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Classifications

Harrison's Part

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Inheritance

1

Autosomal dominant HP:0000006

Heterozygous GLI2 loss-of-function alleles segregate in an autosomal dominant pattern, but penetrance is strikingly incomplete: pathogenic variants are frequently transmitted by an asymptomatic parent, or by a parent whose only manifestation is postaxial polydactyly. A substantial minority of probands carry a de novo variant.

Autosomal dominant inheritance Penetrance: INCOMPLETE Expressivity: VARIABLE

Show evidence (4 references)

PMID:25878059 SUPPORT Human Clinical

"The inheritance pattern was autosomal dominant with incomplete penetrance and variable expressivity. The mutation was frequently inherited from an asymptomatic parent."

A review of 25 patients in 16 families with heterozygous truncating GLI2 mutations establishes autosomal dominant inheritance with incomplete penetrance and frequent transmission from an unaffected carrier parent.

PMID:34921505 SUPPORT Human Clinical

"Substantial phenotypic variability and nonpenetrance have been described, posing difficulties in the counseling of affected families."

Confirms non-penetrance and phenotypic variability as the central counselling problem in GLI2-related disease.

PMID:33235745 SUPPORT Human Clinical

"This case series and review of the literature support that patients with pathogenic variants of the GLI2 gene demonstrate an autosomal dominant inheritance pattern, variable expressivity, and incomplete penetrance."

A three-generation family with a shared GLI2 deletion directly demonstrates the dominant inheritance, variable expressivity and incomplete penetrance.

+ 1 more reference

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Subtypes

2

Pituitary anomaly with postaxial polydactyly (Culler-Jones spectrum) MONDO:0014369

The predominant presentation of GLI2 loss of function: hypopituitarism (isolated GH deficiency through panhypopituitarism) with a hypoplastic anterior pituitary and ectopic posterior pituitary lobe, postaxial polydactyly, and subtle midfacial features, in the absence of any forebrain cleavage defect. Catalogued in its own right as Culler-Jones syndrome (OMIM 615849, MONDO:0014369, Orphanet 420584), which is grounded here as this subtype's subtype_term rather than split into a separate dismech entry - see the hpe9_nomenclature discussion for that decision.

Show evidence (2 references)

PMID:24744436 SUPPORT Human Clinical

"Individuals with truncating mutations in GLI2 typically present with pituitary anomalies, polydactyly and subtle facial features rather than HPE."

Defines the dominant, non-HPE presentation of GLI2 truncating variants.

PMID:20685856 SUPPORT Human Clinical

"Magnetic resonance imaging of four patients with GLI2 mutations and hypopituitarism showed a hypoplastic anterior pituitary and an ectopic posterior pituitary lobe without HPE."

Establishes the characteristic pituitary imaging phenotype occurring without holoprosencephaly.

GLI2-related holoprosencephaly (forebrain non-cleavage)

The minority presentation in which GLI2 loss of function produces frank holoprosencephaly, most often semilobar, with the classic HPE facial features. Reported in roughly 6% of individuals with pathogenic GLI2 variants and in only 1 of 43 carriers of truncating variants in an earlier series. No subtype_term is given because this tier has no MONDO class distinct from the entry's own disease_term: "GLI2-related disease with forebrain non-cleavage" simply is holoprosencephaly 9 (MONDO:0012563). Only the mild tier acquired a separate identifier, because it was historically split out as Culler-Jones syndrome.

Show evidence (2 references)

PMID:24744436 SUPPORT Human Clinical

"only 1 of 43 had frank HPE"

Quantifies how uncommon frank holoprosencephaly is among carriers of truncating GLI2 variants.

PMID:21204792 SUPPORT Human Clinical

"Here we described six Brazilian patients with phenotypic manifestations that range from isolated cleft lip/palate with polydactyly, branchial arch anomalies to semi-lobar holoprosencephaly."

Documents the severe end of the spectrum (semilobar HPE) within a GLI2 mutation-positive series.

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Mechanistic Hypotheses

3

Simple haploinsufficiency of the GLI2 activator

gli2_haploinsufficiency CANONICAL

Evidence balance 2 support

The dominant model: pathogenic alleles are functionally null, the wild-type allele is unaffected, and disease results from a halved dose of GLI2 activator. Supported by the absence of dominant-negative activity in the original functional assays and by the fact that whole-gene deletions reproduce the phenotype.

Show evidence (2 references)

PMID:14581620 SUPPORT In Vitro

"None of the mutant alleles manifested dominant negative activity in these studies."

No dominant-negative activity was demonstrable for any patient allele, favouring haploinsufficiency.

PMID:22106008 SUPPORT Human Clinical

"Our findings confirm the association of haploinsufficiency of GLI2 and mild HPE spectrum features."

Whole-gene deletion phenocopies intragenic truncating variants, the classic argument for haploinsufficiency.

Allele-specific dominant-negative interference by truncated GLI2

gli2_dominant_negative ALTERNATIVE

Evidence balance 1 support

An alternative, probably allele-restricted mechanism in which a truncated GLI2 protein retaining the N-terminal repressor domain actively interferes with Hedgehog signalling rather than simply being inert. Reported for the C-terminal frameshift p.P1167LfsX52 in a Culler-Jones family, but not demonstrated for the alleles tested in the founding functional study.

Show evidence (1 reference)

PMID:30629636 SUPPORT In Vitro

"Functional assays confirmed the pathogenicity of the identified variant and revealed a dominant-negative effect of mutant GLI2 on Hedgehog signalling."

Cell-based assays show a dominant-negative effect for this specific truncating allele.

Gene-environment second hit determines penetrance

gli2_second_hit EMERGING

Evidence balance 2 support

Penetrance and severity are set not by the GLI2 allele alone but by whether a second genetic or environmental insult perturbs the already dose-limited Hedgehog pathway during the first-trimester patterning window. Strong support in the mouse; in humans the specific modifiers remain unidentified, and a possible digenic GLI2/HESX1 family has been reported.

Show evidence (2 references)

PMID:27585885 SUPPORT Model Organism

"Here, we demonstrate that mutations in Gli2, which encodes a Hedgehog pathway transcription factor, can cause or predispose to HPE depending upon gene dosage."

Frames Gli2 lesions as either causal or predisposing depending on dosage and additional exposure.

PMID:39938560 SUPPORT Human Clinical

"A possible digenic origin (GLI2/HESX1) is proposed in one family."

A single reported family suggests a human second-locus contribution; marked PARTIAL because it is a proposal in one family, not established digenic inheritance.

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Discussions and Knowledge Gaps

3

Is "holoprosencephaly 9" the right name for a disorder in which frank holoprosencephaly occurs in roughly 6% of carriers?

CONTROVERSY OPEN hpe9_nomenclature

Attached to

pathophysiology#Holoprosencephaly-Spectrum Forebrain and Midfacial Malformation

The HPE9 designation predates the large genotype-phenotype series and reflects the ascertainment of the original cohorts, which were screened for holoprosencephaly. Subsequent series consistently show that pituitary anomalies and postaxial polydactyly, not forebrain non-cleavage, are the modal presentation, which is why the milder presentation was split out as Culler-Jones syndrome. dismech keeps a single entry under the MONDO label holoprosencephaly 9 with the two presentations modelled as subtypes, but the naming remains a live question and a curator considering a separate Culler-Jones entry should read this note first.

Show evidence (1 reference)

PMID:24744436 SUPPORT Human Clinical

"Individuals with truncating mutations in GLI2 typically present with pituitary anomalies, polydactyly and subtle facial features rather than HPE."

The finding that motivates the nomenclature question.

What determines whether a human GLI2 loss-of-function carrier is unaffected, has isolated polydactyly, or has hypopituitarism with holoprosencephaly?

KNOWLEDGE GAP OPEN gli2_penetrance_modifiers

Attached to

pathophysiology#Reduced Developmental Buffering of the Hedgehog Pathway

The mouse work establishes that a second hit converts silent Gli2 heterozygosity into overt disease, but the human modifiers are unknown. No modifier locus has been validated, only a single family with a proposed digenic GLI2/HESX1 contribution, and no human study has tested the teratogen interaction directly. Identifying the modifiers would convert an unpredictable counselling situation into a stratifiable one.

Proposed experiments

Modifier sequencing in phenotypically discordant carrier relatives

exp_gli2_modifier_sequencing_discordant_relatives

Sequence the full Hedgehog pathway and known congenital hypopituitarism genes in relatives who share an identical GLI2 allele but differ in phenotype, to test for modifier or second-locus alleles. Enrichment of pathway alleles in affected relative to unaffected carriers would support an oligogenic contribution to penetrance; no enrichment would point instead to stochastic or environmental determinants.

Prospective periconceptional exposure cohort of GLI2 carriers

exp_gli2_prospective_periconceptional_exposure_cohort

Assemble a cohort of pregnancies in known GLI2 carrier families with prospectively recorded periconceptional exposures (alcohol, maternal diabetes, cholesterol biosynthesis inhibitors) and relate exposure to offspring phenotype. An exposure-severity gradient would translate the mouse gene-environment model into humans; phenotype independent of recorded exposures would confine that model to the mouse.

Hedgehog dose-response assay in patient fibroblasts

exp_gli2_hedgehog_dose_response_patient_fibroblasts

Measure Hedgehog ligand dose-response in fibroblasts from GLI2 variant carriers spanning the phenotypic range, mirroring the mouse cellular assay. Residual pathway output correlating with phenotype severity would make cellular Hedgehog responsiveness a candidate predictive biomarker; uniform attenuation across phenotypically discordant carriers would exclude it.

Show evidence (1 reference)

PMID:39938560 SUPPORT Human Clinical

"A possible digenic origin (GLI2/HESX1) is proposed in one family."

The only human second-locus lead currently reported; marked PARTIAL because it is a single proposed family.

Does the mouse Gli2 heterozygote faithfully model the human GLI2 carrier, given that heterozygous mice are phenotypically normal whereas a majority of human carriers manifest at least polydactyly?

HUMAN MODEL MISMATCH OPEN gli2_mouse_heterozygote_mismatch

Attached to

pathophysiology#Reduced Developmental Buffering of the Hedgehog Pathway

The human disorder is dominant with roughly 65% of pathogenic-variant carriers showing postaxial polydactyly, whereas Gli2 heterozygous mice are described as indistinguishable from wild-type littermates without a second insult, and the murine phenotype that does resemble severe human holoprosencephaly requires homozygous loss on a permissive background. The species therefore differ in where the developmental threshold sits relative to a single functional allele. This matters because the second-hit model of human non-penetrance rests largely on heterozygous-mouse data; if the human heterozygote is already below threshold in the limb, the environmental component may be less necessary for the human phenotype than the mouse experiments imply.

Proposed experiments

Systematic limb phenotyping of Gli2 heterozygous mice across backgrounds

exp_gli2_het_mouse_limb_phenotyping_across_backgrounds

Score autopod morphology in Gli2 heterozygous mice on several genetic backgrounds, since polydactyly may have been under-ascertained in models scored primarily for craniofacial dysmorphology. Finding unreported polydactyly would reconcile the species; confirmed absence across backgrounds would establish a real species difference in developmental threshold.

Cross-species Hedgehog dose-response comparison

exp_gli2_cross_species_hedgehog_dose_response

Compare Hedgehog ligand dose-response curves in mouse Gli2 heterozygous fibroblasts and human GLI2-variant patient fibroblasts. Lower residual pathway output in human cells would explain why human heterozygotes manifest and mouse heterozygotes do not; equivalent curves would locate the difference downstream of cellular Hedgehog responsiveness.

Show evidence (2 references)

PMID:27585885 SUPPORT Model Organism

"Although normally indistinguishable from wild-type littermates, we demonstrate that mice with single-allele Gli2 mutations exhibit increased penetrance and severity of HPE in response to low-dose teratogen exposure."

States the mouse heterozygote baseline that differs from the human carrier state.

PMID:34921505 SUPPORT Human Clinical

"The most prevalent phenotypic feature is post-axial polydactyly (65%)"

Establishes that most human heterozygotes are not phenotypically silent, unlike the mouse.

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Pathophysiology

11

GLI2 Loss-of-Function Variant

A heterozygous truncating variant, pathogenic zinc-finger missense variant, or whole-gene 2q14.2 deletion removes or inactivates one GLI2 allele. Truncating alleles delete the C-terminal transcriptional activation domain, so the residual protein cannot drive Hedgehog target-gene transcription.

DNA-binding transcription factor activity GO:0003700 ↓ DECREASED

Downstream

Reduced GLI2 Transcriptional Activator Dose

Show evidence (2 references)

PMID:20685856 SUPPORT Human Clinical

"All predict a truncated protein with loss of the C-terminal activator domain."

Identifies loss of the C-terminal activator domain as the shared molecular consequence of the pathogenic truncating alleles.

PMID:14581620 SUPPORT In Vitro

"We also demonstrate that these mutations lack GLI2 activity."

Frog-embryo and C3H10T1/2 osteogenic-induction assays show the patient alleles have no GLI2 activity, confirming loss of function.

Reduced GLI2 Transcriptional Activator Dose

GLI2 is the principal activator among the three vertebrate GLI transcription factors that transduce the Hedgehog signal. With one allele inactivated, the dose of full-length GLI2 activator available for nuclear translocation and target-gene activation falls. The mutant alleles show no dominant-negative activity in the original functional assays, so the mechanism is haploinsufficiency rather than poisoning of the wild-type product - although a later C-terminal frameshift allele did display a dominant-negative effect, leaving room for allele-specific mechanisms.

DNA-binding transcription factor activity GO:0003700 ↓ DECREASED

Downstream

Attenuated Hedgehog Transcriptional Output

Show evidence (3 references)

PMID:14581620 SUPPORT Other

"Gli2 is one of three vertebrate transcription factors implicated as obligatory mediators of Shh signal transduction."

Places GLI2 as an obligatory transducer of the Hedgehog signal, the step that is dose-reduced here.

PMID:14581620 SUPPORT In Vitro

"None of the mutant alleles manifested dominant negative activity in these studies."

Co-injection experiments with wild-type GLI2 found no dominant-negative activity, supporting simple haploinsufficiency.

PMID:30629636 SUPPORT In Vitro

"Functional assays confirmed the pathogenicity of the identified variant and revealed a dominant-negative effect of mutant GLI2 on Hedgehog signalling."

A C-terminal frameshift allele (p.P1167LfsX52) behaved as a dominant negative in cell-based assays, so haploinsufficiency may not be the mechanism for every pathogenic allele. Marked PARTIAL because it qualifies rather than supports the haploinsufficiency model.

Attenuated Hedgehog Transcriptional Output

Reduced GLI2 activator dose lowers transcriptional output of the Hedgehog pathway in responding cells. Mouse work shows this is not an all-or-nothing switch: Gli2 heterozygosity produces a dosage-dependent attenuation of Hedgehog ligand responsiveness at the cellular level, which is compatible with normal development at baseline but leaves the pathway with less reserve.

neural progenitor cell CL:0011020

smoothened signaling pathway GO:0007224 ↓ DECREASED

primary cilium GO:0005929

Downstream

Impaired Ventral Forebrain Midline Patterning

Defective Rathke Pouch and Anterior Pituitary Organogenesis

Disrupted Anteroposterior Limb Bud Patterning

Disrupted First Branchial Arch and Craniofacial Patterning

Reduced Developmental Buffering of the Hedgehog Pathway

Show evidence (2 references)

PMID:27585885 SUPPORT Model Organism

"This genetic predisposition is associated with a Gli2 dosage-dependent attenuation of Hedgehog ligand responsiveness at the cellular level."

Directly demonstrates that Gli2 gene dosage sets the magnitude of cellular Hedgehog responsiveness, the central effector step of this disease.

PMID:22967285 SUPPORT Other

"GLI2 is a downstream transcription factor in Sonic Hedgehog signalling, acting early in ventral forebrain and pituitary development."

Locates GLI2 in the Hedgehog cascade and names the two tissues whose development is most dependent on it.

Impaired Ventral Forebrain Midline Patterning

Hedgehog signalling from the prechordal plate ventralizes the rostral neuroepithelium and drives the midline separation of the eye field and prosencephalon. Reduced GLI2-dependent output impairs this midline induction. In the mouse, complete Gli2 loss abolishes the floor plate and, on a permissive genetic background, reproduces the medial forebrain deficiency and midfacial hypoplasia of severe human holoprosencephaly; in humans the heterozygous state usually leaves cleavage intact and manifests only as midfacial hypoplasia and hypotelorism.

neurecto-epithelial cell CL:0000710

telencephalon regionalization GO:0021978 ⚠ ABNORMAL floor plate formation GO:0021508 ↓ DECREASED

Downstream

Holoprosencephaly-Spectrum Forebrain and Midfacial Malformation

Show evidence (3 references)

PMID:14581620 SUPPORT Other

"The secreted protein Shh acts as a crucial factor that patterns the ventral forebrain and is required for the division of the primordial eye field and brain into two discrete halves."

States the developmental process that GLI2-dependent Hedgehog output serves in the ventral forebrain.

PMID:9655799 SUPPORT Model Organism

"We have found that the floor plate throughout the midbrain, hindbrain and spinal cord does not form in Gli2 homozygotes."

Mouse null data show Gli2 is required for ventral midline (floor plate) induction, the CNS-patterning step disrupted in this node.

PMID:27585885 SUPPORT Model Organism

"On the C57BL/6J background, homozygous GLI2 loss of function results in the characteristic brain and facial features seen in severe human HPE, including midfacial hypoplasia, hypotelorism and medial forebrain deficiency with loss of ventral neurospecification."

Shows that complete Gli2 loss reproduces the human midline forebrain and face phenotype, linking this node to its clinical consequence.

Defective Rathke Pouch and Anterior Pituitary Organogenesis

Hedgehog signalling is required at an early step of pituitary formation, when Rathke pouch is induced from the oral ectoderm beneath the ventral diencephalon. Reduced GLI2 activator output impairs anterior pituitary specification and growth and disturbs the descent/positioning of the posterior lobe, producing anterior pituitary hypoplasia with an ectopic posterior pituitary and interrupted stalk. Gli2 mutant mice have hypoplastic anterior and absent posterior pituitary glands, and in zebrafish loss of Gli-mediated signalling causes the adenohypophyseal anlage to transdifferentiate into lens.

somatotroph CL:0002312

pituitary gland development GO:0021983 ⚠ ABNORMAL

Downstream

Combined Pituitary Hormone Deficiency

Show evidence (4 references)

PMID:14581620 SUPPORT Other

"Our data support a growing body of evidence that Shh signaling is necessary for an early step in pituitary formation"

Places the GLI2-dependent requirement at an early step of pituitary organogenesis.

PMID:25878059 SUPPORT Model Organism

"Gli2 mutant mice have hypoplastic anterior and absent posterior pituitary glands."

Mouse data directly demonstrate that Gli2 loss disrupts development of both pituitary lobes.

PMID:10960781 SUPPORT Model Organism

"The observation argues that overall inhibition of Shh-Gli signaling leads the adenohypophysis anlage to transdifferentiate into lens."

Zebrafish gli2 (you-too) mutants show that Shh-Gli signalling maintains adenohypophyseal identity; its loss redirects the pituitary primordium to a lens fate.

+ 1 more reference

Disrupted Anteroposterior Limb Bud Patterning

Hedgehog signalling from the zone of polarizing activity, read out through the GLI transcription factors, specifies digit number and identity along the anteroposterior axis of the limb bud. Reduced GLI2 activator dose perturbs this readout and produces an extra postaxial digit. This is the most prevalent manifestation of a pathogenic GLI2 variant and the mildest expression of the condition - frequently the only finding in a transmitting parent.

limb morphogenesis GO:0035108 ⚠ ABNORMAL smoothened signaling pathway GO:0007224 ↓ DECREASED

Downstream

Postaxial Polydactyly

Show evidence (2 references)

PMID:34921505 SUPPORT Human Clinical

"The most prevalent phenotypic feature is post-axial polydactyly (65%) which is also the mildest phenotypic expression of the condition, reported in many parents of individuals with systemic findings."

Establishes postaxial polydactyly as the most frequent and mildest expression of a pathogenic GLI2 variant.

PMID:31782289 SUPPORT Human Clinical

"His father and a six-year-old brother with the identical mutation also had unilateral postaxial polydactyly and mid-facial hypoplasia although there was no pituitary hormone deficiency."

Shows postaxial polydactyly occurring as the isolated manifestation in relatives carrying the identical GLI2 splice variant.

Disrupted First Branchial Arch and Craniofacial Patterning

Beyond the midline, reduced Hedgehog output perturbs patterning of the first branchial arch and its derivatives and of the developing palate and orbit, producing midface hypoplasia, orofacial clefting, temporomandibular joint anomalies, and - at the severe end - orbital anomalies with anophthalmia or microphthalmia and heminasal aplasia.

roof of mouth development GO:0060021 ⚠ ABNORMAL

Downstream

Holoprosencephaly-Spectrum Forebrain and Midfacial Malformation

Show evidence (2 references)

PMID:21204792 SUPPORT Human Clinical

"Subsequently, anophthalmia plus orbital anomalies, heminasal aplasia, branchial arch anomalies and polydactyly have also been incorporated into the general phenotype."

Documents branchial arch and orbital anomalies as part of the GLI2 phenotype.

PMID:21204792 SUPPORT Human Clinical

"Novel sequence variants were found in the GLI2 gene in patients with marked involvement of the temporomandibular joint (TMJ), a new clinical finding observed with mutations of this gene."

Adds temporomandibular joint involvement, a first-arch derivative, to the craniofacial arm of the phenotype.

Reduced Developmental Buffering of the Hedgehog Pathway

A single functional GLI2 allele is usually sufficient for normal development, which is why so many carriers are unaffected. What haploinsufficiency removes is reserve: the pathway becomes dose-limited and therefore vulnerable to a second genetic or environmental hit during the first-trimester patterning window. Mice heterozygous for a Gli2 null allele are indistinguishable from wild-type littermates at baseline but show markedly increased penetrance and severity of holoprosencephaly after low-dose teratogen or ethanol exposure. This provides the mechanistic account of the incomplete penetrance that defines the human disorder, but the specific human second hits remain unidentified.

Downstream

Holoprosencephaly-Spectrum Forebrain and Midfacial Malformation

Show evidence (3 references)

PMID:27585885 SUPPORT Model Organism

"Although normally indistinguishable from wild-type littermates, we demonstrate that mice with single-allele Gli2 mutations exhibit increased penetrance and severity of HPE in response to low-dose teratogen exposure."

The defining gene-environment experiment: Gli2 heterozygosity is silent alone but converts a subthreshold teratogen exposure into holoprosencephaly.

PMID:24586787 SUPPORT Model Organism

"While Shh(+/-) and Gli2(+/-) mice have been described as phenotypically normal, these results illustrate a functional haploinsufficiency of both genes in combination with ethanol exposure."

Independent replication with prenatal ethanol as the second hit, supporting the reduced-buffering model.

PMID:22106008 SUPPORT Human Clinical

"Consistent with prior reports, we observed incomplete penetrance of the deletion in the family, illustrating the multifactorial etiology of holoprosencephaly spectrum features."

Human family data showing the same incomplete penetrance the mouse model explains.

Combined Pituitary Hormone Deficiency

Structural anterior pituitary failure translates into deficiency of one or more anterior pituitary hormones - most often growth hormone, frequently combined with TSH, ACTH, prolactin and gonadotropin deficiency, and occasionally with antidiuretic hormone deficiency (diabetes insipidus) when the posterior lobe axis is involved. Clinically this presents as neonatal hypoglycaemia and cholestasis, micropenis and cryptorchidism in male infants, and growth failure in childhood.

growth hormone secretion GO:0030252 ↓ DECREASED

Show evidence (2 references)

PMID:20685856 SUPPORT Human Clinical

"The index case of family 1 had polydactyly, hypoglycemia, and seizures, and GH, TSH, prolactin, ACTH, LH, and FSH deficiencies."

Illustrates the multi-axis anterior pituitary hormone deficiency produced by a truncating GLI2 variant.

PMID:39938560 SUPPORT Human Clinical

"Most patients with a GLI2 variant (21/23, 91%) had hypopituitarism, including 21.7% (5/23) presenting isolated growth hormone deficiency."

