or survival defect is mediated through SHH.
    fidelity: MODERATE
- name: Labrador Retriever NSDHL deletion
  species: Dog
  genotype: Heterozygous deletion removing the last three exons of NSDHL
  publication: PMID:28739597
  description: >-
    A female Labrador Retriever and her crossbred daughter carried a 14,399-base-pair deletion removing the final three NSDHL exons and had a patterned cornification disorder. Their lesions were bilateral and Blaschko-linear, without the typical human limb-reduction phenotype. Two male littermates died at birth but were not genotyped; those deaths cannot establish segregation of a lethal NSDHL genotype.
  genes:
  - preferred_term: NSDHL
    term:
      id: hgnc:13398
      label: NSDHL
  evidence:
  - reference: PMID:28739597
    reference_title: "A Large Deletion in the NSDHL Gene in Labrador Retrievers with a Congenital Cornification Disorder."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Variants in the NSDHL gene cause CHILD syndrome in humans, and the bare
      patches (Bpa) and striated (Str) phenotypes in mice.
    explanation: >-
      The authors situate their canine finding against the human disease and the
      established mouse models, which is what makes this dog a model for CHILD
      syndrome rather than an isolated veterinary case.
  modeled_mechanisms:
  - target: X-Inactivation-Dependent NSDHL Expression Mosaicism
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      An NSDHL deletion in two affected females is associated with Blaschko-linear cutaneous disease, consistent with functional mosaicism.
    limitations: >-
      No allele-expression or enzyme assay directly established the mosaic mechanism, and no longitudinal clone depletion was measured. Bilateral lesions and lack of human-like limb reductions limit phenotype transfer. Male neonatal deaths were ungenotyped.
    readouts:
    - name: Blaschko-linear cutaneous lesion distribution
      target: X-Inactivation-Dependent NSDHL Expression Mosaicism
      direction: ALTERED
      interpretation: >-
        Lesion distribution is compatible with functional X-inactivation mosaicism; it is not a direct allele-expression measurement.
      evidence:
      - reference: PMID:28739597
        reference_title: "A Large Deletion in the NSDHL Gene in Labrador Retrievers with a Congenital Cornification Disorder."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          We investigated a female Labrador Retriever and her crossbred daughter,
          which both showed similar clinical lesions that followed Blaschko's lines.
        explanation: >-
          Reports the lesion distribution behind this readout.
    evidence:
    - reference: PMID:28739597
      reference_title: "A Large Deletion in the NSDHL Gene in Labrador Retrievers with a Congenital Cornification Disorder."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Taken together, our genetic data and the known role of NSDHL in X-linked
        skin disorders strongly suggest that the identified structural variant in
        the NSDHL gene is causative for the phenotype in the two affected dogs.
      explanation: >-
        Supports treating the canine phenotype as an NSDHL-driven model, with the
        authors' own hedged causal language preserved.

    model_scale: TISSUE
experimental_models:
- name: Heterologous expression of NSDHL missense mutants
  experimental_model_type: CELL_LINE
  publication: PMID:40222685
  description: >-
    Heterologous expression assays examined thirteen disease-associated NSDHL missense variants and one deletion. Protein abundance was reduced for all tested variants and partly increased for selected variants at lower temperature or with glycerol. The abstract also implicates heat shock proteins in optimal expression, potentially through protein synthesis. These findings do not distinguish instability from impaired synthesis for every variant or demonstrate restored enzyme activity after abundance rescue.
  evidence:
  - reference: PMID:40222685
    reference_title: "Comprehensive survey of disease-causing missense mutations of the cholesterol synthesis enzyme NSDHL: Low temperature and a chemical chaperone rescue low protein expression of select mutants."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We examined 13 missense mutations and one deletion mutation in the
      cholesterol synthesis enzyme NSDHL (NAD(P) Dependent Steroid
      Dehydrogenase-Like), known to cause the X-linked developmental disorders
      CHILD (congenital hemidysplasia with ichthyosiform erythroderma and limb
      defects) syndrome and CK syndrome.
    explanation: >-
      States that the alleles assayed in this system are the ones that cause CHILD
      syndrome, which is the model-level relevance claim.
