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Classifications

ISDS Skeletal Nosology

👪

Inheritance

1

Autosomal recessive inheritance HP:0000007

Affected individuals carry biallelic RNU4ATAC variants, reported so far as compound heterozygous genotypes, and the syndrome was recognized as an autosomal recessive trait from affected sib pairs with unaffected parents before its gene was known.

Autosomal recessive inheritance

Show evidence (3 references)

PMID:29265708 SUPPORT Human clinical

"It has an autosomal recessive pattern of inheritance."

States the inheritance pattern of Lowry-Wood syndrome in the report that established its genetic cause.

PMID:3706411 SUPPORT Human clinical

"We describe a brother and a sister with a syndrome of short stature, microcephaly, mental retardation, and multiple epiphyseal dysplasia. The parents were normal."

An affected sib pair of both sexes with unaffected parents, the clinical basis for the autosomal recessive inference.

PMID:36795902 SUPPORT Human clinical

"RNU4atac-opathy is inherited in an autosomal recessive manner."

GeneReviews states the inheritance of the RNU4ATAC spectrum, of which Lowry-Wood syndrome is one named phenotype.

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Discussions and Knowledge Gaps

1

What determines whether a biallelic RNU4ATAC genotype produces Lowry-Wood syndrome rather than Roifman syndrome or MOPD I, given that some alleles recur in all three?

KNOWLEDGE GAP lws_rnu4atac_allele_phenotype_determinant

Attached to

pathophysiology#Biallelic Hypomorphic RNU4ATAC Variants

The proposed rule that two severe alleles give MOPD I and a severe plus a mild allele give Roifman syndrome did not fit the first molecularly confirmed Lowry-Wood patient, whose two variants both lie in regions predicted to matter for splicing. Variant severity alone does not explain the phenotype, and modifier genes or tissue-specific splicing thresholds remain open possibilities.

Show evidence (2 references)

PMID:29265708 SUPPORT Human clinical

"The mechanism through which RNU4ATAC variants cause different clinical phenotypes is unclear."

States the open question directly.

PMID:29265708 SUPPORT Human clinical

"However, both of the variants in patient 1 are in regions predicted by Merico et al. to be important for splicing (Supplemental Figure S1), which is inconsistent with their theory."

The observation that contradicts the severe-plus-mild allele rule.

⚙

Pathophysiology

3

Biallelic Hypomorphic RNU4ATAC Variants

RNU4ATAC (2q14.2) is a non-protein-coding gene for U4atac snRNA. Lowry-Wood syndrome arises from biallelic variants that impair, but do not abolish, U4atac function. Compared with MOPD I, whose variants concentrate in the 5' stem-loop needed for U4atac/U6atac.U5 tri-snRNP formation, the variants reported in Lowry-Wood syndrome are dispersed across the RNA and affect less conserved nucleotides, which fits its milder phenotype. The correlation is imperfect: the same alleles (for example n.46G>A and n.111G>A) recur across all three named RNU4ATAC phenotypes.

RNU4ATAC hgnc:34016

U4atac base-pairing with U6atac snRNA GO:0030624 ↓ DECREASED

Downstream

Defective U12-Type Minor Intron Splicing

Show evidence (4 references)

PMID:29265708 SUPPORT Human clinical

"Here, we describe three patients with Lowry Wood syndrome with biallelic RNU4ATAC pathogenic variants."

Establishes biallelic RNU4ATAC variants as the cause of the syndrome.

PMID:29265708 SUPPORT INDIRECT Human clinical

"where they are likely to disrupt both internal pairing to form the loop structure and essential base-pairing with u6atac"

The first confirmed patient's two variants are predicted, not shown, to disrupt U4atac base-pairing with U6atac, the molecular function bound on this node.

PMID:30368667 SUPPORT Human clinical

"FitCons scores for nucleotides mutated in the more severe MOPD are higher than RS or LWS and that they were more frequently located in the 5' Stem-Loop of the RNA critical for the formation of the U4/U6.U5 tri-snRNP complex, whereas the variants are more dispersed in the other conditions"

Supports the genotype-phenotype pattern placing Lowry-Wood variants at less conserved, more dispersed positions than MOPD I variants.

+ 1 more reference

Defective U12-Type Minor Intron Splicing

U4atac base-pairs with U6atac and is required to excise U12-type (minor) introns, present in roughly 750 human genes. In peripheral blood mononuclear cells from an adult with Lowry-Wood syndrome, minor intron retention was markedly elevated over his heterozygous father and healthy controls, and alternative splicing around minor introns was increased, so the splicing lesion has been measured directly in this phenotype rather than only inferred from MOPD I and Roifman syndrome.