Quantifies the hormonal phenotype in the largest cohort of pathogenic GLI2 variants, including the isolated-GH-deficiency subset.

Holoprosencephaly-Spectrum Forebrain and Midfacial Malformation

The structural end-point of impaired midline patterning: most commonly subtle midface hypoplasia, hypotelorism, orofacial clefting and a solitary median maxillary central incisor, and less commonly overt lobar or semilobar holoprosencephaly. The severity of the brain malformation is the dominant determinant of neurodevelopmental outcome.

Show evidence (2 references)

PMID:24744436 SUPPORT Human Clinical

"A common facial phenotype was seen in individuals (with midface hypoplasia, cleft lip/palate and hypotelorism) with truncating mutations."

Defines the recurrent midline facial gestalt of GLI2 truncating variants.

PMID:34921505 SUPPORT Human Clinical

"HPE (6%) or other brain structure abnormalities (15%)"

Quantifies how much of the GLI2 morbidity spectrum is structural brain malformation.

Postaxial Polydactyly

An extra digit on the ulnar or fibular side of the hand or foot, unilateral or bilateral. It is the single most frequent finding in GLI2 variant carriers and is often the only clue that an apparently unaffected parent is a carrier.

Show evidence (1 reference)

PMID:34921505 SUPPORT Human Clinical

"The most prevalent phenotypic feature is post-axial polydactyly (65%)"

Postaxial polydactyly is the most prevalent manifestation across 60 individuals with pathogenic GLI2 variants.

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Pathograph

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

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Phenotypes

25

Digestive 1

Neonatal cholestasis HP:0001396

Show evidence (1 reference)

PMID:31782289 SUPPORT Human Clinical

"developed cholestasis and hypoglycaemia in the neonatal period"

Case-level documentation of neonatal cholestasis in GLI2-related hypopituitarism.

Endocrine 3

Growth hormone deficiency FREQUENT Secondary growth hormone deficiency HP:0008240

Show evidence (1 reference)

PMID:25878059 SUPPORT Human Clinical

"Twenty-five patients (16 families) had heterozygous truncating mutations, and the phenotype frequently included GH deficiency, a small anterior pituitary lobe and an ectopic/undescended posterior pituitary lobe on magnetic resonance imaging and postaxial polydactyly."

GH deficiency is described as a frequent component of the truncating-variant phenotype across 25 patients in 16 families.

Diabetes insipidus OCCASIONAL HP:0000873

Show evidence (2 references)

PMID:20685856 SUPPORT Human Clinical

"These phenotypes support partial penetrance, variable polydactyly, midline facial defects, and pituitary hormone deficiencies, including diabetes insipidus, conferred by heterozygous frameshift or nonsense GLI2 mutations."

Diabetes insipidus is explicitly included in the hormone-deficiency spectrum of truncating GLI2 variants.

PMID:22967285 SUPPORT Human Clinical

"Two patients had additional diabetes insipidus, indicating deficiencies of anterior and posterior pituitary lobes."

Two of the 24 GLI2-variant patients in this cohort had diabetes insipidus (about 8%), which maps to OCCASIONAL (5-29%).

Hypogonadotropic hypogonadism HP:0000044

Show evidence (1 reference)

PMID:20685856 SUPPORT Human Clinical

"one cousin with GH, TSH, LH, and FSH deficiencies"

Gonadotropin deficiency is documented within a GLI2 mutation-positive family.

Eye 1

Hypotelorism HP:0000601

Show evidence (1 reference)

PMID:24744436 SUPPORT Human Clinical

"with midface hypoplasia, cleft lip/palate and hypotelorism"

Hypotelorism is listed as a component of the recurrent GLI2 facial phenotype.

Genitourinary 2

Micropenis HP:0000054

Show evidence (1 reference)

PMID:31782289 SUPPORT Human Clinical

"high palatal arch, micropenis, and bilateral cryptorchidism"

Documents micropenis in a GLI2 multiple-pituitary-hormone-deficiency index case.

Cryptorchidism HP:0000028

Show evidence (1 reference)

PMID:20685856 SUPPORT Human Clinical

"In family 2, a boy had cryptorchidism, cleft lip and palate, and GH deficiency."

Documents cryptorchidism co-occurring with clefting and GH deficiency in a GLI2 family.

Head and Neck 3

Midface hypoplasia FREQUENT Midface retrusion HP:0011800

Show evidence (2 references)

PMID:24744436 SUPPORT Human Clinical

"A common facial phenotype was seen in individuals (with midface hypoplasia, cleft lip/palate and hypotelorism) with truncating mutations."

Midface hypoplasia is part of the common facial phenotype of truncating GLI2 variants.

PMID:34921505 SUPPORT Human Clinical

"dysmorphic facial features (35%)"

Dysmorphic facial features in 35% of 60 individuals with pathogenic GLI2 variants maps to FREQUENT (30-79%).

Orofacial clefting OCCASIONAL HP:0000202

Show evidence (2 references)

PMID:34921505 SUPPORT Human Clinical

"orofacial clefting (17%)"

Orofacial clefting in 17% of 60 individuals with pathogenic GLI2 variants maps to OCCASIONAL (5-29%).

PMID:22106008 SUPPORT Human Clinical

"bilateral cleft lip and palate and abnormal pituitary gland formation with panhypopituitarism"

Case-level documentation of bilateral cleft lip and palate with panhypopituitarism in a GLI2 deletion carrier.

Solitary median maxillary central incisor HP:0006315

Show evidence (1 reference)

PMID:34921505 SUPPORT Human Clinical

"a solitary median maxillary central incisor is part of the GLI2-related phenotypic variability"

Establishes SMMCI within the GLI2 phenotype. No frequency is recorded because the source reports no proportion - it adds the finding to the spectrum on the basis of isolated observations.

Limbs 1

Postaxial polydactyly FREQUENT HP:0100259

Show evidence (2 references)

PMID:34921505 SUPPORT Human Clinical

"The most prevalent phenotypic feature is post-axial polydactyly (65%) which is also the mildest phenotypic expression of the condition"

65% of 60 individuals with pathogenic GLI2 variants maps to FREQUENT (30-79%).

PMID:31782289 SUPPORT Human Clinical

"He had bilateral postaxial polydactyly, mid-facial hypoplasia, high palatal arch, micropenis, and bilateral cryptorchidism."

Case-level documentation of bilateral postaxial polydactyly with the characteristic midfacial and genital findings.

Nervous System 2

Holoprosencephaly OCCASIONAL HP:0001360

Show evidence (2 references)

PMID:34921505 SUPPORT Human Clinical

"a morbidity spectrum that includes hypopituitarism (58%), HPE (6%)"

HPE in 6% of 60 individuals with pathogenic GLI2 variants maps to OCCASIONAL (5-29%).

PMID:24744436 SUPPORT Human Clinical

"only 1 of 43 had frank HPE"

An independent series reports frank HPE in only 1 of 43 truncating-variant carriers, confirming its rarity.

Seizures HP:0001250

Show evidence (1 reference)

PMID:20685856 SUPPORT Human Clinical

"The index case of family 1 had polydactyly, hypoglycemia, and seizures"

Documents seizures in a GLI2 mutation-positive proband.

Growth 1

Short stature FREQUENT HP:0004322

Show evidence (2 references)

PMID:14581620 SUPPORT Human Clinical

"Proband in family 2 with extreme midfacial hypoplasia, pseudomedian cleft lip, and severe growth retardation."

Documents severe growth failure in a GLI2 mutation-positive proband.

PMID:25878059 SUPPORT Human Clinical

"the phenotype frequently included GH deficiency"

GH deficiency - and hence growth failure - is a frequent component of the truncating-variant phenotype, supporting the FREQUENT band.

Other 11

Hypopituitarism FREQUENT HP:0040075

Show evidence (2 references)

PMID:34921505 SUPPORT Human Clinical

"We analyze the phenotypic descriptions of 60 individuals with pathogenic GLI2 variants and evidence a morbidity spectrum that includes hypopituitarism (58%)"

Hypopituitarism in 58% of 60 individuals with pathogenic GLI2 variants maps to FREQUENT (30-79%).

PMID:39938560 SUPPORT Human Clinical

"Most patients with a GLI2 variant (21/23, 91%) had hypopituitarism"

An endocrine-ascertained cohort reports a much higher figure (91%); the FREQUENT band follows the less ascertainment-biased Corder series.

Panhypopituitarism HP:0000871

Show evidence (1 reference)

PMID:14581620 SUPPORT Human Clinical

"whose primary features include defective anterior pituitary formation and pan-hypopituitarism"

Panhypopituitarism is named as a primary feature of GLI2 loss-of-function disease.

Central hypothyroidism HP:0011787

Show evidence (1 reference)

PMID:20685856 SUPPORT Human Clinical

"GH, TSH, prolactin, ACTH, LH, and FSH deficiencies"

TSH deficiency is documented as part of the multi-axis deficiency in a GLI2 proband.

Central adrenal insufficiency HP:0011734

Show evidence (1 reference)

PMID:20685856 SUPPORT Human Clinical

"In family 3, a girl had hypoglycemia, seizures, excessive thirst and polyuria, and GH, ACTH, TSH, and antidiuretic hormone deficiencies."

Documents ACTH deficiency alongside hypoglycaemia in a GLI2 mutation carrier.

Branchial arch anomaly Branchial anomaly HP:0009794

Show evidence (1 reference)

PMID:21204792 SUPPORT Human Clinical

"anophthalmia plus orbital anomalies, heminasal aplasia, branchial arch anomalies and polydactyly have also been incorporated into the general phenotype"

Branchial arch anomalies are an established component of the GLI2 phenotype.

Temporomandibular joint anomaly Abnormality of the temporomandibular joint HP:0010754

Show evidence (1 reference)

PMID:21204792 SUPPORT Human Clinical

"Novel sequence variants were found in the GLI2 gene in patients with marked involvement of the temporomandibular joint (TMJ), a new clinical finding observed with mutations of this gene."

The only report of TMJ involvement in GLI2 disease, from a single six-patient series; no frequency is recorded because no proportion is available.

Semilobar holoprosencephaly HP:0002507

Show evidence (1 reference)

PMID:21204792 SUPPORT Human Clinical

"phenotypic manifestations that range from isolated cleft lip/palate with polydactyly, branchial arch anomalies to semi-lobar holoprosencephaly"

Semilobar holoprosencephaly is the severe end of the range in this GLI2 mutation-positive series.

Neurocognitive impairment FREQUENT Neurodevelopmental abnormality HP:0012759

Show evidence (2 references)

PMID:39938560 SUPPORT Human Clinical

"The remaining signs included neurocognitive disorders (38%), hexadactyly (27%), cardiac septal defects, and renal/vesical abnormalities."

Neurocognitive disorders in 38% of the cohort maps to FREQUENT (30-79%).

PMID:22106008 SUPPORT Human Clinical

"a mild holoprosencephaly spectrum phenotype (bilateral cleft lip and palate and abnormal pituitary gland formation with panhypopituitarism) and normal psychomotor development"

Counter-example showing normal psychomotor development in a GLI2 deletion carrier without brain malformation; marked PARTIAL because it qualifies the frequency rather than supporting it.

Neonatal hypoglycemia HP:0001998

Show evidence (1 reference)

PMID:31782289 SUPPORT Human Clinical

"The index case was a boy who developed cholestasis and hypoglycaemia in the neonatal period."

Neonatal hypoglycaemia (with cholestasis) as the presenting feature of GLI2 multiple pituitary hormone deficiency.

Anophthalmia or microphthalmia HP:0000528

Show evidence (1 reference)

PMID:21204792 SUPPORT Human Clinical

"Subsequently, anophthalmia plus orbital anomalies, heminasal aplasia, branchial arch anomalies and polydactyly have also been incorporated into the general phenotype."

Anophthalmia with orbital anomalies is an established but uncommon part of the GLI2 phenotype.

Cardiac septal defect Abnormal cardiac septum morphology HP:0001671

Show evidence (1 reference)

PMID:39938560 SUPPORT Human Clinical

"In addition to polydactyly and neurocognitive disorders, cardiac and renal abnormalities were also frequently observed and should be investigated further."

Cardiac abnormalities are reported among the extrapituitary features. The source calls them "frequently observed" but gives no proportion for cardiac involvement specifically, so no frequency band is recorded.

🧬

Genetic Associations

1

GLI2

Gene: GLI2 hgnc:4318 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (3 references)

PMID:14581620 SUPPORT Human Clinical

"Here, we show that loss-of-function mutations in the human GLI2 gene are associated with a distinctive phenotype (within the HPE spectrum) whose primary features include defective anterior pituitary formation and pan-hypopituitarism, with or without overt forebrain cleavage abnormalities, and..."

The founding report establishing GLI2 loss of function as the cause of this distinctive HPE-spectrum phenotype.

PMID:34921505 SUPPORT Human Clinical

"We show that most of the 31 missense variants previously reported as pathogenic are likely benign or, at most, low-risk variants."

Reclassification of the missense variant burden; important for interpreting the historically high reported frequency of GLI2 "variants" in HPE cohorts.

PMID:22106008 SUPPORT Human Clinical

"Our findings confirm the association of haploinsufficiency of GLI2 and mild HPE spectrum features."

A 1.3 Mb 2q14.2 deletion encompassing GLI2 reproduces the phenotype, establishing gene dosage (haploinsufficiency) rather than an allele-specific effect as the disease mechanism.

Variants (3)

Truncating GLI2 variants removing the C-terminal activator domain

Nonsense, frameshift and canonical splice-site variants that truncate GLI2 before or within the C-terminal transcriptional activator domain are the best-established pathogenic class and carry the highest risk of hypopituitarism and polydactyly.

Show evidence (2 references)

PMID:20685856 SUPPORT Human Clinical

"All predict a truncated protein with loss of the C-terminal activator domain."

Three novel frameshift/nonsense GLI2 variants all remove the C-terminal activator domain, defining the canonical pathogenic variant class.

PMID:34921505 SUPPORT Human Clinical

"We establish that truncating and Zn-finger variants in GLI2 are associated with a high risk of hypopituitarism, and that a solitary median maxillary central incisor is part of the GLI2-related phenotypic variability."

Genotype-phenotype analysis of 60 individuals identifying truncating and zinc-finger variants as the two pathogenic classes.

Zinc-finger domain missense variants

A minority of missense variants located in the C2H2 zinc-finger DNA-binding domain are pathogenic, including p.(Arg479Gly), p.(Arg516Pro), p.(Gly518Lys) and p.(Tyr575His); functional assays show reduced transcriptional activity.

Show evidence (2 references)

PMID:34921505 SUPPORT Human Clinical

"Four Zn-finger variants: p.(Arg479Gly), p.(Arg516Pro), p.(Gly518Lys), and p.(Tyr575His) were classified as likely pathogenic"

Names the four zinc-finger missense variants that survive stringent reclassification as likely pathogenic.

PMID:30548673 SUPPORT In Vitro

"The in vitro functional study of the plasmids bearing two of the three missense variants (namely p.Tyr575His and p.Ala593Val) revealed a significant reduction in transcriptional activity."

Luciferase reporter assays provide direct in vitro evidence that these missense variants reduce GLI2 transcriptional activity.

2q14.2 deletions encompassing GLI2

Submicroscopic and larger interstitial deletions of 2q14.2 that remove GLI2 produce a phenotype continuous with that of intragenic truncating variants, with incomplete penetrance within the same family.

Show evidence (1 reference)

PMID:22106008 SUPPORT Human Clinical

"We report here on a patient with a mild holoprosencephaly spectrum phenotype (bilateral cleft lip and palate and abnormal pituitary gland formation with panhypopituitarism) and normal psychomotor development, who was found to carry a 1.3 Mb submicroscopic heterozygous deletion in 2q14.2,..."

A whole-gene deletion produces the mild HPE-spectrum phenotype, supporting dosage sensitivity.

💊

Medical Actions

5

Growth hormone replacement

Action: Pharmacotherapy NCIT:C15986

Agent: somatropin NCIT:C837

Recombinant human growth hormone (somatropin) for the growth hormone deficiency that is the most consistent hormonal deficit, restoring growth velocity and final height.

Target Phenotypes: Short stature HP:0004322

Show evidence (1 reference)

PMID:36936162 SUPPORT Human Clinical

"Once diagnosed, individualized hormone replacement treatment is required for each patient."

Individualised hormone replacement is the management principle for GLI2-related (Culler-Jones) disease.

Multi-axis pituitary hormone replacement

Action: Pharmacotherapy NCIT:C15986

Agent: hydrocortisone CHEBI:17650 levothyroxine CHEBI:18332 desmopressin CHEBI:4450

Replacement of the remaining deficient axes as identified - hydrocortisone for ACTH deficiency (with stress dosing and adrenal crisis education, the most safety-critical element), levothyroxine for central hypothyroidism, desmopressin for central diabetes insipidus, and sex steroids at the age of puberty for hypogonadotropic hypogonadism.

Target Phenotypes: Hypopituitarism HP:0040075

Show evidence (1 reference)

PMID:20685856 SUPPORT Human Clinical

"These phenotypes support partial penetrance, variable polydactyly, midline facial defects, and pituitary hormone deficiencies, including diabetes insipidus, conferred by heterozygous frameshift or nonsense GLI2 mutations."

Establishes the range of hormone axes - including ADH - that require replacement in GLI2-related disease.

Surgical correction of postaxial polydactyly

Action: Orthopedic surgical procedure Ontology label: Orthopedic Surgical Procedure NCIT:C16186

Excision or reconstruction of the supernumerary postaxial digit, usually in infancy or early childhood, for function and appearance. This is standard orthopaedic practice rather than a GLI2-specific intervention.

Target Phenotypes: Postaxial polydactyly HP:0100259

Show evidence (1 reference)

PMID:34921505 SUPPORT Human Clinical

"The most prevalent phenotypic feature is post-axial polydactyly (65%)"

Establishes the frequency of the anomaly this treatment addresses. Marked PARTIAL because the source documents the indication, not the intervention.

Cleft lip and palate repair

Action: Surgical procedure Ontology label: Surgical Procedure NCIT:C15329

Staged surgical repair of cleft lip and palate along standard craniofacial protocols, with speech and feeding support.

Target Phenotypes: Orofacial cleft HP:0000202

Show evidence (1 reference)

PMID:34921505 SUPPORT Human Clinical

"orofacial clefting (17%)"

Establishes the frequency of the anomaly this treatment addresses. Marked PARTIAL because repair follows generic craniofacial protocols not evaluated in this source.

Genetic counselling

Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Counselling must address the two facts that make GLI2 unusual: a phenotypically normal parent may carry the variant (so a negative family history does not lower recurrence risk), and a carrier child's phenotype cannot be predicted from the genotype. Cascade testing and the reclassification of most GLI2 missense variants as benign are both central to the discussion.

Show evidence (2 references)

PMID:34921505 SUPPORT Human Clinical

"Our approach clarifies clinical risks and the important messages to discuss in counseling for a pathogenic GLI2 variant."

Frames genotype-informed counselling as the explicit clinical deliverable of GLI2 genotype-phenotype analysis.

PMID:25878059 SUPPORT Human Clinical

"The mutation was frequently inherited from an asymptomatic parent."

The counselling fact that most complicates recurrence-risk discussion.

🌍

Environmental Factors

3

Maternal pregestational diabetes

The most consistently replicated non-genetic risk factor for holoprosencephaly in human epidemiology, and therefore the leading candidate second hit for a dose-limited GLI2 carrier. The evidence is for holoprosencephaly broadly rather than for GLI2 carriers specifically - no study has yet stratified maternal diabetes risk by GLI2 genotype, which is precisely what the exp_gli2_prospective_periconceptional_exposure_cohort experiment proposes.

Show evidence (2 references)

PMID:29761639 SUPPORT Human Clinical

"A 2010 review of the literature identified several risk factors that had been consistently identified as occurring more frequently among cases of HPE, including maternal diabetes, twinning, and a predominance of females"

A CDC systematic review of the epidemiologic literature identifies maternal diabetes as one of the risk factors consistently associated with holoprosencephaly.

PMID:33111505 SUPPORT Human Clinical

"Pregnancy associated risk associated with holoprosencephaly included maternal pregestational diabetes (9.2% of cases and 0 controls, p = .02)"

A case-control study quantifies the association: pregestational diabetes in 9.2% of holoprosencephaly cases versus none of the controls.

Mechanism Target:

PREDISPOSES Reduced Developmental Buffering of the Hedgehog Pathway — This entry models a dose-limited pathway with no reserve, which is the substrate on which environmental insults act. Maternal diabetes is the best-replicated such insult and raises the chance that a carrier crosses into the affected range.

Show evidence (1 reference)

PMID:33111505 SUPPORT Human Clinical

"Pregnancy associated risk associated with holoprosencephaly included maternal pregestational diabetes (9.2% of cases and 0 controls, p = .02)"

Reports maternal pregestational diabetes in 9.2% of holoprosencephaly cases versus none of the controls, a human association with the malformation.

Prenatal ethanol exposure

Prenatal alcohol exposure interacts with reduced Gli2 dose in the mouse, substantially amplifying craniofacial dysmorphology and producing holoprosencephaly-spectrum defects that the exposure alone does not cause. It is a candidate second hit for the incomplete penetrance seen in human GLI2 carriers, though the interaction has not been demonstrated directly in humans.

Show evidence (1 reference)

PMID:24586787 SUPPORT Model Organism

"Following ethanol exposure, mean dysmorphology scores were increased by 3.2- and 6.6-fold in Shh(+/-) and Gli2(+/-) groups, respectively, relative to their wildtype littermates."

Quantifies the gene-environment amplification of ethanol teratogenicity by Gli2 haploinsufficiency in mice.

Mechanism Target:

EXACERBATES Reduced Developmental Buffering of the Hedgehog Pathway — Ethanol worsens the phenotype specifically on a Hedgehog-sensitised background, which is what this node describes: the same dose produces far more dysmorphology when one Shh or Gli2 allele is already lost.

Show evidence (1 reference)

PMID:24586787 SUPPORT Model Organism

"Following ethanol exposure, mean dysmorphology scores were increased by 3.2- and 6.6-fold in Shh(+/-) and Gli2(+/-) groups, respectively, relative to their wildtype littermates."

Ethanol raised dysmorphology scores several-fold in Shh and Gli2 heterozygotes relative to wild type, demonstrating the gene-environment interaction. Support is PARTIAL because the demonstration is in mice and has not been shown in human carriers.

Teratogen exposure during first-trimester patterning

Low-dose exposure to a Hedgehog-pathway-antagonising teratogen converts silent Gli2 heterozygosity into overt holoprosencephaly in the mouse, the general form of the second-hit model for this disorder.

Show evidence (1 reference)

PMID:27585885 SUPPORT Model Organism

"mice with single-allele Gli2 mutations exhibit increased penetrance and severity of HPE in response to low-dose teratogen exposure"

Establishes low-dose teratogen exposure as the environmental arm of the gene-environment interaction.

Mechanism Target:

EXACERBATES Reduced Developmental Buffering of the Hedgehog Pathway — Low-dose teratogen exposure that a normal embryo tolerates becomes damaging once buffering is lost, increasing both penetrance and severity. This is the mechanism by which an unaffected carrier parent can have a severely affected child.

Show evidence (1 reference)

PMID:27585885 SUPPORT Model Organism

"mice with single-allele Gli2 mutations exhibit increased penetrance and severity of HPE in response to low-dose teratogen exposure"

Single-allele Gli2 mutant mice showed increased penetrance and severity of holoprosencephaly after low-dose teratogen exposure. Support is PARTIAL because this is a mouse demonstration rather than human data.

🔬

Diagnosis

4

Pituitary MRI

Dedicated sellar/pituitary MRI is the key structural investigation, looking for the anterior pituitary hypoplasia, ectopic posterior lobe and absent stalk that characterise GLI2-related hypopituitarism, and for any coexisting holoprosencephaly-spectrum forebrain malformation.

Show evidence (1 reference)

PMID:20685856 SUPPORT Human Clinical

"Magnetic resonance imaging of four patients with GLI2 mutations and hypopituitarism showed a hypoplastic anterior pituitary and an ectopic posterior pituitary lobe without HPE."

Establishes the MRI pattern that should prompt GLI2 testing.