  modeled_mechanisms:
  - target: NSDHL Loss of Function
    relationship: MEASURES
    fidelity: MODERATE
    description: >-
      Measures variant-associated reductions in NSDHL protein abundance and partial abundance rescue in selected conditions.
    limitations: >-
      Heterologous overexpression in cultured cells does not report on endogenous
      expression in keratinocytes or on the mosaic tissue context, and a
      temperature or glycerol rescue in culture is not evidence that any
      clinically usable chaperone therapy exists.
    readouts:
    - name: NSDHL mutant protein expression level
      target: NSDHL Loss of Function
      direction: DECREASED
      interpretation: >-
        Steady-state abundance is lower for the tested variants; the assay does not by itself distinguish reduced synthesis from faster degradation.
      evidence:
      - reference: PMID:40222685
        reference_title: "Comprehensive survey of disease-causing missense mutations of the cholesterol synthesis enzyme NSDHL: Low temperature and a chemical chaperone rescue low protein expression of select mutants."
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: >-
          Here we show that protein expression levels were low for all mutants, but
          some could be rescued by a lower temperature (30°C vs. 37°C) and/or the
          chemical chaperone glycerol.
        explanation: >-
          Reports the expression measurement behind this readout.
    evidence:
    - reference: PMID:40222685
      reference_title: 'Comprehensive survey of disease-causing missense mutations of the cholesterol synthesis enzyme NSDHL: Low temperature and a chemical chaperone rescue low protein expression of select mutants.'
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Here we show that protein expression levels were low for all mutants, but some could be rescued by a lower temperature (30°C vs. 37°C) and/or the chemical chaperone glycerol.
      explanation: The measured endpoint is protein abundance; neither catalytic rescue nor clinical benefit follows from it.
    model_scale: MOLECULAR
- name: Paired patient skin keratinocyte and fibroblast cultures
  experimental_model_type: PRIMARY_CELL_CULTURE
  publication: PMID:21753784
  description: >-
    Cultures from affected and clinically unaffected skin of one heterozygous patient were compared by genomic sequencing and RT-PCR. Both genomic alleles were present, while expression differed by site and cell type.
  modeled_mechanisms:
  - target: X-Inactivation-Dependent NSDHL Expression Mosaicism
    description: Patient-derived cultures measure side- and cell-type-specific NSDHL allele expression.
    evidence:
    - reference: PMID:21753784
      reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: 'However, RT-PCR on cDNA from keratinocytes and fibroblasts isolated from the affected versus clinically unaffected side in Patient #1 demonstrated exclusive expression of the mutant allele by affected cultured keratinocytes, while unaffected keratinocytes solely expressed the wild type allele'
      explanation: Cultures from one patient showed side-specific NSDHL allele expression; this is not a longitudinal measure of cell clearance.
    - reference: PMID:21753784
      reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Only the normal allele was expressed by unaffected fibroblasts, but fibroblasts from the clinically affected area expressed an approximately even distribution of normal and mutant alleles.
      explanation: Fibroblast expression in affected skin did not match the exclusively mutant keratinocyte pattern.
    relationship: MEASURES
    model_scale: CELLULAR
    limitations: One patient and selected cultures do not establish the embryonic origin of the midline boundary, the full tissue composition, or a longitudinal selection process.
    fidelity: MODERATE
- name: Conditional-null mouse cerebellar granule-cell precursor cultures
  experimental_model_type: PRIMARY_CELL_CULTURE
  publication: PMID:25652406
  description: >-
    Granule-cell precursors isolated at P4 were cultured for 48 hours with recombinant SHH and cholesterol, LDL, or ketoconazole. Proliferation, Gli1 transcription, viability, morphology, and sterol concentrations were measured separately.
  modeled_mechanisms:
  - target: Impaired Hedgehog Signal Transduction
    description: Cholesterol supplementation largely restores the proliferative response to SHH, while LDL restores Gli1 induction under the tested conditions.
    evidence:
    - reference: PMID:25652406
      reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: We replicated the granule cell precursor proliferation defect in vitro and demonstrate that it results from defective signaling by SHH.
      explanation: The experiment is in cultured mouse granule-cell precursors rather than whole animals or human limb tissue.
    - reference: PMID:25652406
      reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Taken together, these results demonstrate that cholesterol depletion is sufficient to account for virtually all of the reduced response of mutant GCPs to SHH in vitro.
      explanation: Cholesterol supplementation experiments locate a major SHH-response defect in the recipient granule-cell cultures.