U12-type (minor) intron splicing GO:0000398 ↓ DECREASED

U12-type (minor) spliceosome GO:0005689

Downstream

Secondary Primary Cilium Dysfunction

Decreased Serum Immunoglobulins Low IgG and IgM without clinical immunodeficiency have been documented in Lowry-Wood syndrome. In Roifman syndrome the corresponding defect is a transitional B-cell arrest from disturbed minor splicing of MAPK1, but that route has not been studied in Lowry-Wood syndrome.

Show evidence (4 references)

PMID:30368667 SUPPORT Human clinical

"Pathogenic variants in RNU4ATAC, an RNA of the minor spliceosome important for the excision of U12-dependent introns, have been recently associated with LWS."

Places the causal gene in the minor (U12-dependent) splicing pathway.

PMID:33660780 SUPPORT Human clinical

"This revealed that the median %MSIRet was significantly elevated in the individual with Lowry–Wood syndrome (60%) compared to the unaffected carrier (26%) and the unrelated healthy controls (P< 0.0001)."

Direct measurement of increased minor intron retention in cells from a patient with Lowry-Wood syndrome.

PMID:33660780 SUPPORT Human clinical

"we detected alternatively spliced MIG transcripts in peripheral blood mononuclear cells (PBMCs) from individuals with Roifman syndrome (RNU4ATAC), Lowry–Wood syndrome (RNU4ATAC) and early-onset cerebellar ataxia (RNU12), suggesting they contribute to disease pathogenesis"

Adds increased alternative splicing of minor-intron-containing genes in Lowry-Wood patient cells.

+ 1 more reference

Secondary Primary Cilium Dysfunction

Cilium assembly is over-represented among minor-intron-containing genes, and U4atac deficiency alters primary cilium function in patient fibroblasts and causes ciliopathy-related traits in a u4atac zebrafish model. This is the proposed route from the splicing lesion to the skeletal, retinal and brain features of the RNU4ATAC spectrum. It was shown across RNU4ATAC patients, not specifically in Lowry-Wood syndrome, and the steps from cilium dysfunction to epiphyseal dysplasia or microcephaly have not been demonstrated, so the edges below are marked as indirect.

cilium assembly GO:0060271 ↓ DECREASED

Animal models

u4atac zebrafish morphant (Khatri 2023) Zebrafish partially recapitulates u4atac deficiency produces ciliopathy-related phenotypes and ciliary defects, supporting the cilium arm of the RNU4ATAC mechanism.

Downstream

Multiple Epiphyseal Dysplasia

Microcephaly

Retinal Dystrophy

Developmental Delay and Intellectual Disability

Short Stature

Show evidence (3 references)

PMID:36802443 SUPPORT INDIRECT In vitro / ex vivo

"alterations of primary cilium function in TALS and JBTS-like patient fibroblasts"

Altered primary cilium function in fibroblasts from patients with other RNU4ATAC genotypes (MOPD I and a Joubert-like presentation). Not shown in Lowry-Wood syndrome specifically.

PMID:36802443 SUPPORT INDIRECT Human clinical

"indicating ciliary dysfunction as a mechanism downstream of minor splicing defects"

States that ciliary dysfunction follows from the splicing defect rather than being a parallel lesion.

PMID:36802443 SUPPORT INDIRECT Model organism

"our data indicate that alteration of cilium biogenesis is part of the physiopathological mechanisms of TALS/RFMN/LWS, secondarily to defects of minor intron splicing"

The authors' conclusion names Lowry-Wood syndrome (LWS) among the phenotypes whose mechanism includes altered cilium biogenesis. The conclusion rests on patient fibroblasts from MOPD I and Joubert-like cases and on the zebrafish model, so for Lowry-Wood syndrome it is an inference rather than a direct observation.

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Pathograph

Use Group by to collapse related nodes into one box. Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

13

Blood 1

Decreased Serum Immunoglobulins OCCASIONAL Decreased circulating immunoglobulin concentration HP:0004313

Show evidence (2 references)

PMID:29265708 SUPPORT Human clinical

"immunologic testing was pursued, which demonstrated low IgG and IgM levels in the absence of a clear clinical immunodeficiency"

Documents low immunoglobulins without clinical immunodeficiency in a confirmed patient.

PMID:42322193 SUPPORT BACKGROUND Human clinical

"variable short stature, developmental delay, eye involvement and subclinical immunodeficiency"

Describes the immunodeficiency of Lowry-Wood syndrome as subclinical.

Eye 2

Congenital Nystagmus FREQUENT HP:0000639

Onset: CONGENITAL

Show evidence (1 reference)

PMID:12605445 SUPPORT Human clinical

"Lowry-Wood syndrome (LWS) is a rare condition characterized by multiple epiphyseal dysplasia (MED), microcephaly, and congenital nystagmus."

Congenital nystagmus is one of the defining features.