Anterior pituitary hormone assessment

Baseline and dynamic endocrine testing across the GH, ACTH-cortisol, TSH-thyroxine, gonadotropin and prolactin axes, plus assessment for diabetes insipidus, to define which axes are deficient and guide replacement.

Show evidence (1 reference)

PMID:20685856 SUPPORT Human Clinical

"GH, TSH, prolactin, ACTH, LH, and FSH deficiencies"

The multi-axis deficiency pattern that hormone assessment is designed to detect.

GLI2 molecular testing

Sequencing of GLI2, usually within a holoprosencephaly or congenital hypopituitarism gene panel or by exome sequencing, with chromosomal microarray when a 2q14.2 deletion is suspected. Cascade testing of apparently unaffected relatives is informative because of the marked non-penetrance. Interpretation must account for the reclassification of most previously reported GLI2 missense variants as benign or low risk.

Show evidence (2 references)

PMID:29771000 SUPPORT Human Clinical

"Traditionally, the genetic workup for HPE has been a karyotype, chromosomal microarray, and/or Sanger sequencing of select genes."

Describes the molecular testing framework for holoprosencephaly within which GLI2 testing sits.

PMID:34921505 SUPPORT Human Clinical

"We show that most of the 31 missense variants previously reported as pathogenic are likely benign or, at most, low-risk variants."

Directly informs variant interpretation: most historically reported GLI2 missense variants should not be called pathogenic.

Chromosomal microarray

Copy-number analysis, indicated when a contiguous 2q14.2 deletion is suspected - the structural-variant counterpart of the 2q14.2 deletion class in the genetic section. Sequencing alone will miss a whole-gene deletion, and the deletion phenotype is continuous with that of intragenic truncating variants, so a negative GLI2 sequencing result does not exclude GLI2 as the cause.

Show evidence (2 references)

PMID:29771000 SUPPORT Human Clinical

"Traditionally, the genetic workup for HPE has been a karyotype, chromosomal microarray, and/or Sanger sequencing of select genes."

Places chromosomal microarray in the standard holoprosencephaly genetic workup alongside sequencing.

PMID:22106008 SUPPORT Human Clinical

"Large, microscopically visible, interstitial deletions spanning 2q14.2 have been reported in patients with multiple congenital anomalies and intellectual disability."

Documents the 2q14.2 deletion class that copy-number analysis is needed to detect.

🩻

Imaging Findings

3

Anterior pituitary hypoplasia

A small anterior pituitary lobe on sagittal MRI, the structural correlate of the hormone deficiency.

Mri Diagnostic

Anterior pituitary hypoplasia HP:0010627

Show evidence (1 reference)

PMID:20685856 SUPPORT Human Clinical

"Magnetic resonance imaging of four patients with GLI2 mutations and hypopituitarism showed a hypoplastic anterior pituitary and an ectopic posterior pituitary lobe without HPE."

Direct MRI documentation of anterior pituitary hypoplasia in GLI2 mutation carriers.

Ectopic posterior pituitary

An undescended posterior pituitary bright spot at or near the median eminence rather than in the sella - together with a hypoplastic anterior lobe and absent stalk this constitutes the pituitary stalk interruption pattern that is highly characteristic of GLI2-related hypopituitarism.

Mri Diagnostic

Ectopic posterior pituitary HP:0011755

Show evidence (2 references)

PMID:22967285 SUPPORT Human Clinical

"The posterior pituitary lobe on MRI was ectopic in 16, not visible in 4, normally placed in 2 and imaging was not available in two patients, but there were no signs of holoprosencephaly."

In a GLI2-variant hypopituitarism series the posterior lobe was ectopic in the large majority, with no holoprosencephaly.

PMID:39938560 SUPPORT Human Clinical

"Pituitary morphological abnormalities were present in 84% of the patients with P GLI2 variants"

Quantifies how consistently structural pituitary abnormality accompanies a pathogenic GLI2 variant.

Interrupted pituitary stalk

Absent or interrupted pituitary stalk, completing the pituitary stalk interruption syndrome pattern, characteristically without any other midline structural abnormality.

Mri

Interrupted pituitary stalk HP:0034978

Show evidence (1 reference)

PMID:31782289 SUPPORT Human Clinical

"There was severe anterior pituitary hypoplasia, absent pituitary stalk and ectopic posterior pituitary on magnetic resonance imaging which suggested pituitary stalk interruption syndrome with no other midline structural abnormality."

Documents the full stalk-interruption triad in a GLI2 splice-variant carrier.

📈

Progression

1

The structural anomalies - forebrain, craniofacial and limb - are fixed at birth and do not progress. The endocrine phenotype is congenital in origin but may declare itself over time: neonatal hypoglycaemia and cholestasis, then growth failure in childhood, then absent or delayed puberty. Hormone deficiencies are lifelong and require continuing replacement rather than resolving; the presence and severity of structural brain malformation, not the endocrine deficit, is the dominant determinant of neurodevelopmental outcome.

Show evidence (2 references)

PMID:31782289 SUPPORT Human Clinical

"The index case was a boy who developed cholestasis and hypoglycaemia in the neonatal period."

Illustrates the neonatal end of the temporal sequence of endocrine presentation.

PMID:33235745 SUPPORT Human Clinical

"Sisters 1 and 2 present with the classic dyad of findings in a patient with Culler Jones syndrome of growth hormone (GH) deficiency and postaxial polydactyly, and their mother also demonstrated postaxial polydactyly at birth but otherwise has an unremarkable phenotype."

Shows the childhood presentation (GH deficiency plus polydactyly) alongside a lifelong-stable minimal phenotype in the carrier mother.

📊

Prevalence

2

Worldwide (holoprosencephaly, all causes)

Birth Prevalence 3.2 per 100,000 (2.6–3.8) 1–9 per 100,000

Context figure for holoprosencephaly as a whole, not for HPE9. Japanese nationwide survey estimate of 0.32 per 10,000 live births (95% CI 0.26-0.38), equivalent to 3.2 per 100,000; international estimates for HPE overall span 0.10-6.06 per 10,000 births.

Show evidence (2 references)

PMID:31886593 SUPPORT Human Clinical

"the estimated BPR of HPE was calculated to be 0.32 per 10 000 live births (95% CI: 0.26-0.38)"

Nationwide Japanese birth-prevalence estimate for holoprosencephaly overall.

PMID:31886593 SUPPORT Human Clinical

"Holoprosencephaly (HPE) is a congenital malformation with an estimated prevalence of 0.10-6.06 per 10 000 births"

Gives the international range of reported HPE birth prevalence.

🔀

Differential Diagnoses

5

Conditions with similar clinical presentations that must be differentiated from Holoprosencephaly 9:

Non-syndromic pituitary stalk interruption syndrome

Overlapping Features The identical MRI triad of anterior pituitary hypoplasia, ectopic posterior lobe and absent stalk arises from many causes; the presence of postaxial polydactyly or midline facial features is what should redirect testing toward GLI2.

Show evidence (1 reference)

PMID:39938560 SUPPORT Human Clinical

"All these GLI2 variants were identified in 23 patients (17 index cases and 6 relatives) with associated pituitary stalk interruption syndrome or extrapituitary manifestations."

Every pathogenic GLI2 variant in this cohort carried either stalk interruption or an extrapituitary feature, so an isolated stalk-interruption picture without extrapituitary findings points away from GLI2.

Other genetic causes of combined pituitary hormone deficiency

Overlapping Features HESX1, LHX3, LHX4, OTX2, PROP1, POU1F1 and SOX3 among others. GLI2 is distinguished by its extrapituitary features - polydactyly above all - and is now the most frequently identified cause of the syndromic form.

Show evidence (1 reference)

PMID:39938560 SUPPORT Human Clinical

"GLI2 was the most frequently identified genetic cause of syndromic CH with constant association of pituitary stalk interruption syndrome or extrapituitary clinical features."

Positions GLI2 relative to the other congenital hypopituitarism genes and names the features that distinguish it.

Smith-Lemli-Opitz syndrome

Overlapping Features A cholesterol biosynthesis defect that phenocopies Hedgehog pathway disruption, with holoprosencephaly-spectrum midline defects, polydactyly and genital anomalies, but is autosomal recessive and biochemically diagnosable by elevated 7-dehydrocholesterol.

Show evidence (1 reference)

PMID:14581620 SUPPORT Model Organism

"Pharmacological inhibition of cholesterol synthesis in rats, which inhibits Hh signaling, can cause HPE-like findings including alterations in pituitary formation"

Establishes the mechanistic basis for the phenocopy - blocking cholesterol synthesis inhibits Hedgehog signalling and reproduces HPE-like pituitary findings. Marked PARTIAL because the rat experiment models the pathway overlap rather than documenting Smith-Lemli-Opitz syndrome itself.

🐁

Animal Models

4

Gli2 homozygous null Mus musculus

Homozygous Gli2 loss of function on the C57BL/6J background reproduces the brain and facial features of severe human holoprosencephaly, including midfacial hypoplasia, hypotelorism and medial forebrain deficiency. The same genotype on other backgrounds does not, making this the clearest demonstration that genetic background modifies holoprosencephaly penetrance.

Species

Mus musculus

Genotype

Gli2 homozygous null

Background

C57BL/6J

Show evidence (1 reference)

PMID:27585885 SUPPORT Model Organism

"On the C57BL/6J background, homozygous GLI2 loss of function results in the characteristic brain and facial features seen in severe human HPE, including midfacial hypoplasia, hypotelorism and medial forebrain deficiency with loss of ventral neurospecification."

Background-dependent recapitulation of the severe human phenotype.

Gli2 heterozygous null Mus musculus

The model closest to the human carrier state: phenotypically normal at baseline, but with a dosage-dependent attenuation of Hedgehog ligand responsiveness that predisposes to holoprosencephaly on teratogen or ethanol challenge.

Species

Mus musculus

Genotype

Gli2 heterozygous null

Show evidence (1 reference)

PMID:27585885 SUPPORT Model Organism

"Although normally indistinguishable from wild-type littermates, we demonstrate that mice with single-allele Gli2 mutations exhibit increased penetrance and severity of HPE in response to low-dose teratogen exposure."

Directly models the human situation of a silent heterozygous carrier who can nevertheless transmit or manifest disease.

Gli2 homozygous null (CNS floor plate) Mus musculus

Gli2 null embryos fail to form a floor plate throughout the midbrain, hindbrain and spinal cord, and lose the cell populations flanking the floor plate, while most ventral neuron classes still form - establishing Gli2 as required specifically for ventral midline induction.

Species

Mus musculus

Genotype

Gli2 homozygous null (CNS floor plate)

Show evidence (1 reference)

PMID:9655799 SUPPORT Model Organism

"We have found that the floor plate throughout the midbrain, hindbrain and spinal cord does not form in Gli2 homozygotes."

Defines the specific ventral-midline requirement for Gli2 in the CNS.

you-too (yot) gli2 mutant Danio rerio

Zebrafish yot mutants, which carry dominant-negative forms of Gli2, develop a lens from the adenohypophyseal anlage, showing that Shh-Gli signalling is required to maintain pituitary rather than lens identity in the anterior midline.

Species

Danio rerio

Genotype

you-too (yot) gli2 mutant

Show evidence (1 reference)

PMID:10960781 SUPPORT Model Organism

"We show here that the zebrafish midline mutants you-too (yot) and iguana (igu) develop lenses from the adenohypophysis anlage."

Model-organism evidence for a Gli2-dependent step in adenohypophyseal fate specification.

{ }

Source YAML

click to show

name: Holoprosencephaly 9
creation_date: "2026-07-30T00:00:00Z"
category: Mendelian
disease_term:
  preferred_term: holoprosencephaly 9
  term:
    id: MONDO:0012563
    label: holoprosencephaly 9
synonyms:
- HPE9
- GLI2 holoprosencephaly
- GLI2-related holoprosencephaly
- holoprosencephaly with microphthalmia and first branchial arch anomalies
- pituitary anomalies with holoprosencephaly-like features
- Culler-Jones syndrome
references:
- reference: PMID:20301702
  title: "Holoprosencephaly Overview"
  tags:
  - GeneReviews
description: >-
  Holoprosencephaly 9 (HPE9) is an autosomal dominant developmental disorder caused
  by heterozygous loss-of-function variants in GLI2, the principal transcriptional
  activator of the Sonic hedgehog (SHH) signalling pathway. Despite the
  "holoprosencephaly" designation, frank forebrain non-cleavage is the exception
  rather than the rule: the characteristic presentation is an HPE-like phenotype
  dominated by pituitary anomalies (hypopituitarism/combined pituitary hormone
  deficiency with a hypoplastic anterior pituitary and ectopic posterior pituitary
  lobe), postaxial polydactyly, and subtle midline craniofacial features (midface
  hypoplasia, orofacial clefting, hypotelorism, solitary median maxillary central
  incisor). First branchial arch and temporomandibular joint anomalies, orbital
  anomalies, and - in a small minority - semilobar or lobar holoprosencephaly
  complete the spectrum. Penetrance is markedly incomplete and expressivity highly
  variable, with pathogenic alleles frequently inherited from a mildly affected or
  entirely asymptomatic parent; mouse work shows that a single functional Gli2
  allele attenuates Hedgehog ligand responsiveness and predisposes to overt
  holoprosencephaly only when a second (environmental) hit is applied, providing a
  mechanistic account of that non-penetrance. The same GLI2 loss-of-function allelic
  series is also catalogued as Culler-Jones syndrome and is now the single most
  frequently identified genetic cause of syndromic congenital hypopituitarism.
parents:
- Congenital Disorder
- Neurodevelopmental Disorder

classifications:
  harrisons_chapter:
  - classification_value: ENDOCRINOLOGY_METABOLISM
    notes: >-
      The dominant clinical presentation is congenital hypopituitarism / combined
      pituitary hormone deficiency, and most reported carriers are ascertained
      through endocrine rather than neurology clinics.
  - classification_value: NEUROLOGIC
    notes: >-
      A minority of carriers have frank holoprosencephaly-spectrum forebrain
      malformation, and neurocognitive impairment is reported in a substantial
      subset.
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    notes: >-
      Autosomal dominant Mendelian disorder with markedly incomplete penetrance;
      the mouse Gli2 haploinsufficiency-plus-teratogen model makes this an explicit
      gene-environment interaction disorder.

inheritance:
- name: Autosomal dominant
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  penetrance: INCOMPLETE
  expressivity: VARIABLE
  description: >-
    Heterozygous GLI2 loss-of-function alleles segregate in an autosomal dominant
    pattern, but penetrance is strikingly incomplete: pathogenic variants are
    frequently transmitted by an asymptomatic parent, or by a parent whose only
    manifestation is postaxial polydactyly. A substantial minority of probands
    carry a de novo variant.
  evidence:
  - reference: PMID:25878059
    reference_title: "Role of GLI2 in hypopituitarism phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The inheritance pattern was autosomal dominant with incomplete penetrance
      and variable expressivity. The mutation was frequently inherited from an
      asymptomatic parent.
    explanation: >-
      A review of 25 patients in 16 families with heterozygous truncating GLI2
      mutations establishes autosomal dominant inheritance with incomplete
      penetrance and frequent transmission from an unaffected carrier parent.
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Substantial phenotypic variability and nonpenetrance have been described,
      posing difficulties in the counseling of affected families.
    explanation: >-
      Confirms non-penetrance and phenotypic variability as the central
      counselling problem in GLI2-related disease.
  - reference: PMID:33235745
    reference_title: "A case series of a mother and two daughters with a GLI2 gene deletion demonstrating variable expressivity and incomplete penetrance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This case series and review of the literature support that patients with
      pathogenic variants of the GLI2 gene demonstrate an autosomal dominant
      inheritance pattern, variable expressivity, and incomplete penetrance.
    explanation: >-
      A three-generation family with a shared GLI2 deletion directly demonstrates
      the dominant inheritance, variable expressivity and incomplete penetrance.
  - reference: PMID:39938560
    reference_title: "Phenotype and genotype of 23 patients with hypopituitarism and pathogenic GLI2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      88% (15/17) of mutations were truncating variants, and 45% were de novo.
    explanation: >-
      Quantifies the de novo rate in the largest multicentre cohort of pathogenic
      GLI2 variants, complementing the familial-transmission data.

genetic:
- name: GLI2
  gene_term:
    preferred_term: GLI2
    term:
      id: hgnc:4318
      label: GLI2
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  features: >-
    GLI2 (2q14.2) encodes a C2H2 zinc-finger transcription factor that is the
    principal activator arm of the Hedgehog pathway. Pathogenic alleles are
    predominantly truncating (nonsense, frameshift, canonical splice) and remove
    the C-terminal transcriptional activator domain; whole-gene and contiguous
    2q14.2 deletions produce the same phenotype. Zinc-finger missense variants are
    a second, smaller pathogenic class, whereas most previously reported missense
    variants have been reclassified as benign or low-risk.
  notes: >-
    GLI2 is also somatically activated in Hedgehog-driven cancers (e.g.
    medulloblastoma, basal cell carcinoma); that gain-of-signal role is
    mechanistically opposite to the loss-of-function developmental disorder curated
    here.
  evidence:
  - reference: PMID:14581620
    reference_title: "Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we show that loss-of-function mutations in the human GLI2 gene are
      associated with a distinctive phenotype (within the HPE spectrum) whose
      primary features include defective anterior pituitary formation and
      pan-hypopituitarism, with or without overt forebrain cleavage abnormalities,
      and HPE-like midfacial hypoplasia.
    explanation: >-
      The founding report establishing GLI2 loss of function as the cause of this
      distinctive HPE-spectrum phenotype.
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We show that most of the 31 missense variants previously reported as
      pathogenic are likely benign or, at most, low-risk variants.
    explanation: >-
      Reclassification of the missense variant burden; important for interpreting
      the historically high reported frequency of GLI2 "variants" in HPE cohorts.
  - reference: PMID:22106008
    reference_title: "A patient with a mild holoprosencephaly spectrum phenotype and heterotaxy and a 1.3 Mb deletion encompassing GLI2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our findings confirm the association of haploinsufficiency of GLI2 and mild
      HPE spectrum features.
    explanation: >-
      A 1.3 Mb 2q14.2 deletion encompassing GLI2 reproduces the phenotype,
      establishing gene dosage (haploinsufficiency) rather than an allele-specific
      effect as the disease mechanism.
  variants:
  - name: Truncating GLI2 variants removing the C-terminal activator domain
    description: >-
      Nonsense, frameshift and canonical splice-site variants that truncate GLI2
      before or within the C-terminal transcriptional activator domain are the
      best-established pathogenic class and carry the highest risk of
      hypopituitarism and polydactyly.
    evidence:
    - reference: PMID:20685856
      reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        All predict a truncated protein with loss of the C-terminal activator
        domain.
      explanation: >-
        Three novel frameshift/nonsense GLI2 variants all remove the C-terminal
        activator domain, defining the canonical pathogenic variant class.
    - reference: PMID:34921505
      reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        We establish that truncating and Zn-finger variants in GLI2 are associated
        with a high risk of hypopituitarism, and that a solitary median maxillary
        central incisor is part of the GLI2-related phenotypic variability.
      explanation: >-
        Genotype-phenotype analysis of 60 individuals identifying truncating and
        zinc-finger variants as the two pathogenic classes.
  - name: Zinc-finger domain missense variants
    description: >-
      A minority of missense variants located in the C2H2 zinc-finger DNA-binding
      domain are pathogenic, including p.(Arg479Gly), p.(Arg516Pro), p.(Gly518Lys)
      and p.(Tyr575His); functional assays show reduced transcriptional activity.
    evidence:
    - reference: PMID:34921505
      reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Four Zn-finger variants: p.(Arg479Gly), p.(Arg516Pro), p.(Gly518Lys), and
        p.(Tyr575His) were classified as likely pathogenic
      explanation: >-
        Names the four zinc-finger missense variants that survive stringent
        reclassification as likely pathogenic.
    - reference: PMID:30548673
      reference_title: "Novel GLI2 mutations identified in patients with Combined Pituitary Hormone Deficiency (CPHD): Evidence for a pathogenic effect by functional characterization."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The in vitro functional study of the plasmids bearing two of the three
        missense variants (namely p.Tyr575His and p.Ala593Val) revealed a
        significant reduction in transcriptional activity.
      explanation: >-
        Luciferase reporter assays provide direct in vitro evidence that these
        missense variants reduce GLI2 transcriptional activity.
  - name: 2q14.2 deletions encompassing GLI2
    description: >-
      Submicroscopic and larger interstitial deletions of 2q14.2 that remove GLI2
      produce a phenotype continuous with that of intragenic truncating variants,
      with incomplete penetrance within the same family.
    evidence:
    - reference: PMID:22106008
      reference_title: "A patient with a mild holoprosencephaly spectrum phenotype and heterotaxy and a 1.3 Mb deletion encompassing GLI2."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        We report here on a patient with a mild holoprosencephaly spectrum
        phenotype (bilateral cleft lip and palate and abnormal pituitary gland
        formation with panhypopituitarism) and normal psychomotor development, who
        was found to carry a 1.3 Mb submicroscopic heterozygous deletion in
        2q14.2, encompassing the GLI2 gene.
      explanation: >-
        A whole-gene deletion produces the mild HPE-spectrum phenotype, supporting
        dosage sensitivity.

has_subtypes:
- name: Pituitary-Polydactyly
  display_name: Pituitary anomaly with postaxial polydactyly (Culler-Jones spectrum)
  subtype_term:
    preferred_term: Culler-Jones syndrome
    term:
      id: MONDO:0014369
      label: postaxial polydactyly-anterior pituitary anomalies-facial dysmorphism syndrome
  description: >-
    The predominant presentation of GLI2 loss of function: hypopituitarism
    (isolated GH deficiency through panhypopituitarism) with a hypoplastic anterior
    pituitary and ectopic posterior pituitary lobe, postaxial polydactyly, and
    subtle midfacial features, in the absence of any forebrain cleavage defect.
    Catalogued in its own right as Culler-Jones syndrome (OMIM 615849,
    MONDO:0014369, Orphanet 420584), which is grounded here as this subtype's
    subtype_term rather than split into a separate dismech entry - see the
    hpe9_nomenclature discussion for that decision.
  evidence:
  - reference: PMID:24744436
    reference_title: "Pathogenic mutations in GLI2 cause a specific phenotype that is distinct from holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Individuals with truncating mutations in GLI2 typically present with
      pituitary anomalies, polydactyly and subtle facial features rather than HPE.
    explanation: >-
      Defines the dominant, non-HPE presentation of GLI2 truncating variants.
  - reference: PMID:20685856
    reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Magnetic resonance imaging of four patients with GLI2 mutations and
      hypopituitarism showed a hypoplastic anterior pituitary and an ectopic
      posterior pituitary lobe without HPE.
    explanation: >-
      Establishes the characteristic pituitary imaging phenotype occurring without
      holoprosencephaly.
- name: HPE-spectrum
  display_name: GLI2-related holoprosencephaly (forebrain non-cleavage)
  description: >-
    The minority presentation in which GLI2 loss of function produces frank
    holoprosencephaly, most often semilobar, with the classic HPE facial features.
    Reported in roughly 6% of individuals with pathogenic GLI2 variants and in only
    1 of 43 carriers of truncating variants in an earlier series. No subtype_term is
    given because this tier has no MONDO class distinct from the entry's own
    disease_term: "GLI2-related disease with forebrain non-cleavage" simply is
    holoprosencephaly 9 (MONDO:0012563). Only the mild tier acquired a separate
    identifier, because it was historically split out as Culler-Jones syndrome.
  evidence:
  - reference: PMID:24744436
    reference_title: "Pathogenic mutations in GLI2 cause a specific phenotype that is distinct from holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      only 1 of 43 had frank HPE
    explanation: >-
      Quantifies how uncommon frank holoprosencephaly is among carriers of
      truncating GLI2 variants.
  - reference: PMID:21204792
    reference_title: "Clinical findings in patients with GLI2 mutations--phenotypic variability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here we described six Brazilian patients with phenotypic manifestations that
      range from isolated cleft lip/palate with polydactyly, branchial arch
      anomalies to semi-lobar holoprosencephaly.
    explanation: >-
      Documents the severe end of the spectrum (semilobar HPE) within a GLI2
      mutation-positive series.

pathophysiology:
- name: GLI2 Loss-of-Function Variant
  biological_scale: MOLECULAR
  role: trigger
  description: >-
    A heterozygous truncating variant, pathogenic zinc-finger missense variant, or
    whole-gene 2q14.2 deletion removes or inactivates one GLI2 allele. Truncating
    alleles delete the C-terminal transcriptional activation domain, so the
    residual protein cannot drive Hedgehog target-gene transcription.
  molecular_functions:
  - preferred_term: DNA-binding transcription factor activity
    term:
      id: GO:0003700
      label: DNA-binding transcription factor activity
    modifier: DECREASED
  downstream:
  - target: Reduced GLI2 Transcriptional Activator Dose
  evidence:
  - reference: PMID:20685856
    reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All predict a truncated protein with loss of the C-terminal activator
      domain.
    explanation: >-
      Identifies loss of the C-terminal activator domain as the shared molecular
      consequence of the pathogenic truncating alleles.
  - reference: PMID:14581620
    reference_title: "Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We also demonstrate that these mutations lack GLI2 activity.
    explanation: >-
      Frog-embryo and C3H10T1/2 osteogenic-induction assays show the patient
      alleles have no GLI2 activity, confirming loss of function.