    - reference: PMID:25652406
      reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: The addition of cholesterol to the primary GCP cultures led to almost complete restoration of the proliferative response to SHH
      explanation: The culture experiment measures proliferation rescue in response to SHH.
    relationship: PERTURBS
    model_scale: CELLULAR
    limitations: This is a mouse neural culture, not a whole-animal treatment or a human limb/skin experiment. SHH-induced Gli1, proliferation, morphology, and viability are distinct endpoints.
    fidelity: MODERATE
  - target: C4-Methylsterol Accumulation
    description: Upstream inhibition reduces precursor accumulation and improves mutant-cell viability without restoring SHH-induced Gli1 by itself.
    evidence:
    - reference: PMID:25652406
      reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: The concentration of methylsterols was significantly higher in NsdhlΔ5/Y GCPs than Nsdhlflx5/Y GCPs (P < 0.002) in all four culture conditions.
      explanation: Cultured conditional-null mouse granule-cell precursors accumulate methylsterols under the tested conditions.
    - reference: PMID:25652406
      reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Ketoconazole treatment did not affect the viability of WT cells, but it significantly increased mutant cell viability (from 65 to 78%; Fig. 7B).
      explanation: An upstream synthesis inhibitor improved viability in mutant cultures; this supports a precursor-associated injury component but does not identify every accumulated sterol as toxic.
    - reference: PMID:25652406
      reference_title: Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Although the reduction of methylsterol levels by ketoconazole treatment apparently improved the viability and cell morphology of the mutant GCPs, it had no effect on Gli1 expression
      explanation: Cell viability and SHH transcriptional responses were experimentally dissociable; lowering precursors alone did not restore this readout.
    relationship: PERTURBS
    model_scale: CELLULAR
    limitations: Ketoconazole changes multiple sterols. Improved viability does not assign toxicity to every precursor or establish clinical efficacy in CHILD syndrome.
    fidelity: MODERATE
- name: NSDHL-depleted cell models of receptor trafficking
  experimental_model_type: CELL_LINE
  publication: PMID:23125191
  description: >-
    Experimental NSDHL depletion in carcinoma cell systems alters EGFR endosomal handling. Nsdhl-deficient immortalized mouse embryonic fibroblasts separately show accelerated ligand-induced PDGFR loss. These systems probe receptor trafficking rather than reproducing the full CHILD phenotype.
  modeled_mechanisms:
  - target: Increased Receptor Lysosomal Trafficking
    description: NSDHL depletion shifts receptor-associated signals away from recycling endosomes and toward late endosomal compartments.
    evidence:
    - reference: PMID:23125191
      reference_title: Targeting C4-demethylating genes in the cholesterol pathway sensitizes cancer cells to EGF receptor inhibitors via increased EGF receptor degradation.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: In contrast, depletion of either SC4MOL or NSDHL significantly reduced the amount of fluorescently labeled EGFR ... associated with RAB11-positive recycling endosomes after 30 minutes of EGF stimulation.
      explanation: NSDHL knockdown in experimental cells reduced receptor localization to recycling endosomes; this is not a patient-tissue result.
    - reference: PMID:23125191
      reference_title: Targeting C4-demethylating genes in the cholesterol pathway sensitizes cancer cells to EGF receptor inhibitors via increased EGF receptor degradation.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Conversely, SC4MOL and NSDHL-deficient cells showed an accelerated concentration of internalized fluorescently labeled EGF in RAB7-positive ... or EGFR in LAMP1-positive late endosomes
      explanation: Experimental depletion shifts receptor-associated signals toward late endosomal compartments.