Retinal Dystrophy OCCASIONAL HP:0000556

Show evidence (2 references)

PMID:19288552 SUPPORT Human clinical

"microcephaly, short stature, multiple epiphyseal dysplasia, tapetoretinal degeneration, and mental retardation"

Retinal degeneration in a clinically diagnosed patient.

PMID:29265708 SUPPORT Human clinical

"retinitis pigmentosa (no night vision, with peripheral vision loss and retinal pigmentary clumping)"

Retinal dystrophy in a molecularly confirmed patient.

Head and Neck 1

Microcephaly VERY_FREQUENT HP:0000252

Show evidence (3 references)

PMID:29265708 SUPPORT Human clinical

"Characteristic features include multiple epiphyseal dysplasia and microcephaly."

Microcephaly is one of the two characteristic features.

PMID:29265708 SUPPORT Human clinical

"At 10 years and 9 months, she had an OFC of 41.2 cm (Z-score −8.6)"

Quantifies the severity of microcephaly in a confirmed patient.

PMID:36795902 SUPPORT Human clinical

"Findings present in all affected individuals include growth restriction, microcephaly, skeletal dysplasia, and cognitive impairment."

GeneReviews lists microcephaly among the findings present in every individual across the RNU4ATAC spectrum, of which Lowry-Wood syndrome is one named phenotype. The statement covers the spectrum, not Lowry-Wood syndrome alone.

Limbs 5

Hip Dislocation OCCASIONAL HP:0002827

Show evidence (2 references)

PMID:29265708 SUPPORT Human clinical

"contractures of the elbows bilaterally, and bilateral femoral head dislocations"

Bilateral femoral head dislocation in a molecularly confirmed sib pair.

PMID:19288552 SUPPORT Human clinical

"dislocation of both hips with severe hip dysplasia"

Bilateral hip dislocation in a clinically diagnosed patient.

Patellar Dislocation OCCASIONAL HP:0002999

Show evidence (1 reference)

PMID:19288552 SUPPORT Human clinical

"lateral dislocation of both patellae"

Bilateral patellar dislocation in a clinically diagnosed patient.

Limited Elbow Extension OCCASIONAL HP:0001377

Show evidence (2 references)

PMID:19288552 SUPPORT Human clinical

"Bilateral restricted elbow extension, knock knees and hip dislocation were also present."

Restricted elbow extension in a clinically diagnosed patient.

PMID:29265708 SUPPORT Human clinical

"contractures of the elbows bilaterally"

Bilateral elbow contractures in a molecularly confirmed sib pair.

Coxa Vara OCCASIONAL HP:0002812

Show evidence (2 references)

PMID:2801767 SUPPORT Human clinical

"We report on a brother and sister with epiphyseal dysplasia and coxa vara, microcephaly, and short stature."

Coxa vara in a clinically diagnosed sib pair.

PMID:29265708 SUPPORT Human clinical

"the brother had scoliosis and coxa vara"

Coxa vara in a molecularly confirmed patient.

Fifth Finger Clinodactyly FREQUENT Clinodactyly of the 5th finger HP:0004209

Show evidence (1 reference)

PMID:29265708 SUPPORT Human clinical

"Both had full lips, prominent nose, sloping forehead, brachyclinodactyly V"

Fifth-finger brachyclinodactyly in a molecularly confirmed sib pair, also reported in patient 1 of the same series.

Musculoskeletal 1

Multiple Epiphyseal Dysplasia VERY_FREQUENT HP:0002654

Show evidence (4 references)

PMID:30368667 SUPPORT Human clinical

"Lowry-Wood syndrome (LWS) is a skeletal dysplasia characterized by multiple epiphyseal dysplasia associated with microcephaly, developmental delay and intellectual disability, and eye involvement."

Names multiple epiphyseal dysplasia as the characterizing skeletal finding.

PMID:29265708 SUPPORT Human clinical

"Lowry Wood syndrome (LWS; OMIM #226969) is characterized by multiple epiphyseal dysplasia (MED) without spinal involvement"

Specifies that the dysplasia spares the spine. The OMIM number in this quote is the source's own and is not adopted here.

PMID:19288552 SUPPORT Human clinical

"multiple epiphyseal dysplasia that was more severe at the proximal femoral epiphyses"

Radiographic distribution in a clinically diagnosed patient.

+ 1 more reference

Nervous System 1

Developmental Delay and Intellectual Disability FREQUENT HP:0001249

Show evidence (3 references)

PMID:30368667 SUPPORT Human clinical

"multiple epiphyseal dysplasia associated with microcephaly, developmental delay and intellectual disability, and eye involvement"

Developmental delay and intellectual disability are listed among the defining features.

PMID:2801767 REFUTE Human clinical

"In the sibs we describe, mental retardation is not apparent"

Clinically diagnosed sibs without intellectual disability, showing the feature is not invariable. This family was never molecularly confirmed.