- name: Reduced GLI2 Transcriptional Activator Dose
  biological_scale: MOLECULAR
  role: central_effector
  description: >-
    GLI2 is the principal activator among the three vertebrate GLI transcription
    factors that transduce the Hedgehog signal. With one allele inactivated, the
    dose of full-length GLI2 activator available for nuclear translocation and
    target-gene activation falls. The mutant alleles show no dominant-negative
    activity in the original functional assays, so the mechanism is
    haploinsufficiency rather than poisoning of the wild-type product - although a
    later C-terminal frameshift allele did display a dominant-negative effect,
    leaving room for allele-specific mechanisms.
  molecular_functions:
  - preferred_term: DNA-binding transcription factor activity
    term:
      id: GO:0003700
      label: DNA-binding transcription factor activity
    modifier: DECREASED
  downstream:
  - target: Attenuated Hedgehog Transcriptional Output
  evidence:
  - reference: PMID:14581620
    reference_title: "Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Gli2 is one of three vertebrate transcription factors implicated as
      obligatory mediators of Shh signal transduction.
    explanation: >-
      Places GLI2 as an obligatory transducer of the Hedgehog signal, the step
      that is dose-reduced here.
  - reference: PMID:14581620
    reference_title: "Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      None of the mutant alleles manifested dominant negative activity in these
      studies.
    explanation: >-
      Co-injection experiments with wild-type GLI2 found no dominant-negative
      activity, supporting simple haploinsufficiency.
  - reference: PMID:30629636
    reference_title: "A novel truncating variant of GLI2 associated with Culler-Jones syndrome impairs Hedgehog signalling."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Functional assays confirmed the pathogenicity of the identified variant and
      revealed a dominant-negative effect of mutant GLI2 on Hedgehog signalling.
    explanation: >-
      A C-terminal frameshift allele (p.P1167LfsX52) behaved as a dominant negative
      in cell-based assays, so haploinsufficiency may not be the mechanism for
      every pathogenic allele. Marked PARTIAL because it qualifies rather than
      supports the haploinsufficiency model.

- name: Attenuated Hedgehog Transcriptional Output
  biological_scale: CELLULAR
  role: central_effector
  description: >-
    Reduced GLI2 activator dose lowers transcriptional output of the Hedgehog
    pathway in responding cells. Mouse work shows this is not an all-or-nothing
    switch: Gli2 heterozygosity produces a dosage-dependent attenuation of
    Hedgehog ligand responsiveness at the cellular level, which is compatible with
    normal development at baseline but leaves the pathway with less reserve.
  biological_processes:
  - preferred_term: smoothened signaling pathway
    term:
      id: GO:0007224
      label: smoothened signaling pathway
    modifier: DECREASED
  cell_types:
  - preferred_term: neural progenitor cell
    term:
      id: CL:0011020
      label: neural progenitor cell
  cellular_components:
  - preferred_term: primary cilium
    term:
      id: GO:0005929
      label: cilium
  downstream:
  - target: Impaired Ventral Forebrain Midline Patterning
  - target: Defective Rathke Pouch and Anterior Pituitary Organogenesis
  - target: Disrupted Anteroposterior Limb Bud Patterning
  - target: Disrupted First Branchial Arch and Craniofacial Patterning
  - target: Reduced Developmental Buffering of the Hedgehog Pathway
  evidence:
  - reference: PMID:27585885
    reference_title: "Gli2 gene-environment interactions contribute to the etiological complexity of holoprosencephaly: evidence from a mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      This genetic predisposition is associated with a Gli2 dosage-dependent
      attenuation of Hedgehog ligand responsiveness at the cellular level.
    explanation: >-
      Directly demonstrates that Gli2 gene dosage sets the magnitude of cellular
      Hedgehog responsiveness, the central effector step of this disease.
  - reference: PMID:22967285
    reference_title: "Relatively high frequency of non-synonymous GLI2 variants in patients with congenital hypopituitarism without holoprosencephaly."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      GLI2 is a downstream transcription factor in Sonic Hedgehog signalling,
      acting early in ventral forebrain and pituitary development.
    explanation: >-
      Locates GLI2 in the Hedgehog cascade and names the two tissues whose
      development is most dependent on it.

- name: Impaired Ventral Forebrain Midline Patterning
  biological_scale: TISSUE
  role: consequence
  description: >-
    Hedgehog signalling from the prechordal plate ventralizes the rostral
    neuroepithelium and drives the midline separation of the eye field and
    prosencephalon. Reduced GLI2-dependent output impairs this midline induction.
    In the mouse, complete Gli2 loss abolishes the floor plate and, on a permissive
    genetic background, reproduces the medial forebrain deficiency and midfacial
    hypoplasia of severe human holoprosencephaly; in humans the heterozygous state
    usually leaves cleavage intact and manifests only as midfacial hypoplasia and
    hypotelorism.
  biological_processes:
  - preferred_term: telencephalon regionalization
    term:
      id: GO:0021978
      label: telencephalon regionalization
    modifier: ABNORMAL
  - preferred_term: floor plate formation
    term:
      id: GO:0021508
      label: floor plate formation
    modifier: DECREASED
  cell_types:
  - preferred_term: neurecto-epithelial cell
    term:
      id: CL:0000710
      label: neurecto-epithelial cell
  downstream:
  - target: Holoprosencephaly-Spectrum Forebrain and Midfacial Malformation
  evidence:
  - reference: PMID:14581620
    reference_title: "Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The secreted protein Shh acts as a crucial factor that patterns the ventral
      forebrain and is required for the division of the primordial eye field and
      brain into two discrete halves.
    explanation: >-
      States the developmental process that GLI2-dependent Hedgehog output serves
      in the ventral forebrain.
  - reference: PMID:9655799
    reference_title: "Gli2 is required for induction of floor plate and adjacent cells, but not most ventral neurons in the mouse central nervous system."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We have found that the floor plate throughout the midbrain, hindbrain and
      spinal cord does not form in Gli2 homozygotes.
    explanation: >-
      Mouse null data show Gli2 is required for ventral midline (floor plate)
      induction, the CNS-patterning step disrupted in this node.
  - reference: PMID:27585885
    reference_title: "Gli2 gene-environment interactions contribute to the etiological complexity of holoprosencephaly: evidence from a mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      On the C57BL/6J background, homozygous GLI2 loss of function results in the
      characteristic brain and facial features seen in severe human HPE, including
      midfacial hypoplasia, hypotelorism and medial forebrain deficiency with loss
      of ventral neurospecification.
    explanation: >-
      Shows that complete Gli2 loss reproduces the human midline forebrain and face
      phenotype, linking this node to its clinical consequence.

- name: Defective Rathke Pouch and Anterior Pituitary Organogenesis
  biological_scale: TISSUE
  role: consequence
  description: >-
    Hedgehog signalling is required at an early step of pituitary formation, when
    Rathke pouch is induced from the oral ectoderm beneath the ventral
    diencephalon. Reduced GLI2 activator output impairs anterior pituitary
    specification and growth and disturbs the descent/positioning of the posterior
    lobe, producing anterior pituitary hypoplasia with an ectopic posterior
    pituitary and interrupted stalk. Gli2 mutant mice have hypoplastic anterior and
    absent posterior pituitary glands, and in zebrafish loss of Gli-mediated
    signalling causes the adenohypophyseal anlage to transdifferentiate into lens.
  biological_processes:
  - preferred_term: pituitary gland development
    term:
      id: GO:0021983
      label: pituitary gland development
    modifier: ABNORMAL
  cell_types:
  - preferred_term: somatotroph
    term:
      id: CL:0002312
      label: somatotroph
  downstream:
  - target: Combined Pituitary Hormone Deficiency
  evidence:
  - reference: PMID:14581620
    reference_title: "Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Our data support a growing body of evidence that Shh signaling is necessary
      for an early step in pituitary formation
    explanation: >-
      Places the GLI2-dependent requirement at an early step of pituitary
      organogenesis.
  - reference: PMID:25878059
    reference_title: "Role of GLI2 in hypopituitarism phenotype."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Gli2 mutant mice have hypoplastic anterior and absent posterior pituitary
      glands.
    explanation: >-
      Mouse data directly demonstrate that Gli2 loss disrupts development of both
      pituitary lobes.
  - reference: PMID:10960781
    reference_title: "Zebrafish mutations in Gli-mediated hedgehog signaling lead to lens transdifferentiation from the adenohypophysis anlage."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The observation argues that overall inhibition of Shh-Gli signaling leads
      the adenohypophysis anlage to transdifferentiate into lens.
    explanation: >-
      Zebrafish gli2 (you-too) mutants show that Shh-Gli signalling maintains
      adenohypophyseal identity; its loss redirects the pituitary primordium to a
      lens fate.
  - reference: PMID:14581620
    reference_title: "Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It is the pituitary and facial structures that are the most sensitive to a
      reduction in GLI2 activity.
    explanation: >-
      Identifies the pituitary as the tissue most sensitive to reduced GLI2 dose in
      humans, explaining why hypopituitarism dominates the phenotype.

- name: Disrupted Anteroposterior Limb Bud Patterning
  biological_scale: TISSUE
  role: consequence
  conforms_to: "limb_digit_patterning_serial_homology#Disrupted Digit Number and Identity Specification"
  description: >-
    Hedgehog signalling from the zone of polarizing activity, read out through the
    GLI transcription factors, specifies digit number and identity along the
    anteroposterior axis of the limb bud. Reduced GLI2 activator dose perturbs this
    readout and produces an extra postaxial digit. This is the most prevalent
    manifestation of a pathogenic GLI2 variant and the mildest expression of the
    condition - frequently the only finding in a transmitting parent.
  biological_processes:
  - preferred_term: limb morphogenesis
    term:
      id: GO:0035108
      label: limb morphogenesis
    modifier: ABNORMAL
  - preferred_term: smoothened signaling pathway
    term:
      id: GO:0007224
      label: smoothened signaling pathway
    modifier: DECREASED
  downstream:
  - target: Postaxial Polydactyly
  notes: >-
    Conformance is declared at the digit-number/identity node rather than the
    module's serially homologous autopod node: GLI2-related polydactyly is
    consistently reported as postaxial and is often unilateral, and the published
    series do not systematically document the hand-plus-foot bundle that the
    serial-homology node asserts.
  evidence:
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most prevalent phenotypic feature is post-axial polydactyly (65%) which
      is also the mildest phenotypic expression of the condition, reported in many
      parents of individuals with systemic findings.
    explanation: >-
      Establishes postaxial polydactyly as the most frequent and mildest expression
      of a pathogenic GLI2 variant.
  - reference: PMID:31782289
    reference_title: "Ectopic Posterior Pituitary, Polydactyly, Midfacial Hypoplasia and Multiple Pituitary Hormone Deficiency due to a Novel Heterozygous IVS11-2A>C(c.1957-2A>C) Mutation in the GLI2 Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      His father and a six-year-old brother with the identical mutation also had
      unilateral postaxial polydactyly and mid-facial hypoplasia although there was
      no pituitary hormone deficiency.
    explanation: >-
      Shows postaxial polydactyly occurring as the isolated manifestation in
      relatives carrying the identical GLI2 splice variant.

- name: Disrupted First Branchial Arch and Craniofacial Patterning
  biological_scale: TISSUE
  role: consequence
  description: >-
    Beyond the midline, reduced Hedgehog output perturbs patterning of the first
    branchial arch and its derivatives and of the developing palate and orbit,
    producing midface hypoplasia, orofacial clefting, temporomandibular joint
    anomalies, and - at the severe end - orbital anomalies with anophthalmia or
    microphthalmia and heminasal aplasia.
  biological_processes:
  - preferred_term: roof of mouth development
    term:
      id: GO:0060021
      label: roof of mouth development
    modifier: ABNORMAL
  downstream:
  - target: Holoprosencephaly-Spectrum Forebrain and Midfacial Malformation
  evidence:
  - reference: PMID:21204792
    reference_title: "Clinical findings in patients with GLI2 mutations--phenotypic variability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Subsequently, anophthalmia plus orbital anomalies, heminasal aplasia,
      branchial arch anomalies and polydactyly have also been incorporated into the
      general phenotype.
    explanation: >-
      Documents branchial arch and orbital anomalies as part of the GLI2 phenotype.
  - reference: PMID:21204792
    reference_title: "Clinical findings in patients with GLI2 mutations--phenotypic variability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Novel sequence variants were found in the GLI2 gene in patients with marked
      involvement of the temporomandibular joint (TMJ), a new clinical finding
      observed with mutations of this gene.
    explanation: >-
      Adds temporomandibular joint involvement, a first-arch derivative, to the
      craniofacial arm of the phenotype.

- name: Reduced Developmental Buffering of the Hedgehog Pathway
  biological_scale: ORGANISM
  role: modifier
  mechanism_confidence: HYPOTHETICAL
  description: >-
    A single functional GLI2 allele is usually sufficient for normal development,
    which is why so many carriers are unaffected. What haploinsufficiency removes
    is reserve: the pathway becomes dose-limited and therefore vulnerable to a
    second genetic or environmental hit during the first-trimester patterning
    window. Mice heterozygous for a Gli2 null allele are indistinguishable from
    wild-type littermates at baseline but show markedly increased penetrance and
    severity of holoprosencephaly after low-dose teratogen or ethanol exposure.
    This provides the mechanistic account of the incomplete penetrance that defines
    the human disorder, but the specific human second hits remain unidentified.
  downstream:
  - target: Holoprosencephaly-Spectrum Forebrain and Midfacial Malformation
  evidence:
  - reference: PMID:27585885
    reference_title: "Gli2 gene-environment interactions contribute to the etiological complexity of holoprosencephaly: evidence from a mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Although normally indistinguishable from wild-type littermates, we
      demonstrate that mice with single-allele Gli2 mutations exhibit increased
      penetrance and severity of HPE in response to low-dose teratogen exposure.
    explanation: >-
      The defining gene-environment experiment: Gli2 heterozygosity is silent alone
      but converts a subthreshold teratogen exposure into holoprosencephaly.
  - reference: PMID:24586787
    reference_title: "The teratogenic effects of prenatal ethanol exposure are exacerbated by Sonic Hedgehog or GLI2 haploinsufficiency in the mouse."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      While Shh(+/-) and Gli2(+/-) mice have been described as phenotypically
      normal, these results illustrate a functional haploinsufficiency of both
      genes in combination with ethanol exposure.
    explanation: >-
      Independent replication with prenatal ethanol as the second hit, supporting
      the reduced-buffering model.
  - reference: PMID:22106008
    reference_title: "A patient with a mild holoprosencephaly spectrum phenotype and heterotaxy and a 1.3 Mb deletion encompassing GLI2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Consistent with prior reports, we observed incomplete penetrance of the
      deletion in the family, illustrating the multifactorial etiology of
      holoprosencephaly spectrum features.
    explanation: >-
      Human family data showing the same incomplete penetrance the mouse model
      explains.

- name: Combined Pituitary Hormone Deficiency
  biological_scale: ORGANISM
  role: outcome
  description: >-
    Structural anterior pituitary failure translates into deficiency of one or more
    anterior pituitary hormones - most often growth hormone, frequently combined
    with TSH, ACTH, prolactin and gonadotropin deficiency, and occasionally with
    antidiuretic hormone deficiency (diabetes insipidus) when the posterior lobe
    axis is involved. Clinically this presents as neonatal hypoglycaemia and
    cholestasis, micropenis and cryptorchidism in male infants, and growth failure
    in childhood.
  biological_processes:
  - preferred_term: growth hormone secretion
    term:
      id: GO:0030252
      label: growth hormone secretion
    modifier: DECREASED
  evidence:
  - reference: PMID:20685856
    reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The index case of family 1 had polydactyly, hypoglycemia, and seizures, and
      GH, TSH, prolactin, ACTH, LH, and FSH deficiencies.
    explanation: >-
      Illustrates the multi-axis anterior pituitary hormone deficiency produced by
      a truncating GLI2 variant.
  - reference: PMID:39938560
    reference_title: "Phenotype and genotype of 23 patients with hypopituitarism and pathogenic GLI2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most patients with a GLI2 variant (21/23, 91%) had hypopituitarism, including
      21.7% (5/23) presenting isolated growth hormone deficiency.
    explanation: >-
      Quantifies the hormonal phenotype in the largest cohort of pathogenic GLI2
      variants, including the isolated-GH-deficiency subset.

- name: Holoprosencephaly-Spectrum Forebrain and Midfacial Malformation
  biological_scale: ORGANISM
  role: outcome
  description: >-
    The structural end-point of impaired midline patterning: most commonly subtle
    midface hypoplasia, hypotelorism, orofacial clefting and a solitary median
    maxillary central incisor, and less commonly overt lobar or semilobar
    holoprosencephaly. The severity of the brain malformation is the dominant
    determinant of neurodevelopmental outcome.
  evidence:
  - reference: PMID:24744436
    reference_title: "Pathogenic mutations in GLI2 cause a specific phenotype that is distinct from holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A common facial phenotype was seen in individuals (with midface hypoplasia,
      cleft lip/palate and hypotelorism) with truncating mutations.
    explanation: >-
      Defines the recurrent midline facial gestalt of GLI2 truncating variants.
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      HPE (6%) or other brain structure abnormalities (15%)
    explanation: >-
      Quantifies how much of the GLI2 morbidity spectrum is structural brain
      malformation.

- name: Postaxial Polydactyly
  biological_scale: ORGANISM
  role: outcome
  description: >-
    An extra digit on the ulnar or fibular side of the hand or foot, unilateral or
    bilateral. It is the single most frequent finding in GLI2 variant carriers and
    is often the only clue that an apparently unaffected parent is a carrier.
  evidence:
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most prevalent phenotypic feature is post-axial polydactyly (65%)
    explanation: >-
      Postaxial polydactyly is the most prevalent manifestation across 60
      individuals with pathogenic GLI2 variants.

mechanistic_hypotheses:
- hypothesis_group_id: gli2_haploinsufficiency
  hypothesis_label: Simple haploinsufficiency of the GLI2 activator
  status: CANONICAL
  description: >-
    The dominant model: pathogenic alleles are functionally null, the wild-type
    allele is unaffected, and disease results from a halved dose of GLI2 activator.
    Supported by the absence of dominant-negative activity in the original
    functional assays and by the fact that whole-gene deletions reproduce the
    phenotype.
  evidence:
  - reference: PMID:14581620
    reference_title: "Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      None of the mutant alleles manifested dominant negative activity in these
      studies.
    explanation: >-
      No dominant-negative activity was demonstrable for any patient allele,
      favouring haploinsufficiency.
  - reference: PMID:22106008
    reference_title: "A patient with a mild holoprosencephaly spectrum phenotype and heterotaxy and a 1.3 Mb deletion encompassing GLI2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our findings confirm the association of haploinsufficiency of GLI2 and mild
      HPE spectrum features.
    explanation: >-
      Whole-gene deletion phenocopies intragenic truncating variants, the classic
      argument for haploinsufficiency.
- hypothesis_group_id: gli2_dominant_negative
  hypothesis_label: Allele-specific dominant-negative interference by truncated GLI2
  status: ALTERNATIVE
  description: >-
    An alternative, probably allele-restricted mechanism in which a truncated GLI2
    protein retaining the N-terminal repressor domain actively interferes with
    Hedgehog signalling rather than simply being inert. Reported for the C-terminal
    frameshift p.P1167LfsX52 in a Culler-Jones family, but not demonstrated for the
    alleles tested in the founding functional study.
  evidence:
  - reference: PMID:30629636
    reference_title: "A novel truncating variant of GLI2 associated with Culler-Jones syndrome impairs Hedgehog signalling."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Functional assays confirmed the pathogenicity of the identified variant and
      revealed a dominant-negative effect of mutant GLI2 on Hedgehog signalling.
    explanation: >-
      Cell-based assays show a dominant-negative effect for this specific
      truncating allele.
- hypothesis_group_id: gli2_second_hit
  hypothesis_label: Gene-environment second hit determines penetrance
  status: EMERGING
  description: >-
    Penetrance and severity are set not by the GLI2 allele alone but by whether a
    second genetic or environmental insult perturbs the already dose-limited
    Hedgehog pathway during the first-trimester patterning window. Strong support in
    the mouse; in humans the specific modifiers remain unidentified, and a possible
    digenic GLI2/HESX1 family has been reported.
  evidence:
  - reference: PMID:27585885
    reference_title: "Gli2 gene-environment interactions contribute to the etiological complexity of holoprosencephaly: evidence from a mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Here, we demonstrate that mutations in Gli2, which encodes a Hedgehog pathway
      transcription factor, can cause or predispose to HPE depending upon gene
      dosage.
    explanation: >-
      Frames Gli2 lesions as either causal or predisposing depending on dosage and
      additional exposure.
  - reference: PMID:39938560
    reference_title: "Phenotype and genotype of 23 patients with hypopituitarism and pathogenic GLI2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A possible digenic origin (GLI2/HESX1) is proposed in one family.
    explanation: >-
      A single reported family suggests a human second-locus contribution; marked
      PARTIAL because it is a proposal in one family, not established digenic
      inheritance.

phenotypes:
- category: Endocrine
  name: Hypopituitarism
  frequency: FREQUENT
  description: >-
    Deficiency of one or more anterior pituitary hormones, ranging from isolated
    growth hormone deficiency to panhypopituitarism. This is the leading reason
    individuals with pathogenic GLI2 variants come to medical attention.
  phenotype_term:
    preferred_term: Hypopituitarism
    term:
      id: HP:0040075
      label: Hypopituitarism
  evidence:
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We analyze the phenotypic descriptions of 60 individuals with pathogenic GLI2
      variants and evidence a morbidity spectrum that includes hypopituitarism
      (58%)
    explanation: >-
      Hypopituitarism in 58% of 60 individuals with pathogenic GLI2 variants maps to
      FREQUENT (30-79%).
  - reference: PMID:39938560
    reference_title: "Phenotype and genotype of 23 patients with hypopituitarism and pathogenic GLI2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most patients with a GLI2 variant (21/23, 91%) had hypopituitarism
    explanation: >-
      An endocrine-ascertained cohort reports a much higher figure (91%); the
      FREQUENT band follows the less ascertainment-biased Corder series.

- category: Endocrine
  name: Growth hormone deficiency
  frequency: FREQUENT
  description: >-
    Central (secondary) growth hormone deficiency, the most consistently reported
    single hormone deficit, presenting as postnatal growth failure and sometimes as
    neonatal hypoglycaemia. It may be isolated or part of a combined deficiency.
  phenotype_term:
    preferred_term: Secondary growth hormone deficiency
    term:
      id: HP:0008240
      label: Secondary growth hormone deficiency
  evidence:
  - reference: PMID:25878059
    reference_title: "Role of GLI2 in hypopituitarism phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Twenty-five patients (16 families) had heterozygous truncating mutations, and
      the phenotype frequently included GH deficiency, a small anterior pituitary
      lobe and an ectopic/undescended posterior pituitary lobe on magnetic
      resonance imaging and postaxial polydactyly.
    explanation: >-
      GH deficiency is described as a frequent component of the truncating-variant
      phenotype across 25 patients in 16 families.