    - reference: PMID:23125191
      reference_title: Targeting C4-demethylating genes in the cholesterol pathway sensitizes cancer cells to EGF receptor inhibitors via increased EGF receptor degradation.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Semi-quantitative analysis of PDGFR levels in these fibroblasts treated with PDGF showed accelerated ligand-induced PDGFR loss in NSDHL-deficient Bpa1H cells, but not in controls
      explanation: Mouse embryonic fibroblasts provide a distinct receptor and cellular context supporting altered trafficking.
    relationship: PERTURBS
    model_scale: CELLULAR
    limitations: Cancer-cell knockdown and immortalized mouse fibroblasts differ from patient epidermis; results involving SC4MOL alone are not assigned to NSDHL.
    fidelity: MODERATE
differential_diagnoses:
- name: X-linked chondrodysplasia punctata 2 (Conradi-Hunermann-Happle syndrome)
  disease_term:
    preferred_term: X-linked chondrodysplasia punctata 2
    term:
      id: MONDO:0020603
      label: X-linked chondrodysplasia punctata 2
  description: >-
    EBP-related X-linked chondrodysplasia punctata 2 is a distinct sterol-biosynthesis disorder with overlapping ichthyotic skin and skeletal findings. An early patient described clinically as CHILD syndrome had an EBP nonsense variant and a CDPX2 sterol profile. Current GeneReviews places EBP-related CDPX2 in the differential of NSDHL-related CHILD syndrome; the historical label does not establish EBP as a second causative gene for this entry.
  distinguishing_features:
  - CDPX2 commonly has bilateral asymmetric skin and skeletal involvement. CHILD often has sharper lateralization, but bilateral CHILD presentations mean distribution alone is not definitive.
  - CDPX2 is caused by EBP variants affecting sterol delta8-delta7 isomerization, a different enzymatic step from NSDHL-dependent C4-demethylation.
  - CDPX2 carries a plasma sterol signature of raised 8-dehydrocholesterol and 8(9)-cholestenol that NSDHL-related CHILD syndrome does not
  evidence:
  - reference: PMID:10710235
    reference_title: "Mutations in the NSDHL gene, encoding a 3beta-hydroxysteroid dehydrogenase, cause CHILD syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      EBP was unaffected in the patients analyzed by us demonstrating that CHILD
      syndrome and CDPX2 are not caused by allelic mutations.
    explanation: >-
      Establishes that in this cohort the two are genetically distinct despite
      their shared pathway and overlapping clinical picture.
  - reference: PMID:10710233
    reference_title: "CHILD syndrome caused by deficiency of 3beta-hydroxysteroid-delta8, delta7-isomerase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      although the skeletal defects and skin lesions in CDPX2 are bilateral and
      asymmetric
    explanation: >-
      States the clinical distinction in lesion distribution that separates the
      two on examination.

- name: Inflammatory linear verrucous epidermal nevus (ILVEN)
  disease_term:
    preferred_term: inflammatory linear verrucous epidermal nevus
    term:
      id: MONDO:0019318
      label: inflammatory linear verrucous epidermal nevus
  description: >-
    ILVEN can resemble the inflammatory verrucous CHILD nevus. A reported boy initially suspected to have CHILD syndrome was diagnosed with severe ILVEN despite ipsilateral contracture and short stature. Distribution and extracutaneous findings therefore require interpretation together with molecular and biochemical testing.
  distinguishing_features:
  - A pathogenic NSDHL variant and the corresponding sterol-biosynthesis abnormality support CHILD syndrome; negative or incomplete testing alone does not prove ILVEN.
  - Both ILVEN and CHILD lesions can follow Blaschko lines, so that pattern alone does not distinguish them.
  - ILVEN lacks the ipsilateral skeletal hypoplasia or aplasia of CHILD syndrome, though an ipsilateral limb contracture has been reported in ILVEN, so limb involvement alone does not settle it
  - CHILD syndrome predominantly affects females, but rare mosaic males are reported; male sex alone does not exclude it.
  evidence:
  - reference: PMID:39953436
    reference_title: "Unilateral widespread inflammatory linear verrucous epidermal nevus with ipsilateral limb contracture along the lines of Blaschko: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Initially, we suspected this may be a rare case of CHILD syndrome in a boy.
      However, after further investigation, we confirmed the diagnosis as a
      severe form of ILVEN.
    explanation: >-
      A worked case of the differential actually being made, with CHILD syndrome
      as the initial working diagnosis and ILVEN as the resolution.
  - reference: PMID:39953436
    reference_title: "Unilateral widespread inflammatory linear verrucous epidermal nevus with ipsilateral limb contracture along the lines of Blaschko: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      He also had an associated contracture in the ipsilateral limb and short
      stature.
    explanation: >-
      Documents that the ILVEN case carried ipsilateral limb findings too, which
      is why extracutaneous involvement does not by itself distinguish the two.