- category: Endocrine
  name: Panhypopituitarism
  description: >-
    Deficiency of all anterior pituitary hormone axes, described from the founding
    report onwards as a primary feature of the GLI2 phenotype in the more severely
    affected individuals.
  phenotype_term:
    preferred_term: Panhypopituitarism
    term:
      id: HP:0000871
      label: Panhypopituitarism
  evidence:
  - reference: PMID:14581620
    reference_title: "Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      whose primary features include defective anterior pituitary formation and
      pan-hypopituitarism
    explanation: >-
      Panhypopituitarism is named as a primary feature of GLI2 loss-of-function
      disease.

- category: Endocrine
  name: Diabetes insipidus
  frequency: OCCASIONAL
  description: >-
    Central diabetes insipidus from antidiuretic hormone deficiency, reported in a
    subset of patients and reflecting posterior as well as anterior pituitary axis
    involvement.
  phenotype_term:
    preferred_term: Diabetes insipidus
    term:
      id: HP:0000873
      label: Diabetes insipidus
  evidence:
  - reference: PMID:20685856
    reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These phenotypes support partial penetrance, variable polydactyly, midline
      facial defects, and pituitary hormone deficiencies, including diabetes
      insipidus, conferred by heterozygous frameshift or nonsense GLI2 mutations.
    explanation: >-
      Diabetes insipidus is explicitly included in the hormone-deficiency spectrum
      of truncating GLI2 variants.
  - reference: PMID:22967285
    reference_title: "Relatively high frequency of non-synonymous GLI2 variants in patients with congenital hypopituitarism without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Two patients had additional diabetes insipidus, indicating deficiencies of
      anterior and posterior pituitary lobes.
    explanation: >-
      Two of the 24 GLI2-variant patients in this cohort had diabetes insipidus
      (about 8%), which maps to OCCASIONAL (5-29%).

- category: Endocrine
  name: Central hypothyroidism
  description: >-
    TSH deficiency as part of combined pituitary hormone deficiency, requiring
    levothyroxine replacement.
  phenotype_term:
    preferred_term: Central hypothyroidism
    term:
      id: HP:0011787
      label: Central hypothyroidism
  evidence:
  - reference: PMID:20685856
    reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      GH, TSH, prolactin, ACTH, LH, and FSH deficiencies
    explanation: >-
      TSH deficiency is documented as part of the multi-axis deficiency in a GLI2
      proband.

- category: Endocrine
  name: Central adrenal insufficiency
  description: >-
    ACTH deficiency with secondary hypocortisolism - the deficit that carries the
    greatest risk of acute decompensation (adrenal crisis, hypoglycaemia) if
    unrecognised.
  phenotype_term:
    preferred_term: Central adrenal insufficiency
    term:
      id: HP:0011734
      label: Central adrenal insufficiency
  evidence:
  - reference: PMID:20685856
    reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In family 3, a girl had hypoglycemia, seizures, excessive thirst and
      polyuria, and GH, ACTH, TSH, and antidiuretic hormone deficiencies.
    explanation: >-
      Documents ACTH deficiency alongside hypoglycaemia in a GLI2 mutation carrier.

- category: Endocrine
  name: Hypogonadotropic hypogonadism
  description: >-
    LH/FSH deficiency causing micropenis and cryptorchidism in infancy and absent or
    delayed puberty, requiring sex steroid replacement.
  phenotype_term:
    preferred_term: Hypogonadotropic hypogonadism
    term:
      id: HP:0000044
      label: Hypogonadotropic hypogonadism
  evidence:
  - reference: PMID:20685856
    reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      one cousin with GH, TSH, LH, and FSH deficiencies
    explanation: >-
      Gonadotropin deficiency is documented within a GLI2 mutation-positive family.

- category: Skeletal
  name: Postaxial polydactyly
  frequency: FREQUENT
  description: >-
    An extra digit on the ulnar or fibular side of the hand or foot, unilateral or
    bilateral. It is the most prevalent single feature of GLI2-related disease and
    is often the only manifestation in a transmitting parent.
  phenotype_term:
    preferred_term: Postaxial polydactyly
    term:
      id: HP:0100259
      label: Postaxial polydactyly
  evidence:
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most prevalent phenotypic feature is post-axial polydactyly (65%) which
      is also the mildest phenotypic expression of the condition
    explanation: >-
      65% of 60 individuals with pathogenic GLI2 variants maps to FREQUENT (30-79%).
  - reference: PMID:31782289
    reference_title: "Ectopic Posterior Pituitary, Polydactyly, Midfacial Hypoplasia and Multiple Pituitary Hormone Deficiency due to a Novel Heterozygous IVS11-2A>C(c.1957-2A>C) Mutation in the GLI2 Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      He had bilateral postaxial polydactyly, mid-facial hypoplasia, high palatal
      arch, micropenis, and bilateral cryptorchidism.
    explanation: >-
      Case-level documentation of bilateral postaxial polydactyly with the
      characteristic midfacial and genital findings.

- category: Craniofacial
  name: Midface hypoplasia
  frequency: FREQUENT
  description: >-
    Underdevelopment of the midface, part of the recurrent facial gestalt of GLI2
    truncating variants together with hypotelorism and orofacial clefting.
  phenotype_term:
    preferred_term: Midface retrusion
    term:
      id: HP:0011800
      label: Midface retrusion
  evidence:
  - reference: PMID:24744436
    reference_title: "Pathogenic mutations in GLI2 cause a specific phenotype that is distinct from holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A common facial phenotype was seen in individuals (with midface hypoplasia,
      cleft lip/palate and hypotelorism) with truncating mutations.
    explanation: >-
      Midface hypoplasia is part of the common facial phenotype of truncating GLI2
      variants.
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      dysmorphic facial features (35%)
    explanation: >-
      Dysmorphic facial features in 35% of 60 individuals with pathogenic GLI2
      variants maps to FREQUENT (30-79%).

- category: Craniofacial
  name: Hypotelorism
  description: >-
    Reduced interocular distance, the mildest recognised midline (microform)
    manifestation of impaired forebrain and midfacial patterning.
  phenotype_term:
    preferred_term: Hypotelorism
    term:
      id: HP:0000601
      label: Hypotelorism
  evidence:
  - reference: PMID:24744436
    reference_title: "Pathogenic mutations in GLI2 cause a specific phenotype that is distinct from holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      with midface hypoplasia, cleft lip/palate and hypotelorism
    explanation: >-
      Hypotelorism is listed as a component of the recurrent GLI2 facial phenotype.

- category: Craniofacial
  name: Orofacial clefting
  frequency: OCCASIONAL
  description: >-
    Cleft lip and/or cleft palate, sometimes bilateral, occasionally as the
    presenting anomaly together with polydactyly.
  phenotype_term:
    preferred_term: Orofacial cleft
    term:
      id: HP:0000202
      label: Orofacial cleft
  evidence:
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      orofacial clefting (17%)
    explanation: >-
      Orofacial clefting in 17% of 60 individuals with pathogenic GLI2 variants maps
      to OCCASIONAL (5-29%).
  - reference: PMID:22106008
    reference_title: "A patient with a mild holoprosencephaly spectrum phenotype and heterotaxy and a 1.3 Mb deletion encompassing GLI2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      bilateral cleft lip and palate and abnormal pituitary gland formation with
      panhypopituitarism
    explanation: >-
      Case-level documentation of bilateral cleft lip and palate with
      panhypopituitarism in a GLI2 deletion carrier.

- category: Craniofacial
  name: Solitary median maxillary central incisor
  description: >-
    A single centrally positioned upper central incisor - a classic microform of the
    holoprosencephaly spectrum, established as part of the GLI2-related phenotype.
  phenotype_term:
    preferred_term: Solitary median maxillary central incisor
    term:
      id: HP:0006315
      label: Solitary median maxillary central incisor
  evidence:
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a solitary median maxillary central incisor is part of the GLI2-related
      phenotypic variability
    explanation: >-
      Establishes SMMCI within the GLI2 phenotype. No frequency is recorded because
      the source reports no proportion - it adds the finding to the spectrum on the
      basis of isolated observations.

- category: Craniofacial
  name: Branchial arch anomaly
  description: >-
    Anomalies of first branchial arch derivatives, including marked temporomandibular
    joint involvement, incorporated into the GLI2 phenotype after the founding
    reports.
  phenotype_term:
    preferred_term: Branchial anomaly
    term:
      id: HP:0009794
      label: Branchial anomaly
  evidence:
  - reference: PMID:21204792
    reference_title: "Clinical findings in patients with GLI2 mutations--phenotypic variability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      anophthalmia plus orbital anomalies, heminasal aplasia, branchial arch
      anomalies and polydactyly have also been incorporated into the general
      phenotype
    explanation: >-
      Branchial arch anomalies are an established component of the GLI2 phenotype.

- category: Craniofacial
  name: Temporomandibular joint anomaly
  description: >-
    Marked structural involvement of the temporomandibular joint, reported as a
    novel GLI2-associated finding in a Brazilian series of six mutation-positive
    patients.
  phenotype_term:
    preferred_term: Abnormality of the temporomandibular joint
    term:
      id: HP:0010754
      label: Abnormality of the temporomandibular joint
  evidence:
  - reference: PMID:21204792
    reference_title: "Clinical findings in patients with GLI2 mutations--phenotypic variability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Novel sequence variants were found in the GLI2 gene in patients with marked
      involvement of the temporomandibular joint (TMJ), a new clinical finding
      observed with mutations of this gene.
    explanation: >-
      The only report of TMJ involvement in GLI2 disease, from a single six-patient
      series; no frequency is recorded because no proportion is available.

- category: Neurological
  name: Holoprosencephaly
  frequency: OCCASIONAL
  subtype: HPE-spectrum
  description: >-
    Incomplete cleavage of the developing forebrain. This is the feature the disease
    is named for but is present in only a small minority of GLI2 variant carriers,
    most often as the semilobar form.
  phenotype_term:
    preferred_term: Holoprosencephaly
    term:
      id: HP:0001360
      label: Holoprosencephaly
  evidence:
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a morbidity spectrum that includes hypopituitarism (58%), HPE (6%)
    explanation: >-
      HPE in 6% of 60 individuals with pathogenic GLI2 variants maps to OCCASIONAL
      (5-29%).
  - reference: PMID:24744436
    reference_title: "Pathogenic mutations in GLI2 cause a specific phenotype that is distinct from holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      only 1 of 43 had frank HPE
    explanation: >-
      An independent series reports frank HPE in only 1 of 43 truncating-variant
      carriers, confirming its rarity.

- category: Neurological
  name: Semilobar holoprosencephaly
  subtype: HPE-spectrum
  description: >-
    Partial hemispheric separation posteriorly with fused frontal lobes - the form of
    holoprosencephaly documented in GLI2 mutation-positive patients at the severe end
    of the spectrum.
  phenotype_term:
    preferred_term: Semilobar holoprosencephaly
    term:
      id: HP:0002507
      label: Semilobar holoprosencephaly
  evidence:
  - reference: PMID:21204792
    reference_title: "Clinical findings in patients with GLI2 mutations--phenotypic variability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      phenotypic manifestations that range from isolated cleft lip/palate with
      polydactyly, branchial arch anomalies to semi-lobar holoprosencephaly
    explanation: >-
      Semilobar holoprosencephaly is the severe end of the range in this GLI2
      mutation-positive series.

- category: Neurological
  name: Neurocognitive impairment
  frequency: FREQUENT
  description: >-
    Neurodevelopmental and cognitive difficulties, reported in a substantial
    proportion of individuals with pathogenic GLI2 variants. Outcome tracks with
    the presence and severity of structural brain malformation; carriers with the
    isolated pituitary/polydactyly presentation may have entirely normal psychomotor
    development.
  phenotype_term:
    preferred_term: Neurocognitive disorder
    term:
      id: HP:0012759
      label: Neurodevelopmental abnormality
  evidence:
  - reference: PMID:39938560
    reference_title: "Phenotype and genotype of 23 patients with hypopituitarism and pathogenic GLI2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The remaining signs included neurocognitive disorders (38%), hexadactyly
      (27%), cardiac septal defects, and renal/vesical abnormalities.
    explanation: >-
      Neurocognitive disorders in 38% of the cohort maps to FREQUENT (30-79%).
  - reference: PMID:22106008
    reference_title: "A patient with a mild holoprosencephaly spectrum phenotype and heterotaxy and a 1.3 Mb deletion encompassing GLI2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a mild holoprosencephaly spectrum phenotype (bilateral cleft lip and palate
      and abnormal pituitary gland formation with panhypopituitarism) and normal
      psychomotor development
    explanation: >-
      Counter-example showing normal psychomotor development in a GLI2 deletion
      carrier without brain malformation; marked PARTIAL because it qualifies the
      frequency rather than supporting it.

- category: Neurological
  name: Seizures
  description: >-
    Seizures, reported in GLI2 mutation carriers - in the described cases in the
    context of hypoglycaemia from combined pituitary hormone deficiency as well as
    of structural brain involvement.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:20685856
    reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The index case of family 1 had polydactyly, hypoglycemia, and seizures
    explanation: >-
      Documents seizures in a GLI2 mutation-positive proband.

- category: Metabolic
  name: Neonatal hypoglycemia
  description: >-
    Hypoglycaemia in the newborn period, a presenting manifestation of GH and ACTH
    deficiency and one of the earliest clues to the diagnosis.
  phenotype_term:
    preferred_term: Neonatal hypoglycemia
    term:
      id: HP:0001998
      label: Neonatal hypoglycemia
  evidence:
  - reference: PMID:31782289
    reference_title: "Ectopic Posterior Pituitary, Polydactyly, Midfacial Hypoplasia and Multiple Pituitary Hormone Deficiency due to a Novel Heterozygous IVS11-2A>C(c.1957-2A>C) Mutation in the GLI2 Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The index case was a boy who developed cholestasis and hypoglycaemia in the
      neonatal period.
    explanation: >-
      Neonatal hypoglycaemia (with cholestasis) as the presenting feature of GLI2
      multiple pituitary hormone deficiency.

- category: Gastrointestinal
  name: Neonatal cholestasis
  description: >-
    Cholestatic jaundice in the neonatal period, a recognised manifestation of
    congenital hypopituitarism, reported in a GLI2 splice-variant index case.
  phenotype_term:
    preferred_term: Cholestasis
    term:
      id: HP:0001396
      label: Cholestasis
  evidence:
  - reference: PMID:31782289
    reference_title: "Ectopic Posterior Pituitary, Polydactyly, Midfacial Hypoplasia and Multiple Pituitary Hormone Deficiency due to a Novel Heterozygous IVS11-2A>C(c.1957-2A>C) Mutation in the GLI2 Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      developed cholestasis and hypoglycaemia in the neonatal period
    explanation: >-
      Case-level documentation of neonatal cholestasis in GLI2-related
      hypopituitarism.

- category: Growth
  name: Short stature
  frequency: FREQUENT
  description: >-
    Postnatal growth failure secondary to growth hormone deficiency, the usual route
    to endocrine referral in childhood; responsive to growth hormone replacement.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:14581620
    reference_title: "Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Proband in family 2 with extreme midfacial hypoplasia, pseudomedian cleft
      lip, and severe growth retardation.
    explanation: >-
      Documents severe growth failure in a GLI2 mutation-positive proband.
  - reference: PMID:25878059
    reference_title: "Role of GLI2 in hypopituitarism phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the phenotype frequently included GH deficiency
    explanation: >-
      GH deficiency - and hence growth failure - is a frequent component of the
      truncating-variant phenotype, supporting the FREQUENT band.

- category: Genitourinary
  name: Micropenis
  description: >-
    Micropenis in male infants, reflecting gonadotropin deficiency during the
    perinatal testosterone surge.
  phenotype_term:
    preferred_term: Micropenis
    term:
      id: HP:0000054
      label: Micropenis
  evidence:
  - reference: PMID:31782289
    reference_title: "Ectopic Posterior Pituitary, Polydactyly, Midfacial Hypoplasia and Multiple Pituitary Hormone Deficiency due to a Novel Heterozygous IVS11-2A>C(c.1957-2A>C) Mutation in the GLI2 Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      high palatal arch, micropenis, and bilateral cryptorchidism
    explanation: >-
      Documents micropenis in a GLI2 multiple-pituitary-hormone-deficiency index
      case.

- category: Genitourinary
  name: Cryptorchidism
  description: >-
    Undescended testes, a further manifestation of perinatal gonadotropin deficiency.
  phenotype_term:
    preferred_term: Cryptorchidism
    term:
      id: HP:0000028
      label: Cryptorchidism
  evidence:
  - reference: PMID:20685856
    reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In family 2, a boy had cryptorchidism, cleft lip and palate, and GH
      deficiency.
    explanation: >-
      Documents cryptorchidism co-occurring with clefting and GH deficiency in a
      GLI2 family.

- category: Ophthalmologic
  name: Anophthalmia or microphthalmia
  description: >-
    Absent or small eye with orbital anomalies, at the severe end of the GLI2
    craniofacial spectrum and the basis of the alternative disease name
    "holoprosencephaly with microphthalmia and first branchial arch anomalies".
  phenotype_term:
    preferred_term: Anophthalmia
    term:
      id: HP:0000528
      label: Anophthalmia
  evidence:
  - reference: PMID:21204792
    reference_title: "Clinical findings in patients with GLI2 mutations--phenotypic variability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Subsequently, anophthalmia plus orbital anomalies, heminasal aplasia,
      branchial arch anomalies and polydactyly have also been incorporated into the
      general phenotype.
    explanation: >-
      Anophthalmia with orbital anomalies is an established but uncommon part of the
      GLI2 phenotype.

- category: Cardiovascular
  name: Cardiac septal defect
  description: >-
    Septal defects reported among the extrapituitary findings in a large cohort of
    pathogenic GLI2 variant carriers; flagged by the authors as warranting further
    investigation.
  phenotype_term:
    preferred_term: Abnormal cardiac septum morphology
    term:
      id: HP:0001671
      label: Abnormal cardiac septum morphology
  evidence:
  - reference: PMID:39938560
    reference_title: "Phenotype and genotype of 23 patients with hypopituitarism and pathogenic GLI2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In addition to polydactyly and neurocognitive disorders, cardiac and renal
      abnormalities were also frequently observed and should be investigated
      further.
    explanation: >-
      Cardiac abnormalities are reported among the extrapituitary features. The
      source calls them "frequently observed" but gives no proportion for cardiac
      involvement specifically, so no frequency band is recorded.

imaging_findings:
- name: Anterior pituitary hypoplasia
  modality: MRI
  description: >-
    A small anterior pituitary lobe on sagittal MRI, the structural correlate of the
    hormone deficiency.
  phenotype_term:
    preferred_term: Anterior pituitary hypoplasia
    term:
      id: HP:0010627
      label: Anterior pituitary hypoplasia
  diagnostic: true
  evidence:
  - reference: PMID:20685856
    reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Magnetic resonance imaging of four patients with GLI2 mutations and
      hypopituitarism showed a hypoplastic anterior pituitary and an ectopic
      posterior pituitary lobe without HPE.
    explanation: >-
      Direct MRI documentation of anterior pituitary hypoplasia in GLI2 mutation
      carriers.

- name: Ectopic posterior pituitary
  modality: MRI
  description: >-
    An undescended posterior pituitary bright spot at or near the median eminence
    rather than in the sella - together with a hypoplastic anterior lobe and absent
    stalk this constitutes the pituitary stalk interruption pattern that is highly
    characteristic of GLI2-related hypopituitarism.
  phenotype_term:
    preferred_term: Ectopic posterior pituitary
    term:
      id: HP:0011755
      label: Ectopic posterior pituitary
  diagnostic: true
  evidence:
  - reference: PMID:22967285
    reference_title: "Relatively high frequency of non-synonymous GLI2 variants in patients with congenital hypopituitarism without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The posterior pituitary lobe on MRI was ectopic in 16, not visible in 4,
      normally placed in 2 and imaging was not available in two patients, but there
      were no signs of holoprosencephaly.
    explanation: >-
      In a GLI2-variant hypopituitarism series the posterior lobe was ectopic in the
      large majority, with no holoprosencephaly.
  - reference: PMID:39938560
    reference_title: "Phenotype and genotype of 23 patients with hypopituitarism and pathogenic GLI2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pituitary morphological abnormalities were present in 84% of the patients with
      P GLI2 variants
    explanation: >-
      Quantifies how consistently structural pituitary abnormality accompanies a
      pathogenic GLI2 variant.

- name: Interrupted pituitary stalk
  modality: MRI
  description: >-
    Absent or interrupted pituitary stalk, completing the pituitary stalk
    interruption syndrome pattern, characteristically without any other midline
    structural abnormality.
  phenotype_term:
    preferred_term: Interrupted pituitary stalk
    term:
      id: HP:0034978
      label: Interrupted pituitary stalk
  evidence:
  - reference: PMID:31782289
    reference_title: "Ectopic Posterior Pituitary, Polydactyly, Midfacial Hypoplasia and Multiple Pituitary Hormone Deficiency due to a Novel Heterozygous IVS11-2A>C(c.1957-2A>C) Mutation in the GLI2 Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      There was severe anterior pituitary hypoplasia, absent pituitary stalk and
      ectopic posterior pituitary on magnetic resonance imaging which suggested
      pituitary stalk interruption syndrome with no other midline structural
      abnormality.
    explanation: >-
      Documents the full stalk-interruption triad in a GLI2 splice-variant carrier.

prevalence:
- population: Worldwide (holoprosencephaly, all causes)
  measure_type: BIRTH_PREVALENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 3.2
  rate_low: 2.6
  rate_high: 3.8
  notes: >-
    Context figure for holoprosencephaly as a whole, not for HPE9. Japanese
    nationwide survey estimate of 0.32 per 10,000 live births (95% CI 0.26-0.38),
    equivalent to 3.2 per 100,000; international estimates for HPE overall span
    0.10-6.06 per 10,000 births.
  evidence:
  - reference: PMID:31886593
    reference_title: "Nationwide epidemiological survey of holoprosencephaly in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the estimated BPR of HPE was calculated to be 0.32 per 10 000 live births
      (95% CI: 0.26-0.38)
    explanation: >-
      Nationwide Japanese birth-prevalence estimate for holoprosencephaly overall.
  - reference: PMID:31886593
    reference_title: "Nationwide epidemiological survey of holoprosencephaly in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Holoprosencephaly (HPE) is a congenital malformation with an estimated
      prevalence of 0.10-6.06 per 10 000 births
    explanation: >-
      Gives the international range of reported HPE birth prevalence.
- population: Worldwide (GLI2-related disease, HPE9)
  measure_type: UNKNOWN
  prevalence_class: NOT_YET_DOCUMENTED
  notes: >-
    No prevalence estimate specific to GLI2-related disease has been published.
    GLI2 contributes a small share of classic holoprosencephaly but is heavily
    enriched among individuals ascertained for syndromic congenital
    hypopituitarism, where it is the most frequently identified genetic cause - so
    population prevalence and diagnostic yield diverge sharply depending on the
    ascertainment route.
  evidence:
  - reference: PMID:39938560
    reference_title: "Phenotype and genotype of 23 patients with hypopituitarism and pathogenic GLI2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      GLI2 variants were the most frequently identified genetic cause in patients
      with syndromic hypopituitarism (68%)
    explanation: >-
      Documents the high diagnostic yield of GLI2 in the syndromic-hypopituitarism
      ascertainment route, in contrast to its minor share of classic HPE.

diagnosis:
- name: Pituitary MRI
  description: >-
    Dedicated sellar/pituitary MRI is the key structural investigation, looking for
    the anterior pituitary hypoplasia, ectopic posterior lobe and absent stalk that
    characterise GLI2-related hypopituitarism, and for any coexisting
    holoprosencephaly-spectrum forebrain malformation.
  evidence:
  - reference: PMID:20685856
    reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Magnetic resonance imaging of four patients with GLI2 mutations and
      hypopituitarism showed a hypoplastic anterior pituitary and an ectopic
      posterior pituitary lobe without HPE.
    explanation: >-
      Establishes the MRI pattern that should prompt GLI2 testing.
- name: Anterior pituitary hormone assessment
  description: >-
    Baseline and dynamic endocrine testing across the GH, ACTH-cortisol,
    TSH-thyroxine, gonadotropin and prolactin axes, plus assessment for diabetes
    insipidus, to define which axes are deficient and guide replacement.
  evidence:
  - reference: PMID:20685856
    reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      GH, TSH, prolactin, ACTH, LH, and FSH deficiencies
    explanation: >-
      The multi-axis deficiency pattern that hormone assessment is designed to
      detect.
- name: GLI2 molecular testing
  description: >-
    Sequencing of GLI2, usually within a holoprosencephaly or congenital
    hypopituitarism gene panel or by exome sequencing, with chromosomal microarray
    when a 2q14.2 deletion is suspected. Cascade testing of apparently unaffected
    relatives is informative because of the marked non-penetrance. Interpretation
    must account for the reclassification of most previously reported GLI2 missense
    variants as benign or low risk.
  evidence:
  - reference: PMID:29771000
    reference_title: "Molecular testing in holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Traditionally, the genetic workup for HPE has been a karyotype, chromosomal
      microarray, and/or Sanger sequencing of select genes.
    explanation: >-
      Describes the molecular testing framework for holoprosencephaly within which
      GLI2 testing sits.
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We show that most of the 31 missense variants previously reported as
      pathogenic are likely benign or, at most, low-risk variants.
    explanation: >-
      Directly informs variant interpretation: most historically reported GLI2
      missense variants should not be called pathogenic.
- name: Chromosomal microarray
  description: >-
    Copy-number analysis, indicated when a contiguous 2q14.2 deletion is suspected -
    the structural-variant counterpart of the 2q14.2 deletion class in the genetic
    section. Sequencing alone will miss a whole-gene deletion, and the deletion
    phenotype is continuous with that of intragenic truncating variants, so a
    negative GLI2 sequencing result does not exclude GLI2 as the cause.
  evidence:
  - reference: PMID:29771000
    reference_title: "Molecular testing in holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Traditionally, the genetic workup for HPE has been a karyotype, chromosomal
      microarray, and/or Sanger sequencing of select genes.
    explanation: >-
      Places chromosomal microarray in the standard holoprosencephaly genetic
      workup alongside sequencing.
  - reference: PMID:22106008
    reference_title: "A patient with a mild holoprosencephaly spectrum phenotype and heterotaxy and a 1.3 Mb deletion encompassing GLI2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Large, microscopically visible, interstitial deletions spanning 2q14.2 have
      been reported in patients with multiple congenital anomalies and intellectual
      disability.
    explanation: >-
      Documents the 2q14.2 deletion class that copy-number analysis is needed to
      detect.

progression:
- notes: >-
    The structural anomalies - forebrain, craniofacial and limb - are fixed at birth
    and do not progress. The endocrine phenotype is congenital in origin but may
    declare itself over time: neonatal hypoglycaemia and cholestasis, then growth
    failure in childhood, then absent or delayed puberty. Hormone deficiencies are
    lifelong and require continuing replacement rather than resolving; the presence
    and severity of structural brain malformation, not the endocrine deficit, is the
    dominant determinant of neurodevelopmental outcome.
  evidence:
  - reference: PMID:31782289
    reference_title: "Ectopic Posterior Pituitary, Polydactyly, Midfacial Hypoplasia and Multiple Pituitary Hormone Deficiency due to a Novel Heterozygous IVS11-2A>C(c.1957-2A>C) Mutation in the GLI2 Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The index case was a boy who developed cholestasis and hypoglycaemia in the
      neonatal period.
    explanation: >-
      Illustrates the neonatal end of the temporal sequence of endocrine
      presentation.
  - reference: PMID:33235745
    reference_title: "A case series of a mother and two daughters with a GLI2 gene deletion demonstrating variable expressivity and incomplete penetrance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sisters 1 and 2 present with the classic dyad of findings in a patient with
      Culler Jones syndrome of growth hormone (GH) deficiency and postaxial
      polydactyly, and their mother also demonstrated postaxial polydactyly at birth
      but otherwise has an unremarkable phenotype.
    explanation: >-
      Shows the childhood presentation (GH deficiency plus polydactyly) alongside a
      lifelong-stable minimal phenotype in the carrier mother.

environmental:
- name: Maternal pregestational diabetes
  influences_mechanisms:
  - target: Reduced Developmental Buffering of the Hedgehog Pathway
    environmental_effect: PREDISPOSES
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This entry models a dose-limited pathway with no reserve, which is the
      substrate on which environmental insults act. Maternal diabetes is the
      best-replicated such insult and raises the chance that a carrier crosses
      into the affected range.
    evidence:
    - reference: PMID:33111505
      reference_title: "Identifying environmental risk factors and gene-environment interactions in holoprosencephaly."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Pregnancy associated risk associated with holoprosencephaly included maternal pregestational diabetes (9.2% of cases and 0 controls, p = .02)"
      explanation: >-
        Reports maternal pregestational diabetes in 9.2% of holoprosencephaly
        cases versus none of the controls, a human association with the
        malformation.
  description: >-
    The most consistently replicated non-genetic risk factor for holoprosencephaly
    in human epidemiology, and therefore the leading candidate second hit for a
    dose-limited GLI2 carrier. The evidence is for holoprosencephaly broadly rather
    than for GLI2 carriers specifically - no study has yet stratified maternal
    diabetes risk by GLI2 genotype, which is precisely what the
    exp_gli2_prospective_periconceptional_exposure_cohort experiment proposes.
  effect: Consistently replicated human risk factor for holoprosencephaly
  evidence:
  - reference: PMID:29761639
    reference_title: "Nongenetic risk factors for holoprosencephaly: An updated review of the epidemiologic literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A 2010 review of the literature identified several risk factors that had been
      consistently identified as occurring more frequently among cases of HPE,
      including maternal diabetes, twinning, and a predominance of females
    explanation: >-
      A CDC systematic review of the epidemiologic literature identifies maternal
      diabetes as one of the risk factors consistently associated with
      holoprosencephaly.
  - reference: PMID:33111505
    reference_title: "Identifying environmental risk factors and gene-environment interactions in holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pregnancy associated risk associated with holoprosencephaly included maternal
      pregestational diabetes (9.2% of cases and 0 controls, p = .02)
    explanation: >-
      A case-control study quantifies the association: pregestational diabetes in
      9.2% of holoprosencephaly cases versus none of the controls.
- name: Prenatal ethanol exposure
  exposure_term:
    preferred_term: maternal exposure to drinking alcohol
    term:
      id: ECTO:0300001
      label: exposure to drinking alcohol via maternal
  influences_mechanisms:
  - target: Reduced Developmental Buffering of the Hedgehog Pathway
    environmental_effect: EXACERBATES
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Ethanol worsens the phenotype specifically on a Hedgehog-sensitised
      background, which is what this node describes: the same dose produces
      far more dysmorphology when one Shh or Gli2 allele is already lost.
    evidence:
    - reference: PMID:24586787
      reference_title: "The teratogenic effects of prenatal ethanol exposure are exacerbated by Sonic Hedgehog or GLI2 haploinsufficiency in the mouse."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Following ethanol exposure, mean dysmorphology scores were increased by 3.2- and 6.6-fold in Shh(+/-) and Gli2(+/-) groups, respectively, relative to their wildtype littermates."
      explanation: >-
        Ethanol raised dysmorphology scores several-fold in Shh and Gli2
        heterozygotes relative to wild type, demonstrating the
        gene-environment interaction. Support is PARTIAL because the
        demonstration is in mice and has not been shown in human carriers.
  description: >-
    Prenatal alcohol exposure interacts with reduced Gli2 dose in the mouse,
    substantially amplifying craniofacial dysmorphology and producing
    holoprosencephaly-spectrum defects that the exposure alone does not cause. It is
    a candidate second hit for the incomplete penetrance seen in human GLI2 carriers,
    though the interaction has not been demonstrated directly in humans.
  effect: Amplifies craniofacial dysmorphology in Gli2 haploinsufficient mice
  evidence:
  - reference: PMID:24586787
    reference_title: "The teratogenic effects of prenatal ethanol exposure are exacerbated by Sonic Hedgehog or GLI2 haploinsufficiency in the mouse."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Following ethanol exposure, mean dysmorphology scores were increased by 3.2-
      and 6.6-fold in Shh(+/-) and Gli2(+/-) groups, respectively, relative to their
      wildtype littermates.
    explanation: >-
      Quantifies the gene-environment amplification of ethanol teratogenicity by Gli2
      haploinsufficiency in mice.
- name: Teratogen exposure during first-trimester patterning
  exposure_term:
    preferred_term: teratogen exposure
    term:
      id: XCO:0000512
      label: teratogen
  influences_mechanisms:
  - target: Reduced Developmental Buffering of the Hedgehog Pathway
    environmental_effect: EXACERBATES
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Low-dose teratogen exposure that a normal embryo tolerates becomes
      damaging once buffering is lost, increasing both penetrance and
      severity. This is the mechanism by which an unaffected carrier parent
      can have a severely affected child.
    evidence:
    - reference: PMID:27585885
      reference_title: "Gli2 gene-environment interactions contribute to the etiological complexity of holoprosencephaly: evidence from a mouse model."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "mice with single-allele Gli2 mutations exhibit increased penetrance and severity of HPE in response to low-dose teratogen exposure"
      explanation: >-
        Single-allele Gli2 mutant mice showed increased penetrance and
        severity of holoprosencephaly after low-dose teratogen exposure.
        Support is PARTIAL because this is a mouse demonstration rather than
        human data.
  description: >-
    Low-dose exposure to a Hedgehog-pathway-antagonising teratogen converts silent
    Gli2 heterozygosity into overt holoprosencephaly in the mouse, the general form
    of the second-hit model for this disorder.
  effect: Increases penetrance and severity of holoprosencephaly in Gli2 heterozygotes
  evidence:
  - reference: PMID:27585885
    reference_title: "Gli2 gene-environment interactions contribute to the etiological complexity of holoprosencephaly: evidence from a mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      mice with single-allele Gli2 mutations exhibit increased penetrance and
      severity of HPE in response to low-dose teratogen exposure
    explanation: >-
      Establishes low-dose teratogen exposure as the environmental arm of the
      gene-environment interaction.

animal_models:
- species: Mus musculus
  genotype: Gli2 homozygous null
  background: C57BL/6J
  description: >-
    Homozygous Gli2 loss of function on the C57BL/6J background reproduces the brain
    and facial features of severe human holoprosencephaly, including midfacial
    hypoplasia, hypotelorism and medial forebrain deficiency. The same genotype on
    other backgrounds does not, making this the clearest demonstration that genetic
    background modifies holoprosencephaly penetrance.
  evidence:
  - reference: PMID:27585885
    reference_title: "Gli2 gene-environment interactions contribute to the etiological complexity of holoprosencephaly: evidence from a mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      On the C57BL/6J background, homozygous GLI2 loss of function results in the
      characteristic brain and facial features seen in severe human HPE, including
      midfacial hypoplasia, hypotelorism and medial forebrain deficiency with loss
      of ventral neurospecification.
    explanation: >-
      Background-dependent recapitulation of the severe human phenotype.
- species: Mus musculus
  genotype: Gli2 heterozygous null
  description: >-
    The model closest to the human carrier state: phenotypically normal at baseline,
    but with a dosage-dependent attenuation of Hedgehog ligand responsiveness that
    predisposes to holoprosencephaly on teratogen or ethanol challenge.
  evidence:
  - reference: PMID:27585885
    reference_title: "Gli2 gene-environment interactions contribute to the etiological complexity of holoprosencephaly: evidence from a mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Although normally indistinguishable from wild-type littermates, we demonstrate
      that mice with single-allele Gli2 mutations exhibit increased penetrance and
      severity of HPE in response to low-dose teratogen exposure.
    explanation: >-
      Directly models the human situation of a silent heterozygous carrier who can
      nevertheless transmit or manifest disease.
- species: Mus musculus
  genotype: Gli2 homozygous null (CNS floor plate)
  description: >-
    Gli2 null embryos fail to form a floor plate throughout the midbrain, hindbrain
    and spinal cord, and lose the cell populations flanking the floor plate, while
    most ventral neuron classes still form - establishing Gli2 as required
    specifically for ventral midline induction.
  evidence:
  - reference: PMID:9655799
    reference_title: "Gli2 is required for induction of floor plate and adjacent cells, but not most ventral neurons in the mouse central nervous system."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We have found that the floor plate throughout the midbrain, hindbrain and
      spinal cord does not form in Gli2 homozygotes.
    explanation: >-
      Defines the specific ventral-midline requirement for Gli2 in the CNS.
- species: Danio rerio
  genotype: you-too (yot) gli2 mutant
  description: >-
    Zebrafish yot mutants, which carry dominant-negative forms of Gli2, develop a
    lens from the adenohypophyseal anlage, showing that Shh-Gli signalling is
    required to maintain pituitary rather than lens identity in the anterior midline.
  evidence:
  - reference: PMID:10960781
    reference_title: "Zebrafish mutations in Gli-mediated hedgehog signaling lead to lens transdifferentiation from the adenohypophysis anlage."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We show here that the zebrafish midline mutants you-too (yot) and iguana (igu)
      develop lenses from the adenohypophysis anlage.
    explanation: >-
      Model-organism evidence for a Gli2-dependent step in adenohypophyseal fate
      specification.

treatments:
- name: Growth hormone replacement
  description: >-
    Recombinant human growth hormone (somatropin) for the growth hormone deficiency
    that is the most consistent hormonal deficit, restoring growth velocity and final
    height.
  therapeutic_modality: PROTEIN_REPLACEMENT
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: somatropin
      term:
        id: NCIT:C837
        label: Somatropin
  target_phenotypes:
  - preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:36936162
    reference_title: "Case report: A case of Culler-Jones syndrome caused by a novel mutation of GLI2 gene and literature review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Once diagnosed, individualized hormone replacement treatment is required for
      each patient.
    explanation: >-
      Individualised hormone replacement is the management principle for GLI2-related
      (Culler-Jones) disease.

- name: Multi-axis pituitary hormone replacement
  description: >-
    Replacement of the remaining deficient axes as identified - hydrocortisone for
    ACTH deficiency (with stress dosing and adrenal crisis education, the most
    safety-critical element), levothyroxine for central hypothyroidism, desmopressin
    for central diabetes insipidus, and sex steroids at the age of puberty for
    hypogonadotropic hypogonadism.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: hydrocortisone
      term:
        id: CHEBI:17650
        label: cortisol
    - preferred_term: levothyroxine
      term:
        id: CHEBI:18332
        label: L-thyroxine
    - preferred_term: desmopressin
      term:
        id: CHEBI:4450
        label: desmopressin
  target_phenotypes:
  - preferred_term: Hypopituitarism
    term:
      id: HP:0040075
      label: Hypopituitarism
  evidence:
  - reference: PMID:20685856
    reference_title: "Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These phenotypes support partial penetrance, variable polydactyly, midline
      facial defects, and pituitary hormone deficiencies, including diabetes
      insipidus, conferred by heterozygous frameshift or nonsense GLI2 mutations.
    explanation: >-
      Establishes the range of hormone axes - including ADH - that require
      replacement in GLI2-related disease.

- name: Surgical correction of postaxial polydactyly
  description: >-
    Excision or reconstruction of the supernumerary postaxial digit, usually in
    infancy or early childhood, for function and appearance. This is standard
    orthopaedic practice rather than a GLI2-specific intervention.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Orthopedic surgical procedure
    term:
      id: NCIT:C16186
      label: Orthopedic Surgical Procedure
  target_phenotypes:
  - preferred_term: Postaxial polydactyly
    term:
      id: HP:0100259
      label: Postaxial polydactyly
  evidence:
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most prevalent phenotypic feature is post-axial polydactyly (65%)
    explanation: >-
      Establishes the frequency of the anomaly this treatment addresses. Marked
      PARTIAL because the source documents the indication, not the intervention.

- name: Cleft lip and palate repair
  description: >-
    Staged surgical repair of cleft lip and palate along standard craniofacial
    protocols, with speech and feeding support.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Surgical procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  target_phenotypes:
  - preferred_term: Orofacial cleft
    term:
      id: HP:0000202
      label: Orofacial cleft
  evidence:
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      orofacial clefting (17%)
    explanation: >-
      Establishes the frequency of the anomaly this treatment addresses. Marked
      PARTIAL because repair follows generic craniofacial protocols not evaluated in
      this source.

- name: Genetic counselling
  description: >-
    Counselling must address the two facts that make GLI2 unusual: a phenotypically
    normal parent may carry the variant (so a negative family history does not lower
    recurrence risk), and a carrier child's phenotype cannot be predicted from the
    genotype. Cascade testing and the reclassification of most GLI2 missense variants
    as benign are both central to the discussion.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our approach clarifies clinical risks and the important messages to discuss in
      counseling for a pathogenic GLI2 variant.
    explanation: >-
      Frames genotype-informed counselling as the explicit clinical deliverable of
      GLI2 genotype-phenotype analysis.
  - reference: PMID:25878059
    reference_title: "Role of GLI2 in hypopituitarism phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The mutation was frequently inherited from an asymptomatic parent.
    explanation: >-
      The counselling fact that most complicates recurrence-risk discussion.

differential_diagnoses:
- name: SHH-related holoprosencephaly spectrum
  description: >-
    The commonest single-gene cause of holoprosencephaly, likewise autosomal dominant
    with incomplete penetrance, but with frank forebrain non-cleavage and severe
    midline facial anomalies far more prominent, and pituitary deficiency far less
    so, than in GLI2 disease. SHH, ZIC2, SIX3 and TGIF1 are the four major
    holoprosencephaly genes and should be tested alongside GLI2.
  evidence:
  - reference: PMID:21204792
    reference_title: "Clinical findings in patients with GLI2 mutations--phenotypic variability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pathological mutations in holoprosencephaly have been identified in several
      genes that include: SHH, GLI2, PTCH1, TGIF1, ZIC2, SIX3
    explanation: >-
      Names the other holoprosencephaly genes that constitute the genetic
      differential diagnosis for a GLI2 phenotype.
- name: Pallister-Hall syndrome and other GLI3-related disorders
  description: >-
    The other GLI-family developmental disorder: also features polydactyly and
    hypothalamic/pituitary involvement, but with hypothalamic hamartoma, central
    polydactyly patterns, bifid epiglottis and imperforate anus that are not part of
    the GLI2 phenotype.
  evidence:
  - reference: PMID:14581620
    reference_title: "Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Pallister-Hall syndrome, or several distinct polydactyly disorders
    explanation: >-
      Places Pallister-Hall syndrome and the GLI3 polydactyly disorders as the
      sibling GLI-family conditions; evidence source is MODEL_ORGANISM because the
      statement is made about Gli3 null mice recapitulating the human syndromes.
- name: Non-syndromic pituitary stalk interruption syndrome
  description: >-
    The identical MRI triad of anterior pituitary hypoplasia, ectopic posterior lobe
    and absent stalk arises from many causes; the presence of postaxial polydactyly or
    midline facial features is what should redirect testing toward GLI2.
  evidence:
  - reference: PMID:39938560
    reference_title: "Phenotype and genotype of 23 patients with hypopituitarism and pathogenic GLI2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All these GLI2 variants were identified in 23 patients (17 index cases and 6
      relatives) with associated pituitary stalk interruption syndrome or
      extrapituitary manifestations.
    explanation: >-
      Every pathogenic GLI2 variant in this cohort carried either stalk interruption
      or an extrapituitary feature, so an isolated stalk-interruption picture without
      extrapituitary findings points away from GLI2.
- name: Other genetic causes of combined pituitary hormone deficiency
  description: >-
    HESX1, LHX3, LHX4, OTX2, PROP1, POU1F1 and SOX3 among others. GLI2 is
    distinguished by its extrapituitary features - polydactyly above all - and is now
    the most frequently identified cause of the syndromic form.
  evidence:
  - reference: PMID:39938560
    reference_title: "Phenotype and genotype of 23 patients with hypopituitarism and pathogenic GLI2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      GLI2 was the most frequently identified genetic cause of syndromic CH with
      constant association of pituitary stalk interruption syndrome or extrapituitary
      clinical features.
    explanation: >-
      Positions GLI2 relative to the other congenital hypopituitarism genes and names
      the features that distinguish it.
- name: Smith-Lemli-Opitz syndrome
  description: >-
    A cholesterol biosynthesis defect that phenocopies Hedgehog pathway disruption,
    with holoprosencephaly-spectrum midline defects, polydactyly and genital anomalies,
    but is autosomal recessive and biochemically diagnosable by elevated
    7-dehydrocholesterol.
  evidence:
  - reference: PMID:14581620
    reference_title: "Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Pharmacological inhibition of cholesterol synthesis in rats, which inhibits Hh
      signaling, can cause HPE-like findings including alterations in pituitary
      formation
    explanation: >-
      Establishes the mechanistic basis for the phenocopy - blocking cholesterol
      synthesis inhibits Hedgehog signalling and reproduces HPE-like pituitary
      findings. Marked PARTIAL because the rat experiment models the pathway overlap
      rather than documenting Smith-Lemli-Opitz syndrome itself.

discussions:
- discussion_id: hpe9_nomenclature
  kind: CONTROVERSY
  prompt: >-
    Is "holoprosencephaly 9" the right name for a disorder in which frank
    holoprosencephaly occurs in roughly 6% of carriers?
  status: OPEN
  attaches_to:
  - "pathophysiology#Holoprosencephaly-Spectrum Forebrain and Midfacial Malformation"
  rationale: >-
    The HPE9 designation predates the large genotype-phenotype series and reflects
    the ascertainment of the original cohorts, which were screened for
    holoprosencephaly. Subsequent series consistently show that pituitary anomalies
    and postaxial polydactyly, not forebrain non-cleavage, are the modal
    presentation, which is why the milder presentation was split out as Culler-Jones
    syndrome. dismech keeps a single entry under the MONDO label holoprosencephaly 9
    with the two presentations modelled as subtypes, but the naming remains a live
    question and a curator considering a separate Culler-Jones entry should read this
    note first.
  evidence:
  - reference: PMID:24744436
    reference_title: "Pathogenic mutations in GLI2 cause a specific phenotype that is distinct from holoprosencephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Individuals with truncating mutations in GLI2 typically present with pituitary
      anomalies, polydactyly and subtle facial features rather than HPE.
    explanation: >-
      The finding that motivates the nomenclature question.

- discussion_id: gli2_penetrance_modifiers
  kind: KNOWLEDGE_GAP
  prompt: >-
    What determines whether a human GLI2 loss-of-function carrier is unaffected, has
    isolated polydactyly, or has hypopituitarism with holoprosencephaly?
  status: OPEN
  attaches_to:
  - "pathophysiology#Reduced Developmental Buffering of the Hedgehog Pathway"
  rationale: >-
    The mouse work establishes that a second hit converts silent Gli2 heterozygosity
    into overt disease, but the human modifiers are unknown. No modifier locus has
    been validated, only a single family with a proposed digenic GLI2/HESX1
    contribution, and no human study has tested the teratogen interaction directly.
    Identifying the modifiers would convert an unpredictable counselling situation
    into a stratifiable one.
  proposed_experiments:
  - experiment_id: exp_gli2_modifier_sequencing_discordant_relatives
    name: Modifier sequencing in phenotypically discordant carrier relatives
    description: >-
      Sequence the full Hedgehog pathway and known congenital hypopituitarism genes
      in relatives who share an identical GLI2 allele but differ in phenotype, to
      test for modifier or second-locus alleles. Enrichment of pathway alleles in
      affected relative to unaffected carriers would support an oligogenic
      contribution to penetrance; no enrichment would point instead to stochastic or
      environmental determinants.
  - experiment_id: exp_gli2_prospective_periconceptional_exposure_cohort
    name: Prospective periconceptional exposure cohort of GLI2 carriers
    description: >-
      Assemble a cohort of pregnancies in known GLI2 carrier families with
      prospectively recorded periconceptional exposures (alcohol, maternal diabetes,
      cholesterol biosynthesis inhibitors) and relate exposure to offspring
      phenotype. An exposure-severity gradient would translate the mouse
      gene-environment model into humans; phenotype independent of recorded exposures
      would confine that model to the mouse.
  - experiment_id: exp_gli2_hedgehog_dose_response_patient_fibroblasts
    name: Hedgehog dose-response assay in patient fibroblasts
    description: >-
      Measure Hedgehog ligand dose-response in fibroblasts from GLI2 variant carriers
      spanning the phenotypic range, mirroring the mouse cellular assay. Residual
      pathway output correlating with phenotype severity would make cellular Hedgehog
      responsiveness a candidate predictive biomarker; uniform attenuation across
      phenotypically discordant carriers would exclude it.
  evidence:
  - reference: PMID:39938560
    reference_title: "Phenotype and genotype of 23 patients with hypopituitarism and pathogenic GLI2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A possible digenic origin (GLI2/HESX1) is proposed in one family.
    explanation: >-
      The only human second-locus lead currently reported; marked PARTIAL because it
      is a single proposed family.