- name: CK syndrome
  description: >-
    CK syndrome is an allelic NSDHL disorder associated with hypomorphic variants. Affected males typically have intellectual disability, behavioral problems, infantile seizures, cortical malformations and microcephaly. This differs from the predominant cutaneous and limb phenotype of CHILD syndrome, although both disorders can have CNS manifestations.
  distinguishing_features:
  - CK syndrome typically affects males with hypomorphic NSDHL variants; CHILD syndrome predominantly affects heterozygous females, with rare mosaic males.
  - CK syndrome is dominated by cognitive impairment, seizures, and cortical malformation, whereas intellect is usually normal in CHILD syndrome
  - CK syndrome lacks the lateralized ichthyosiform nevus and ipsilateral limb defects
  evidence:
  - reference: PMID:21290788
    reference_title: "NSDHL-Related Disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The diagnosis of CK syndrome is established in a male proband with a
      hemizygous NSDHL hypomorphic pathogenic variant identified by molecular
      genetic testing that results in partial loss of functional decarboxylating
      sterol-4-alpha-carboxylate 3-dehydrogenase.
    explanation: >-
      States the allelic relationship and the partial-loss-of-function basis that
      separates CK syndrome from CHILD syndrome.

    quote_role: REVIEW_SYNTHESIS
discussions:
- discussion_id: lateralization_mechanism_unknown
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#X-Inactivation-Dependent NSDHL Expression Mosaicism
  prompt: >-
    What mechanism converts random X inactivation into a body-half boundary in
    CHILD syndrome, rather than the finer Blaschko-line mosaicism seen in other
    X-linked genodermatoses?
  rationale: >-
    Expression differences between cultured keratinocytes from affected and unaffected patient skin are consistent with functional mosaicism but do not explain the geometry of the boundary. Age-dependent selection in mouse liver and brain is a separate observation; human skin clone clearance has not been measured longitudinally. Mouse and canine lesion patterns differ from typical human lateralization. Paired spatial and allele-expression measurements could distinguish developmental lineage allocation from subsequent tissue-specific selection.
  proposed_experiments:
  - experiment_id: lateralization_lineage_mapping
    name: Lineage and allele-expression mapping across the midline in CHILD skin
    description: >-
      Single-cell or spatial transcriptomic mapping of NSDHL allele expression
      across the midline boundary in affected individuals, paired with clonal
      lineage inference, to determine whether the boundary reflects an early
      embryonic left-right lineage restriction, a later selective clearance front,
      or an unrecognized signalling boundary.
  evidence:
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: 'However, RT-PCR on cDNA from keratinocytes and fibroblasts isolated from the affected versus clinically unaffected side in Patient #1 demonstrated exclusive expression of the mutant allele by affected cultured keratinocytes, while unaffected keratinocytes solely expressed the wild type allele'
    explanation: Cultures from one patient showed side-specific NSDHL allele expression; this is not a longitudinal measure of cell clearance.
  - reference: PMID:21753784
    reference_title: Pathogenesis-based therapy reverses cutaneous abnormalities in an inherited disorder of distal cholesterol metabolism.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Only the normal allele was expressed by unaffected fibroblasts, but fibroblasts from the clinically affected area expressed an approximately even distribution of normal and mutant alleles.
    explanation: Fibroblast expression in affected skin did not match the exclusively mutant keratinocyte pattern.
  - reference: PMID:19631568
    reference_title: Developmental expression pattern of the cholesterogenic enzyme NSDHL and negative selection of NSDHL-deficient cells in the heterozygous Bpa(1H)/+ mouse.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: These data suggest that the higher percentage of WT hepatocytes present in livers from older Bpa1H females is the cumulative result of postnatal differences in either the growth rate or survival of WT vs mutant hepatocytes.
    explanation: Cross-sectional age groups support selection in mouse liver while leaving differential survival versus proliferation unresolved.
- discussion_id: male_lethality_placental_mechanism_human
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Placental Labyrinth Dysmorphogenesis
  prompt: >-
    Do the placental abnormalities associated with prenatal death in Nsdhl-mutant mice contribute to human male lethality?
  rationale: >-
    Nsdhl mouse studies associate placental labyrinth abnormalities with prenatal death, but the timing varies by allele and the findings do not establish a universal human mechanism. Rodent and human placental X-inactivation differ. A report of recurrent male pregnancy losses identified maternal and fetal NSDHL c.790-6C>T, but classified it as a variant of uncertain significance, predicted a splice effect without functional confirmation, and tested only one lost conceptus. That report does not confirm NSDHL-mediated recurrent fetal lethality or the placental mechanism in humans.
  proposed_experiments:
  - experiment_id: human_nsdhl_trophoblast_model
    name: NSDHL-null human trophoblast organoid vascularization assay
    description: >-
      Generate NSDHL loss-of-function human trophoblast stem cell or placental
      organoid models and assay Hedgehog pathway activity, trophoblast
      proliferation, and vascular network formation, to test whether the murine
      labyrinth phenotype has a human counterpart independent of rodent-specific
      placental X inactivation.
  evidence:
  - reference: PMID:15639195
    reference_title: "Placental defects are associated with male lethality in bare patches and striated embryos deficient in the NAD(P)H Steroid Dehydrogenase-like (NSDHL) Enzyme."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      X-inactivation is non-random in females in most lineages of the rodent
      placenta with preferential inactivation of the paternal X chromosome.
    explanation: >-
      States the rodent-specific placental X-inactivation arrangement that the
      mouse inference depends on and that does not transfer to humans.
  - reference: PMID:36504312
    reference_title: 'Etiological identification of recurrent male fatality due to a novel NSDHL gene mutation using trio whole-exome sequencing: A rare case report and literature review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: According to ACMG guidelines, the variant has been classified as a variant of uncertain significance.
    explanation: The primary report explicitly classifies c.790-6C>T as uncertain; its more assertive abstract does not establish causality.
  - reference: PMID:36504312
    reference_title: 'Etiological identification of recurrent male fatality due to a novel NSDHL gene mutation using trio whole-exome sequencing: A rare case report and literature review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: However, further work is required to verify the relationship between the c.790-6C>T variant and CHILD syndrome.
    explanation: The authors acknowledge that the variant-disease relationship requires further verification.
- discussion_id: nsdhl_versus_ebp_nosological_boundary
  kind: INTERPRETATION
  status: OPEN
  attaches_to:
  - genetic#NSDHL
  prompt: >-
    How should the historical EBP-positive case labeled CHILD syndrome be interpreted within the current NSDHL-defined disease boundary?
  rationale: >-
    An early report identified an EBP nonsense variant and a CDPX2 plasma sterol profile in a patient clinically labeled CHILD syndrome. The NSDHL discovery cohort instead found EBP unaffected, and current GeneReviews defines CHILD syndrome through NSDHL while listing EBP-related CDPX2 as a differential diagnosis. The early clinical label alone is insufficient evidence of locus heterogeneity. Reassessment of historical cases may clarify phenotypic overlap, but does not justify recording EBP as causative for NSDHL-related CHILD syndrome.
  proposed_experiments:
  - experiment_id: child_locus_reassessment_cohort
    name: Genotype and sterol reassessment of the assembled CHILD case literature
    description: >-
      Assemble the published CHILD syndrome cases with molecular data, and where
      material allows, determine NSDHL versus EBP genotype together with plasma
      sterol profile and lesion distribution, to establish whether EBP-related
      cases form a clinically separable subgroup or are distributed through the
      CHILD phenotype.
  evidence:
  - reference: PMID:10710233
    reference_title: "CHILD syndrome caused by deficiency of 3beta-hydroxysteroid-delta8, delta7-isomerase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We speculate that at least some cases of CHILD syndrome are allelic with
      CDPX2 caused by 3beta-hydroxysteroid-delta8,delta7-isomerase deficiency.
    explanation: >-
      The authors' own hedged phrasing is the open question this discussion
      records.

notes: >-
  This entry covers NSDHL-related CHILD syndrome. CK syndrome is an allelic differential diagnosis, and EBP-related CDPX2 is a distinct sterol-biosynthesis disorder. Intellect is usually normal, although brain malformations and neurologic manifestations can occur. Sterol-dependent Hedgehog effects are supported principally by experimental models and should not be interpreted as a primary ciliary assembly defect. Tissue-specific mosaicism limits the interpretation of blood testing and systemic biochemical measurements.

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