- discussion_id: gli2_mouse_heterozygote_mismatch
  kind: HUMAN_MODEL_MISMATCH
  prompt: >-
    Does the mouse Gli2 heterozygote faithfully model the human GLI2 carrier, given
    that heterozygous mice are phenotypically normal whereas a majority of human
    carriers manifest at least polydactyly?
  status: OPEN
  attaches_to:
  - "pathophysiology#Reduced Developmental Buffering of the Hedgehog Pathway"
  rationale: >-
    The human disorder is dominant with roughly 65% of pathogenic-variant carriers
    showing postaxial polydactyly, whereas Gli2 heterozygous mice are described as
    indistinguishable from wild-type littermates without a second insult, and the
    murine phenotype that does resemble severe human holoprosencephaly requires
    homozygous loss on a permissive background. The species therefore differ in where
    the developmental threshold sits relative to a single functional allele. This
    matters because the second-hit model of human non-penetrance rests largely on
    heterozygous-mouse data; if the human heterozygote is already below threshold in
    the limb, the environmental component may be less necessary for the human
    phenotype than the mouse experiments imply.
  proposed_experiments:
  - experiment_id: exp_gli2_het_mouse_limb_phenotyping_across_backgrounds
    name: Systematic limb phenotyping of Gli2 heterozygous mice across backgrounds
    description: >-
      Score autopod morphology in Gli2 heterozygous mice on several genetic
      backgrounds, since polydactyly may have been under-ascertained in models scored
      primarily for craniofacial dysmorphology. Finding unreported polydactyly would
      reconcile the species; confirmed absence across backgrounds would establish a
      real species difference in developmental threshold.
  - experiment_id: exp_gli2_cross_species_hedgehog_dose_response
    name: Cross-species Hedgehog dose-response comparison
    description: >-
      Compare Hedgehog ligand dose-response curves in mouse Gli2 heterozygous
      fibroblasts and human GLI2-variant patient fibroblasts. Lower residual pathway
      output in human cells would explain why human heterozygotes manifest and mouse
      heterozygotes do not; equivalent curves would locate the difference downstream
      of cellular Hedgehog responsiveness.
  evidence:
  - reference: PMID:27585885
    reference_title: "Gli2 gene-environment interactions contribute to the etiological complexity of holoprosencephaly: evidence from a mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Although normally indistinguishable from wild-type littermates, we demonstrate
      that mice with single-allele Gli2 mutations exhibit increased penetrance and
      severity of HPE in response to low-dose teratogen exposure.
    explanation: >-
      States the mouse heterozygote baseline that differs from the human carrier
      state.
  - reference: PMID:34921505
    reference_title: "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most prevalent phenotypic feature is post-axial polydactyly (65%)
    explanation: >-
      Establishes that most human heterozygotes are not phenotypically silent, unlike
      the mouse.

notes: >-
  Curated from a claude_code deep-research report
  (research/Holoprosencephaly_9-deep-research-claude_code.md) used as a
  lead-generation source only: every PMID, snippet and ontology term in this entry
  was independently verified against the cached abstract or against OAK. Several
  ontology terms suggested by the report were wrong and were replaced (HP:0004926
  and HP:0030082 do not denote panhypopituitarism or holoprosencephaly). Named
  entity confusion preflight passed: MONDO:0012563 names GLI2 (HGNC:4318) as the
  causal gene and cross-references OMIM:610829, matching the gene and OMIM entry
  discussed throughout the source literature. No conformance is declared to
  ciliopathy_dysfunction#Impaired Hedgehog Signal Transduction: GLI2 acts downstream
  of the primary cilium and the lesion here is not a ciliary assembly or trafficking
  defect, so that module's trigger does not apply. GeneReviews has no GLI2-specific
  chapter; the Holoprosencephaly Overview (PMID:20301702) is tagged as the
  GeneReviews baseline, but its PubMed record carries only the chapter's purpose
  statement rather than a Clinical Characteristics section, so phenotype
  cross-referencing was done against the primary cohort literature instead.

📚

References & Deep Research

References

1

PMID:20301702

Holoprosencephaly Overview

No top-level findings curated for this source.

Deep Research

1

Claude Code ▸

Holoprosencephaly 9 (HPE9, GLI2-Related Holoprosencephaly): Comprehensive Research Report

claude-haiku-4-5-20251001, claude-sonnet-5 33 citations 2026-07-30T23:52:36.480911

Holoprosencephaly 9 (HPE9, GLI2-Related Holoprosencephaly): Comprehensive Research Report

1. Disease Information

Overview: Holoprosencephaly 9 (HPE9) is one of the numbered genetic subtypes of holoprosencephaly (HPE), the most common structural malformation of the developing forebrain in humans, caused by heterozygous mutations in GLI2 (GLI-Kruppel family member 2), a zinc-finger transcription factor that mediates Sonic Hedgehog (SHH) signaling. HPE9 is defined by a wide phenotypic spectrum — from frank forebrain non-cleavage (classic HPE) at the severe end, to an entirely distinct, more common presentation of pituitary anomalies, postaxial polydactyly, and subtle midfacial features without any brain cleavage defect at the milder end OMIM #610829; PMID:14581620. Because of this, the field has moved toward viewing GLI2 pathogenic variants as causing a phenotype distinct from classic HPE rather than "true" holoprosencephaly in most patients — GeneReviews notes GLI2 variants more often produce "pituitary anomalies, polydactyly, and subtle facial features (sometimes similar to HPE facial features)" than overt HPE (GeneReviews: Holoprosencephaly Overview, NBK1530). The milder, non-HPE end of the spectrum is now separately cataloged as Culler-Jones syndrome (CJS; OMIM #615849) — postaxial polydactyly–anterior pituitary anomalies–facial dysmorphism syndrome — caused by the same gene.

Key identifiers: - OMIM: #610829 (HPE9, phenotype); 165230 (GLI2, gene) - Related OMIM phenotype: #615849 (Culler-Jones syndrome, allelic disorder) - Gene: GLI2, HGNC:4318, chromosome 2q14.2, NCBI Gene ID 2735/2736 region - MONDO: A MONDO term for "holoprosencephaly 9" exists (indexed by NORD's Mondo-disease pages and ClinVar cross-references) but the exact MONDO CURIE could not be independently confirmed via the search tools used in this session — verify locally with an OAK lookup (e.g., runoak -i sqlite:obo:mondo search "holoprosencephaly 9") before use in curation. - Orphanet: HPE is cataloged generally as ORPHA:2162 (Holoprosencephaly); GLI2-specific HPE9 subtype entries exist in Orphanet's gene-disease association tables. - ICD-10: Q04.2 (Holoprosencephaly, general code; no HPE9-specific ICD-10/11 code exists) - Inheritance database cross-refs:* ClinVar aggregates GLI2 variants under "Holoprosencephaly 9" (e.g., RCV000030728).

Synonyms: HPE9; GLI2-related holoprosencephaly; Holoprosencephaly, GLI2-associated; (allelic, milder disorder) Culler-Jones syndrome; postaxial polydactyly–anterior pituitary anomalies–facial dysmorphism syndrome.

Evidence basis: Information is derived predominantly from aggregated case-series/cohort resources (OMIM, Orphanet, GeneReviews, ClinVar) built from published human case reports and cohort studies (not raw EHR data). The largest primary literature sources are multi-family cohort papers (e.g., Roessler et al. 2003, Bertolacini et al. 2012, Corder et al. 2022) rather than large-scale registries, reflecting HPE9's rarity.

2. Etiology

Disease causal factors — genetic: HPE9 is caused by heterozygous, typically loss-of-function, mutations in GLI2 (chromosome 2q14.2), a primary transcriptional effector of SHH signaling in the developing forebrain, face, and pituitary. Roessler et al. (2003) first established the disease-gene link, reporting "loss-of-function mutations in the human GLI2 gene are associated with a distinctive phenotype (within the HPE spectrum)... characterized by defective anterior pituitary formation and pan-hypopituitarism, with or without overt forebrain cleavage abnormalities, and HPE-like midfacial hypoplasia" PMID:14581620, PNAS 100(23):13424-13429, 2003.

Mutation spectrum includes nonsense, frameshift, splice-site, and missense variants, as well as contiguous gene deletions encompassing GLI2 (e.g., a 1.3 Mb 2q14 deletion producing a mild HPE-spectrum phenotype with heterotaxy, PMID:22106008). Truncating variants that remove the C-terminal transcriptional activator domain are the best-characterized loss-of-function class and are more strongly associated with pituitary anomalies and polydactyly than missense/zinc-finger variants (Corder et al. 2022, AJMG-A, "Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism").

Relative contribution among HPE genes: The four major HPE genes (SHH, ZIC2, SIX3, TGIF1) together account for point mutations/microrearrangements in ~27% of isolated HPE cases (SHH ~12%, ZIC2 ~9%, SIX3 ~5%, TGIF1 ~1%). GLI2 and PTCH1 are "minor" genes, individually contributing <1% of classic HPE, though GLI2 is disproportionately represented among patients ascertained for the pituitary-anomaly/polydactyly phenotype rather than classic HPE — in one screened cohort of ~400 individuals with HPE-spectrum features, roughly 28% carried a GLI2 variant of some kind (most benign/uncertain significance; a minority pathogenic) (Bertolacini et al. 2012, PMID:21204792).

Genetic risk factors: - Heterozygous pathogenic/likely pathogenic GLI2 variants (nonsense, frameshift, splice, deletion; some missense in zinc-finger or activator domains) - De novo occurrence in many probands, but familial transmission with incomplete penetrance is common — a hallmark of GLI2-HPE - No established polygenic/susceptibility-locus modifiers specific to GLI2-HPE beyond the general HPE genetic-modifier literature (e.g., variants in other SHH-pathway genes can act as "second hits" in digenic-like models, per the broader HPE genotype-phenotype literature)

Environmental risk factors (relevant to the broader HPE spectrum, and shown experimentally to interact with Gli2 dosage): - Maternal pregestational diabetes — the single most robust environmental HPE risk factor, conferring >10-fold increased risk, with HPE occurring in ~1–2% of diabetic pregnancies; proposed mechanism involves oxidative stress and disrupted neural crest migration. - Retinoic acid excess — teratogenic in animal models via SHH pathway gene misregulation. - Cholesterol biosynthesis inhibitors (e.g., statins) and metabolic disorders of cholesterol synthesis (Smith-Lemli-Opitz syndrome, DHCR7) — cholesterol is required for SHH ligand post-translational modification and pathway activity. - Maternal alcohol exposure — a mouse study specifically demonstrates Gli2 gene-dosage × ethanol interaction: "The Teratogenic Effects of Prenatal Ethanol Exposure Are Exacerbated by Sonic Hedgehog or Gli2 Haploinsufficiency in the Mouse" (PMC3929747), directly demonstrating a gene-environment interaction relevant to GLI2 haploinsufficiency in humans.

Protective factors: No specific protective genetic or environmental factors for GLI2-HPE are established in the literature reviewed; general HPE literature does not identify protective alleles analogous to those in other Mendelian disorders.

Gene-environment interactions: The mouse Gli2 haploinsufficiency/ethanol model (above) and a separate mouse study on "Gli2 gene-environment interactions contribute to the etiological complexity of holoprosencephaly" (PMID:27585885; PMC5117230) provide the strongest direct mechanistic evidence: mice heterozygous for a Gli2 null allele are phenotypically normal at baseline but show markedly increased penetrance and severity of HPE-spectrum defects when exposed to low-dose teratogens — a model for the incomplete penetrance seen in human GLI2-mutation carriers and consistent with a genetic "second hit"/environmental modifier framework broadly invoked in HPE etiology.

3. Phenotypes

Because most human GLI2 mutation carriers present with the pituitary/polydactyly/facial phenotype rather than classic HPE, the phenotype list below spans that full spectrum, with HPO terms suggested.

Phenotype	Type	Frequency (approx., from cohort data)	Onset	Suggested HPO term
Postaxial polydactyly (hands and/or feet)	Physical/clinical sign	Frequent — reported in ~4/6 in one cohort, and the defining "polydactyly" arm of Culler-Jones syndrome	Congenital	HP:0100259 (Postaxial polydactyly) / HP:0001162
Panhypopituitarism / multiple pituitary hormone deficiency (MPHD)	Endocrine/laboratory	Frequent among GLI2-mutation carriers ascertained via endocrine clinics	Neonatal–childhood	HP:0004926 (Panhypopituitarism)
Growth hormone deficiency	Endocrine	Common component of MPHD	Infancy–childhood	HP:0000824
Ectopic posterior pituitary lobe / pituitary stalk interruption, hypoplastic anterior pituitary	Imaging/structural	Common on MRI in GLI2-hypopituitarism cases, "without HPE"	Congenital	HP:0011750 / HP:0002591 (Hypoplasia of the pituitary gland)
Diabetes insipidus	Endocrine	Reported in a subset	Infancy–childhood	HP:0000873
Midfacial hypoplasia	Craniofacial	Common, part of the shared "truncating-mutation facial phenotype"	Congenital	HP:0000308
Hypotelorism	Craniofacial	Common	Congenital	HP:0000601
Cleft lip/cleft palate	Craniofacial	Present in a substantial minority; ranges to isolated cleft lip/palate + polydactyly as sole presentation	Congenital	HP:0410030 / HP:0000175
First branchial-arch anomalies (mandibular hypoplasia, abnormal/malformed ears, pre-auricular tags)	Craniofacial	Reported, including a "novel" TMJ (temporomandibular joint) anomaly finding	Congenital	HP:0009925 (Abnormal external ear morphology)
Semilobar holoprosencephaly (brain non-cleavage)	Structural CNS	Uncommon among GLI2 carriers — only 1/43 truncating-variant carriers in one review had frank HPE	Prenatal/congenital	HP:0030082 (Holoprosencephaly) / HP:0002573 (Semilobar holoprosencephaly, per HPO hierarchy)
Seizures	Neurological	Reported, part of Culler-Jones syndrome core features	Variable	HP:0001250
Intellectual disability	Neurological/behavioral	Reported, variable severity	Childhood	HP:0001249
Growth impairment / short stature	Systemic	Secondary to GH deficiency	Childhood	HP:0004322
Micropenis, cryptorchidism	Genital	Reported, secondary to hypogonadotropic hypogonadism component of MPHD	Congenital/infancy	HP:0000054, HP:0000028
Hearing loss/deafness (in at least one reported Culler-Jones case)	Sensory	Case-report level	Variable	HP:0000365

Characteristics: - Age of onset: Congenital (structural/craniofacial and polydactyly features present at birth); pituitary hormone deficiencies often manifest neonatally (hypoglycemia, prolonged jaundice) or emerge through childhood as growth failure. - Severity/progression: Highly variable — from isolated cleft lip/palate with polydactyly at the mild end to semilobar HPE at the severe end. Endocrine deficits are typically stable but require lifelong hormone replacement; they are not degenerative. - Frequency among carriers — the defining feature is incomplete penetrance: In one key family study, of 11 parents carrying the same pathogenic GLI2 mutation as an affected proband, "only two had hypopituitarism and three had only polydactyly, while six were apparently completely normal," demonstrating that even severe loss-of-function alleles show markedly incomplete penetrance Roessler et al. 2003; summarized in Journal of Molecular Endocrinology 54(3):R141. - Quality of life impact: Untreated panhypopituitarism carries risk of adrenal crisis, severe hypoglycemia, and growth failure; with hormone replacement, endocrine outcomes are generally good. Craniofacial/limb anomalies may require surgical correction (cleft repair, polydactyly excision). Neurodevelopmental outcome tracks with brain structural involvement — normal-to-mild in isolated pituitary/polydactyly presentations, more impaired when frank HPE or seizures are present (Culler-Jones syndrome cohort).

4. Genetic/Molecular Information

Causal gene: GLI2 (GLI-Kruppel family member 2), OMIM 165230, HGNC:4318, located at chromosome 2q14.2. Human GLI2 protein contains an N-terminal transcriptional repressor domain and a C-terminal transcriptional activator domain; it binds DNA via C2H2 zinc-finger motifs* (ScienceDirect Topics: GLI2; PMID:10433919).

Variant classification and type: - Truncating variants (nonsense, frameshift, splice-site) that eliminate the C-terminal activator domain — the best-established pathogenic class, associated with pituitary anomalies, polydactyly, and the characteristic facial gestalt (midface hypoplasia, cleft lip/palate, hypotelorism) Corder et al. 2022. - Zinc-finger (DNA-binding domain) missense variants — also implicated in hypopituitarism per the same 2022 study title ("Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism"). - Contiguous deletions spanning GLI2 at 2q14 — reported to produce milder HPE-spectrum phenotypes, occasionally with additional features (e.g., heterotaxy) attributable to deletion of neighboring genes PMID:22106008. - Synonymous and other missense variants are frequently identified but often classified benign/VUS — in the Bertolacini et al. 2012 cohort of 110 craniofacial-anomaly patients, 14 GLI2 variants were found (1 deletion, 1 insertion, 9 nonsynonymous, 3 synonymous), with only a subset (6 patients) judged possibly pathogenic PMID:21204792.

Functional consequence: Predominantly loss of function / haploinsufficiency. Roessler et al. functionally demonstrated that identified mutant alleles "lack GLI2 activity," establishing a functional link between GLI2 loss and the human phenotype PMID:14581620.

Somatic vs. germline: All reported HPE9/Culler-Jones variants are germline (constitutional), consistent with a developmental malformation syndrome; GLI2 is separately implicated in somatic oncogenic activation in some cancers (e.g., medulloblastoma, via Hedgehog pathway dysregulation), but that is mechanistically and clinically distinct from HPE9 and outside its scope.

Allele frequency: No population carrier-frequency data specific to pathogenic GLI2 HPE9 alleles were found in gnomAD-level detail in this search; given autosomal dominant inheritance with reduced penetrance and case-level/small-family reporting, pathogenic variants are expected to be very rare/private (population allele frequency approaching zero in large reference databases), consistent with ultra-rare disease status.

Modifier genes: No specific human modifier genes are validated for GLI2-HPE beyond the broader HPE "multiple-hit" model (interaction with other SHH-pathway gene variants, e.g., SHH, PTCH1, ZIC2, in trans, has been proposed in the general HPE genetics literature as contributing to phenotypic variability, though not GLI2-specific confirmed digenic cases in the sources reviewed here).

Epigenetic information: No GLI2-HPE9-specific DNA methylation or chromatin-modification data were identified in this search; GLI2 activity is regulated post-translationally (proteolytic processing/degradation is suppressed by active SHH signaling — PMID: PMC1447407, "Sonic hedgehog Signaling Regulates Gli2 Transcriptional Activity by Suppressing Its Processing and Degradation") rather than primarily by epigenetic mechanisms.

Chromosomal abnormalities: 2q14 microdeletions encompassing GLI2 are a recognized structural-variant cause, producing a phenotype continuous with point-mutation HPE9 (mild HPE-spectrum features, occasionally with contiguous-gene effects) PMID:22106008.

Suggested gene/ontology annotations: HGNC:4318 (GLI2); GO:0007224 (Smoothened signaling pathway); GO:0008589 (regulation of Smoothened signaling pathway); GO:0003700 (DNA-binding transcription factor activity); GO:0008270 (zinc ion binding, for the C2H2 zinc-finger domains).

5. Environmental Information

Environmental factors: No GLI2-HPE9-specific toxin/pollutant exposure data identified; the general HPE environmental risk-factor literature (maternal diabetes, retinoic acid, cholesterol-synthesis-inhibiting drugs, alcohol) is the best proxy, and the mouse Gli2-haploinsufficiency/ethanol interaction study provides direct mechanistic support for gene-dose-dependent teratogen sensitivity relevant to GLI2 carriers specifically PMC3929747.
Lifestyle factors: Maternal glycemic control in pregnancy is the most actionable modifiable factor relevant to the broader HPE spectrum, given the strong maternal-diabetes association.
Infectious agents: None established for HPE or HPE9 specifically.

6. Mechanism / Pathophysiology

Molecular pathway: GLI2 acts as the principal transcriptional effector of the Sonic Hedgehog (SHH) signaling pathway (KEGG hsa04340; GO:0007224) in the ventral forebrain, craniofacial mesenchyme/first branchial arch, limb bud, and developing pituitary (Rathke's pouch). Canonical pathway logic:

Ligand-receptor step: In the absence of SHH ligand, the 12-pass transmembrane receptor PTCH1 inhibits accumulation and activity of SMO (Smoothened) in the primary cilium.
Ligand engagement: SHH binding to PTCH1 relieves this inhibition, allowing SMO to translocate into/accumulate within the primary cilium (a step also dependent on membrane cholesterol, which both modifies the SHH ligand post-translationally and licenses SMO activation) ScienceDirect: Patched, Smoothened and cholesterol.
GLI2 liberation: Active ciliary SMO drives dissociation of the SUFU–GLI2 repressive complex (with assistance from EVC/EVC2 at the ciliary base), releasing full-length GLI2 to enter the nucleus as a transcriptional activator of target genes including GLI1, PTCH1, and HHIP (a negative-feedback loop gene) PMID:20956384.
Bifunctional GLI2 processing: In the absence of SHH signal, GLI2 is partially proteolyzed into a truncated repressor form; SHH signaling suppresses this processing/degradation, tipping the balance toward the activator form PMC1447407.

Causal chain — genotype to phenotype: - Heterozygous truncating/loss-of-function GLI2 variant → GLI2 haploinsufficiency → reduced SHH-pathway transcriptional output in ventral forebrain midline, first branchial arch/craniofacial mesenchyme, limb bud (zone of polarizing activity-adjacent tissue), and Rathke's pouch/pituitary primordium → variably penetrant developmental field defects: - Ventral forebrain/midline: failure of prosencephalic cleavage in the most severe cases (classic HPE structural spectrum: alobar > semilobar > lobar > middle interhemispheric variant) — but in most GLI2 carriers, midline signaling is sufficient for cleavage and only subtler midfacial hypoplasia results. - Rathke's pouch/anterior pituitary: defective organogenesis → hypoplastic anterior pituitary, ectopic posterior pituitary lobe, panhypopituitarism. - Limb bud (postaxial zone): postaxial polydactyly, reflecting a role for GLI2/SHH signaling in anteroposterior limb patterning distinct from (and postaxial rather than the SHH/GLI3-ZRS preaxial pattern typical of ZRS-associated syndromes). - First branchial arch derivatives: mandibular hypoplasia, ear anomalies, cleft lip/palate, TMJ anomalies. - Incomplete penetrance is best explained mechanistically by the mouse gene-environment model: a single functional GLI2 allele provides sufficient pathway output for normal development under baseline conditions, but reduced buffering capacity renders development vulnerable to additional genetic or environmental "second hits" (teratogen exposure, stochastic developmental variation, possible modifier alleles in other pathway genes) PMID:27585885.

Cellular processes: Neural progenitor patterning/ventralization in the neural tube and forebrain (GO:0021871, "morphogenesis of embryonic epithelium," and GO:0021854, "hypothalamus development," among relevant GO terms); craniofacial neural crest cell patterning; anterior pituitary progenitor (Rathke's pouch) proliferation and differentiation; limb bud mesenchymal patterning.

Protein dysfunction: Predominantly loss-of-function/haploinsufficiency — truncated proteins lacking the C-terminal activator domain fail to drive SHH target-gene transcription; some act with residual repressor activity, potentially producing partial dominant-negative effects, though most literature frames the mechanism as simple haploinsufficiency.

Tissue damage mechanism: Not applicable in the classic "tissue injury" sense — this is a developmental patterning defect, not a degenerative or destructive process; the pathology is one of failed morphogenesis rather than secondary tissue injury (with the caveat that untreated endocrine deficiency can secondarily cause metabolic tissue stress, e.g., hypoglycemic injury).

Suggested GO/CL/UBERON terms for pathophysiology modeling: - GO:0007224 Smoothened signaling pathway - GO:0021871 forebrain regionalization / GO:0021983 pituitary gland development - GO:0060173 limb development / GO:0060174 limb bud formation - CL:0002573 Schwann cell (not directly relevant) — more relevant: CL:0000710 neurectodermal cell / CL:0002028 basal cell of epithelium of Rathke's pouch (if available) / generic "neural progenitor cell" CL:0011020 - UBERON:0002298 brainstem / UBERON:0001891 midbrain (less relevant); most relevant: UBERON:0002264 pars distalis of adenohypophysis, UBERON:0002037 cerebellum (not affected); primary sites: UBERON:0000955 brain (forebrain/prosencephalon), UBERON:0000007 pituitary gland, UBERON:0002544 pharyngeal arch (first branchial arch), UBERON:0002544 limb bud/UBERON:0004357 hand

7. Anatomical Structures Affected

Organ level: - Primary: Brain (forebrain/prosencephalon — in the minority with true HPE); pituitary gland (anterior and posterior lobes); craniofacial skeleton (midface, mandible, maxilla); limbs (hands/feet — postaxial polydactyly). - Secondary/complication-related: Endocrine organs downstream of pituitary hormone axes (thyroid, adrenal glands, gonads) secondary to central hormone deficiency; eyes (hypotelorism, occasionally more severe ocular anomalies in classic HPE); ears (external ear malformations, pre-auricular tags); oral cavity (cleft lip/palate). - Body systems: Nervous system (CNS structural, and secondary seizures/intellectual disability), endocrine system (primary target of the pituitary-anomaly arm), musculoskeletal system (craniofacial, limb).

Tissue/cell level: - Ventral forebrain neuroepithelium and midline glial structures (in classic HPE cases) - Rathke's pouch epithelium / anterior pituitary hormone-secreting cell lineages (somatotropes, corticotropes, thyrotropes, gonadotropes — reflecting the multi-hormone deficiency pattern) - Cranial neural crest-derived craniofacial mesenchyme - Limb bud mesenchyme (postaxial zone) - Temporomandibular joint condylar/coronoid cartilage (a specifically noted GLI2-associated finding)

Subcellular level: Primary cilium (site of SMO/SUFU/GLI2 pathway transduction — GO:0005929 cilium; GO:0060170 ciliary membrane); nucleus (site of GLI2 transcriptional activity); cytoplasm (site of GLI2 proteolytic processing).

Localization/laterality: HPE-spectrum brain and facial anomalies are typically midline defects (bilateral, symmetric, affecting the axis of embryonic cleavage) rather than lateralized; postaxial polydactyly may be unilateral or bilateral and can affect hands, feet, or both.

8. Temporal Development

Onset: Congenital for all structural (craniofacial, limb, brain) features; pituitary hormone deficiencies may be apparent at birth (neonatal hypoglycemia, cholestatic jaundice from cortisol/GH deficiency, micropenis) or emerge over infancy/childhood as growth failure or delayed puberty becomes evident.
Onset pattern: Structural anomalies are fixed at birth (non-progressive congenital malformations); endocrine deficits, while congenital in origin (structural pituitary maldevelopment), may have an insidious, delayed-recognition clinical onset if hormone deficiency is partial or evolves.
Disease stages: Not applicable in the sense of a staged progressive disease — HPE9/Culler-Jones syndrome is a static congenital malformation/endocrinopathy rather than a degenerative condition.
Progression rate/course: Structural features are stable (non-progressive) from birth; hormone deficiencies, once established, are generally lifelong and stable with replacement therapy, though evolving multi-hormone deficiency over childhood (e.g., isolated GH deficiency progressing to panhypopituitarism) has been described in the broader hypopituitarism literature and is plausible in GLI2 cases.
Duration: Chronic, lifelong (endocrine and structural sequelae persist; surgical corrections of cleft/polydactyly are one-time interventions).
Remission: Not applicable — this is a structural/developmental condition, not a relapsing-remitting disease.
Critical periods: The relevant "critical period" is prenatal — first-trimester forebrain, craniofacial, pituitary (Rathke's pouch), and limb bud patterning windows, during which GLI2 haploinsufficiency (potentially compounded by environmental "second hits" such as maternal hyperglycemia, retinoic acid, or alcohol exposure) determines phenotypic severity.

9. Inheritance and Population

Epidemiology: - Holoprosencephaly overall occurs in ~1 in 250 conceptuses but only ~1 in 8,000–16,000 live births (most affected conceptuses are lost to spontaneous abortion); reported live-birth prevalence ranges 0.48–1.70 per 10,000 across international birth-defect surveillance systems, with a large Chinese national study finding 0.92 per 10,000 (1,222 cases / 13,284,142 births) (PMC6553724; StatPearls NBK560861). - GLI2 is a minor contributor to this overall HPE burden (<1% of classic HPE cases attributable to GLI2 point mutations), but is disproportionately represented among patients specifically ascertained for congenital hypopituitarism with polydactyly — making HPE9/Culler-Jones syndrome an important, likely underdiagnosed cause of syndromic congenital hypopituitarism. - Exact prevalence/incidence figures specific to HPE9 (as opposed to HPE overall) are not separately tabulated in Orphanet/OMIM; it should be treated as an ultra-rare disorder (likely well under 1:1,000,000, per case-series-level reporting to date).

Inheritance pattern: Autosomal dominant, with the defining features of incomplete penetrance and variable expressivity. GeneReviews explicitly notes that "[b]ecause incomplete penetrance is a feature of dominantly inherited HPE, relatively normal facial appearance can be seen in individuals who have causative gene variants and affected first degree relatives" (NBK1530).

Penetrance: Markedly incomplete — in the Roessler et al. family study, only 2/11 mutation-carrying parents had hypopituitarism, 3/11 had isolated polydactyly, and 6/11 were phenotypically normal despite carrying the identical pathogenic variant as their affected child. This is among the most striking documented penetrance figures in the monogenic HPE literature and is a key curation point.

Expressivity: Highly variable, spanning isolated polydactyly → isolated pituitary anomaly → combined craniofacial/pituitary/limb phenotype (Culler-Jones syndrome) → rare semilobar HPE.

Germline mosaicism: Not specifically documented for GLI2 in the sources reviewed, though plausible given the general dominant-inheritance, incomplete-penetrance pattern typical of HPE genes; a documented mother-and-two-daughters case series with a GLI2 deletion explicitly demonstrates "variable expressivity and incomplete penetrance" across generations (PMC7669391), consistent with vertical transmission through a mildly/subclinically affected parent.

Founder effects / consanguinity: No founder mutations or consanguinity-driven recessive component identified — consistent with autosomal dominant, not recessive, inheritance.

Carrier frequency: Not established/reported; expected to be very low given rarity and predominance of de novo or small-family case reporting.

Population demographics: No specific ethnic or geographic enrichment reported for GLI2-HPE9 itself; broader HPE literature notes higher reported (ascertainment-influenced) prevalence in some populations (African-American, Hispanic, Pakistani communities in the US) attributable to differential rates of prenatal diagnosis/termination rather than true differential incidence. Sex ratio and age-distribution data specific to HPE9 were not identified in this search.

10. Diagnostics

Clinical/laboratory tests: - Endocrine hormone panels: GH, IGF-1, cortisol/ACTH, TSH/free T4, gonadotropins (LH/FSH), prolactin — to characterize the pattern and completeness of multiple pituitary hormone deficiency (MPHD). - Electrolytes/urine osmolality/water-deprivation testing — for suspected diabetes insipidus (posterior pituitary/ADH axis).

Imaging: - Brain/pituitary MRI is the key diagnostic imaging modality. Characteristic findings in GLI2-mutation carriers with hypopituitarism: hypoplastic anterior pituitary with an ectopic posterior pituitary lobe (pituitary stalk interruption-like pattern), often without any HPE brain malformation — this pattern was specifically demonstrated in 4 evaluated patients with GLI2 mutations PMID:20685856; a further case report describes "Ectopic Posterior Pituitary, Polydactyly, Midfacial Hypoplasia and Multiple Pituitary Hormone Deficiency due to a Novel Heterozygous... Mutation in the GLI2 Gene" (PMC7499131). - In more severely affected individuals: MRI may show semilobar or lobar HPE (fused thalami, absent septum pellucidum, monoventricle, absent/hypoplastic corpus callosum, absent olfactory bulbs). - Skeletal imaging for polydactyly characterization prior to surgical planning.

Genetic testing: - Single-gene GLI2 sequencing (all coding exons) is commercially available (e.g., GTR test 583574; PreventionGenetics HPE9/GLI2 panel). - HPE gene panels (typically including SHH, ZIC2, SIX3, TGIF1, PTCH1, GLI2, and others) are the standard first-tier approach given genetic heterogeneity of HPE. - Whole-exome/genome sequencing is increasingly used, especially for atypical/expanded phenotypes ("Exome sequencing improves genetic diagnosis of congenital orofacial clefts" PMC10512413; a 2025 case report describes a de novo GLI2 missense variant identified via exome sequencing in isolated hypopituitarism with craniofacial anomalies). - Chromosomal microarray (CMA) is indicated when a contiguous 2q14 deletion is suspected (larger phenotype, additional features beyond the classic GLI2 point-mutation presentation). - Familial cascade testing is important given documented incomplete penetrance — apparently unaffected parents of a proband may carry the variant and should be counseled that normal phenotype does not exclude carrier status.

Clinical diagnostic criteria: No formal consensus diagnostic criteria specific to HPE9 exist; diagnosis rests on the combination of (a) characteristic phenotype (pituitary anomaly ± polydactyly ± midfacial hypoplasia ± cleft lip/palate, with or without HPE), and (b) confirmatory GLI2 molecular finding. Differential diagnosis includes other HPE-spectrum genes (SHH, ZIC2, SIX3, TGIF1, PTCH1), other syndromic causes of congenital hypopituitarism with polydactyly (e.g., Pallister-Hall syndrome, GLI3-related — a related GLI-family gene with an analogous polydactyly/hypothalamic hamartoma phenotype and important genetic differential), and Smith-Lemli-Opitz syndrome (cholesterol synthesis defect that phenocopies SHH-pathway disruption).

Screening: No population-based newborn screening program targets HPE9 specifically; prenatal ultrasound may detect structural HPE brain findings and polydactyly, prompting targeted prenatal genetic testing in known-carrier families.

11. Outcome/Prognosis

Survival/mortality: Prognosis is highly dependent on phenotypic severity. Isolated polydactyly or isolated mild pituitary anomaly carries an excellent prognosis with normal life expectancy. Severe (semilobar/alobar) HPE carries the poor prognosis characteristic of classic HPE generally (high perinatal/infant mortality in severe forms), but this is uncommon among GLI2 carriers specifically (only ~1/43 truncating-variant carriers had frank HPE in the reviewed literature).
Morbidity: Untreated panhypopituitarism carries risk of life-threatening adrenal crisis and hypoglycemia, particularly in the neonatal period; with recognition and hormone replacement, morbidity is substantially reduced and outcomes approach those of other causes of congenital hypopituitarism.
Complications: Adrenal crisis, severe hypoglycemia (especially neonatal), growth failure if GH deficiency undiagnosed, hypogonadism/delayed puberty, feeding/speech difficulties from cleft palate, functional limb impairment from polydactyly (usually correctable surgically).
Recovery potential: Structural anomalies are permanent (surgical correction, not cure); endocrine deficiencies are fully manageable (not curable) with lifelong hormone replacement — patients on adequate replacement generally achieve normal growth and pubertal development.
Prognostic factors: Presence and severity of brain structural HPE is the dominant prognostic determinant; truncating (vs. missense) GLI2 variants correlate with more complete/severe pituitary and polydactyly phenotypes per the Corder et al. 2022 genotype-phenotype analysis.

12. Treatment

There is no disease-modifying or curative treatment for the underlying GLI2 developmental defect; management is multidisciplinary and supportive/replacement-based.

Pharmacotherapy (hormone replacement — the mainstay of management): - Growth hormone (recombinant human GH) for GH deficiency — MAXO term: consider MAXO:0000950 (supportive care) or a specific pharmacotherapy term paired with therapeutic_agent (somatropin; NCIT term for recombinant human growth hormone). - Hydrocortisone replacement for ACTH/cortisol deficiency (critical for preventing adrenal crisis). - Levothyroxine for central hypothyroidism (TSH deficiency). - Desmopressin (DDAVP) for central diabetes insipidus. - Sex hormone replacement (testosterone or estrogen/progesterone) at puberty for hypogonadotropic hypogonadism.

Surgical/interventional: - Polydactyly excision/reconstructive surgery — MAXO:0000004 (surgical procedure) / NCIT:C15329 (Surgical Procedure), often orthopedic (NCIT:C16186, Orthopedic Surgical Procedure). - Cleft lip/palate repair — standard craniofacial surgical protocol. - Craniofacial reconstructive surgery as needed for midfacial hypoplasia/TMJ anomalies.

Supportive/rehabilitative care: - Early developmental intervention, physical/occupational/speech therapy as indicated by neurodevelopmental status (MAXO:0000011 physical therapy; MAXO:0000930 speech therapy). - Nutritional support in infancy, particularly for feeding difficulty related to cleft palate or hypoglycemia risk.

Genetic counseling: MAXO:0000079 (genetic counseling) is essential given autosomal dominant inheritance with incomplete penetrance — counseling must explicitly address the possibility of a phenotypically normal or minimally affected (isolated polydactyly) parent carrying the causal variant, given the well-documented penetrance data above.

Experimental/targeted therapies: No GLI2-pathway-targeted or gene therapy approaches were identified as being in clinical development for HPE9 specifically. (Hedgehog-pathway small-molecule inhibitors such as SMO inhibitors exist for cancer indications — e.g., basal cell carcinoma, medulloblastoma — but these target pathway hyperactivation and are not relevant to this loss-of-function developmental disorder; no gain-of-function/agonist strategy for GLI2 haploinsufficiency was found reported.)

Treatment strategy: Management follows a standard congenital hypopituitarism algorithm (endocrinology-led, with hormone deficiencies identified and replaced sequentially/simultaneously as diagnosed) combined with craniofacial/orthopedic surgical planning for structural anomalies — essentially the same clinical pathway used for other genetic causes of congenital hypopituitarism with polydactyly (e.g., Pallister-Hall syndrome).

13. Prevention

Primary prevention: No primary prevention exists for the germline GLI2 mutation itself. For the environmentally-modulated component of the broader HPE spectrum, optimizing maternal glycemic control in diabetic pregnancies is the most evidence-supported modifiable primary-prevention measure; avoidance of retinoic acid excess and cholesterol-synthesis-inhibiting medications in pregnancy is also generally advised in the broader HPE prevention literature.
Secondary prevention (early detection): Newborn screening for hypoglycemia/jaundice in infants with any suggestive dysmorphic features (polydactyly + midfacial hypoplasia) should prompt early endocrine evaluation to prevent adrenal-crisis morbidity — this is the single most impactful secondary-prevention measure for GLI2-HPE9, given that endocrine complications (not structural anomalies) drive acute morbidity/mortality risk.
Genetic screening: Prenatal diagnosis via targeted GLI2 testing is available in families with a known pathogenic variant; given incomplete penetrance, genetic counseling must clarify that a negative family history in parents does not reduce recurrence risk if a parent is an unrecognized (subclinical) carrier.
Tertiary prevention: Lifelong monitoring and hormone-replacement adjustment to prevent complications of under- or over-replacement (e.g., adrenal crisis prevention via stress-dosing education, growth monitoring on GH therapy).
Public health/behavioral: No population-level public health intervention specific to HPE9 exists; general periconceptional counseling regarding diabetes control and teratogen avoidance applies to the broader HPE risk-reduction framework.

14. Other Species / Natural Disease

Taxonomy: Mouse (Mus musculus, NCBITaxon:10090) is the dominant model species; Gli2 is also studied in zebrafish (Danio rerio, NCBITaxon:7955) in the broader Hedgehog-signaling/craniofacial development literature, though HPE9-specific zebrafish models were not identified in this search.
Orthologous gene: Mouse Gli2 (MGI:95728), NCBI Gene ID 14633 (mouse); highly conserved zinc-finger transcription factor with essentially identical domain architecture and pathway role as human GLI2.
Natural disease in other species: No naturally occurring GLI2-mutant HPE has been reported in companion animals or wildlife in the sources reviewed (this is a modeled/engineered-mutation disease in animals, not a spontaneously occurring veterinary condition, unlike some other Mendelian disorders with OMIA entries).
Comparative pathology: Mouse Gli2 null homozygotes show floor-plate absence, foregut/lung/anorectal defects, skeletal malformations, and altered commissural neuron guidance, with most dying before E18.5 (MGI:95728). Background-strain-dependent HPE recapitulation is a key comparative-biology point (see Model Organisms below).

15. Model Organisms

Mouse Gli2 knockout (constitutive null): Homozygous Gli2-null mice are embryonic lethal (most die before E18.5) with absence of the neural tube floor plate, foregut/lung/anorectal defects, skeletal malformations, and altered commissural neuron axon guidance (MGI:95728).
Genetic-background dependence — a key model insight: On the C57BL/6J background, homozygous Gli2 loss-of-function recapitulates the characteristic brain and facial features of severe human HPE, including midfacial hypoplasia, hypotelorism, and medial forebrain deficiency with loss of ventral neurospecification. In contrast, Gli2-null mice on an outbred CD-1 background do not recapitulate the forebrain/facial HPE phenotype — directly demonstrating background-dependent modifier effects on HPE penetrance/expressivity, a strong parallel to the incomplete penetrance seen in human GLI2 carriers.
Heterozygous (haploinsufficient) mice as the more clinically relevant model: Gli2+/− heterozygous mice are phenotypically normal at baseline, closely mirroring the incompletely penetrant human carrier state, but show increased penetrance and severity of HPE-spectrum defects upon low-dose teratogen exposure — the key gene-environment interaction model for this disease (PMID:27585885; PMC5117230).
Ethanol-exposure model: Gli2 (and Shh) haploinsufficient mice show exacerbated teratogenic response to prenatal ethanol exposure, directly modeling a gene × alcohol-exposure interaction relevant to the "second hit" hypothesis for incomplete penetrance in human carriers (PMC3929747).
Model limitations: Because complete phenotype recapitulation (forebrain/facial HPE) requires both homozygous loss and a permissive (C57BL/6J) genetic background, no single mouse model directly represents the typical human HPE9 situation (heterozygous variant, phenotype ranging from normal to severe). The heterozygous + teratogen-challenge paradigm is the best available proxy for the human clinical reality of incomplete penetrance and gene-environment-dependent expressivity.
Applications: These models are used to study SHH-pathway dosage sensitivity in forebrain/craniofacial/pituitary/limb patterning, to dissect genetic-background modifier effects on penetrance, and to test specific environmental teratogen interactions (diabetes-like hyperglycemia models, retinoic acid, ethanol, cholesterol-pathway inhibitors) relevant to human risk-factor counseling.
Resources: MGI (Mouse Genome Informatics) — Gli2 gene page MGI:95728; specific targeted allele MGI:2158720.

Summary of Key Curation Points for a Dismech Entry

Two-tier phenotype framing is essential: HPE9 nominally denotes GLI2-caused HPE, but the dominant, best-evidenced human phenotype is the pituitary anomaly + postaxial polydactyly + subtle facial features presentation (formally split out as Culler-Jones syndrome, OMIM #615849) — true brain-cleavage HPE is a minority presentation in GLI2 carriers (~1/43 truncating-variant carriers). A dismech entry should model this spectrum explicitly, likely with has_subtypes distinguishing the classic-HPE-with-forebrain-cleavage presentation from the pituitary/polydactyly-predominant presentation, and should consider cross-referencing/coordinating with a separate Culler-Jones syndrome entry if one exists or is planned (grouping candidate).
Incomplete penetrance is the single most citable, well-quantified fact (Roessler 2003: 2/11 hypopituitarism, 3/11 isolated polydactyly, 6/11 unaffected among mutation-carrying parents) — ideal for the Inheritance block and for genetic-counseling notes.
Mechanism module fit: This disease is a strong candidate for conforms_to a Sonic Hedgehog / GLI2-pathway–anchored pathophysiology node (SUFU-GLI2 dissociation → nuclear GLI2 activator function → target-gene transcription in forebrain/pituitary/limb/craniofacial primordia), and pairs naturally with the mouse gene-environment (Gli2 haploinsufficiency × teratogen) model as HUMAN_MODEL_MISMATCH/mechanistic-hypothesis material explaining penetrance variability.
Primary citable sources: Roessler et al. 2003 (PMID:14581620, founding paper), Bertolacini et al. 2012 (PMID:21204792, phenotypic variability cohort), Corder et al. 2022 (AJMG-A, genotype-phenotype truncating vs. zinc-finger), and the 2010 PubMed:20685856 imaging paper are the core human-clinical evidence base; PMID:27585885 and PMC3929747 are the core model-organism (MODEL_ORGANISM evidence_source) sources for the gene-environment mechanism.

Sources: - Entry - #610829 - HOLOPROSENCEPHALY 9; HPE9 - OMIM - Entry - *165230 - GLI-KRUPPEL FAMILY MEMBER 2; GLI2 - OMIM - Entry - #615849 - CULLER-JONES SYNDROME; CJS - OMIM - Holoprosencephaly Overview - GeneReviews - NCBI Bookshelf (NBK1530) - Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features - PubMed (PMID:14581620) - Clinical findings in patients with GLI2 mutations – phenotypic variability - PMC (PMID:21204792) - Truncating and zinc‐finger variants in GLI2 are associated with hypopituitarism - Corder et al. 2022 - AJMG-A - Novel heterozygous nonsense GLI2 mutations in patients with hypopituitarism and ectopic posterior pituitary lobe without holoprosencephaly - PubMed (PMID:20685856) - Ectopic Posterior Pituitary, Polydactyly, Midfacial Hypoplasia and MPHD due to a Novel GLI2 Mutation - PMC - A patient with a mild holoprosencephaly spectrum phenotype and heterotaxy and a 1.3 Mb deletion encompassing GLI2 - PubMed (PMID:22106008) - Role of GLI2 in hypopituitarism phenotype - Journal of Molecular Endocrinology - Case Report: A case of Culler-Jones syndrome caused by GLI2 gene mutation - Frontiers/PMC - A case series of a mother and two daughters with a GLI2 gene deletion demonstrating variable expressivity and incomplete penetrance - PMC - Gli2 gene-environment interactions contribute to the etiological complexity of holoprosencephaly: evidence from a mouse model - PMC (PMID:27585885) - The Teratogenic Effects of Prenatal Ethanol Exposure Are Exacerbated by Sonic Hedgehog or Gli2 Haploinsufficiency in the Mouse - PMC - Gli2 MGI Mouse Gene Detail - MGI:95728 - Sonic hedgehog Signaling Regulates Gli2 Transcriptional Activity by Suppressing Its Processing and Degradation - PMC - A mechanism for vertebrate Hedgehog signaling: recruitment to cilia and dissociation of SuFu-Gli protein complexes - PubMed - The interplay of Patched, Smoothened and cholesterol in Hedgehog signaling - ScienceDirect - Regulation of Gli2 and Gli3 activities by an amino-terminal repression domain - PubMed (PMID:10433919) - Epidemiological characteristics of holoprosencephaly in China, 2007-2014 - PMC - Holoprosencephaly - StatPearls - NCBI Bookshelf (NBK560861) - Holoprosencephaly: Review of Embryology, Clinical Phenotypes, Etiology and Management - MDPI Children - The unfolding clinical spectrum of holoprosencephaly due to mutations in SHH, ZIC2, SIX3 and TGIF genes - EJHG - Holoprosencephaly 9 - MalaCards - NM_001374353.1(GLI2):c.4612T>C (p.Ser1538Pro) AND Holoprosencephaly 9 - ClinVar

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Holoprosencephaly 9 (HPE9, GLI2-Related Holoprosencephaly): Comprehensive Research Report

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome/Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Summary of Key Curation Points for a Dismech Entry