PMID:36795902 SUPPORT Human clinical

"Findings present in all affected individuals include growth restriction, microcephaly, skeletal dysplasia, and cognitive impairment."

GeneReviews lists cognitive impairment among the findings present in every individual across the RNU4ATAC spectrum, of which Lowry-Wood syndrome is one named phenotype. The statement covers the spectrum, not Lowry-Wood syndrome alone. It sits beside the REFUTE item above, from clinically diagnosed sibs with normal intelligence who were never molecularly confirmed.

Growth 2

Short Stature FREQUENT HP:0004322

Show evidence (3 references)

PMID:3706411 SUPPORT Human clinical

"the syndrome first described by Lowry and Wood ... in two boys who had epiphyseal dysplasia, short stature, microcephaly, and nystagmus"

Short stature is part of the original description.

PMID:42322193 SUPPORT BACKGROUND Human clinical

"with microcephaly and multiple epiphyseal dysplasia, along with variable short stature, developmental delay, eye involvement and subclinical immunodeficiency"

Describes short stature in Lowry-Wood syndrome as variable.

PMID:36795902 SUPPORT Human clinical

"Findings present in all affected individuals include growth restriction, microcephaly, skeletal dysplasia, and cognitive impairment."

GeneReviews lists growth restriction among the findings present in every individual across the RNU4ATAC spectrum, of which Lowry-Wood syndrome is one named phenotype. The statement covers the spectrum, not Lowry-Wood syndrome alone.

Intrauterine Growth Retardation OCCASIONAL HP:0001511

Show evidence (1 reference)

PMID:29265708 SUPPORT BACKGROUND Human clinical

"Intrauterine growth restriction, short stature, congenital nystagmus, retinitis pigmentosa, elbow contractures, coxa vara, and joint dislocations have also been described"

Summarizes the earlier clinical literature, which reported intrauterine growth restriction among the additional features.

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Genetic Associations

1

RNU4ATAC

Gene: RNU4ATAC hgnc:34016 gene page relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (3 references)

PMID:29265708 SUPPORT Human clinical

"This report expands the phenotypic spectrum for biallelic RNU4ATAC disorder causing variants and is the first to establish the genetic cause for Lowry Wood syndrome."

First report establishing RNU4ATAC as the causal gene.

PMID:30368667 SUPPORT Human clinical

"We report RNU4ATAC pathogenic variants in two further patients."

Independent replication in further patients.

PMID:32628740 SUPPORT Human clinical

"Only one other variant was found in all three RNU4ATAC-associated syndromes, namely n.46G>A (one TALS, one RFMN and one LWS families)."

Shows a single allele recurring across all three named phenotypes.

🗃️

External Assertions

1

OMIM Lowry-Wood syndrome record

OMIM disease record OMIM:226960

OMIM phenotype entry for Lowry-Wood syndrome. The number is taken from the ISDS 2023 nosology row for the syndrome; Farach et al. 2018 (PMID:29265708) prints 226969 instead.

Show evidence (1 reference)

PMID:36779427 SUPPORT Other

"Multiple epiphyseal dysplasia with microcephaly and nystagmus (Lowry-Wood syndrome), RNU4ATAC-related | AR | RNU4ATAC | 226960"

The ISDS 2023 table row for Lowry-Wood syndrome gives OMIM 226960.

💊

Medical Actions

1

Multidisciplinary Supportive Care

Action: Multidisciplinary supportive care Ontology label: Supportive Care NCIT:C15747

No disease-specific therapy exists. Management is supportive, including orthopedic follow-up of the skeletal dysplasia and immunological assessment, with antibiotics or immunoglobulin replacement where an antibody deficiency is clinically significant, and immunological evaluation before live vaccines.

Show evidence (2 references)

PMID:36795902 SUPPORT Other

"Supportive care to improve quality of life, maximize function, and reduce complications is recommended. This ideally involves multidisciplinary care by specialists in relevant fields, including orthopedists to monitor the associated skeletal dysplasia and immunologists"

GeneReviews management recommendation for the RNU4ATAC spectrum.

PMID:36795902 SUPPORT Other

"Perform immunologic evaluation prior to administration of live vaccines."

GeneReviews advice behind the immunological evaluation before live vaccines named in this treatment's description.

🔬

Diagnosis

1

Targeted RNU4ATAC Sequencing (Biallelic pathogenic variants in affected individuals)

Diagnosis is confirmed by finding biallelic pathogenic RNU4ATAC variants in a person with suggestive findings. Because exome capture designed around protein-coding exons may miss the gene, targeted or Sanger sequencing of RNU4ATAC is recommended when epiphyseal dysplasia occurs with microcephaly, intellectual disability, immunodeficiency, or retinal anomalies.

Show evidence (2 references)

PMID:29265708 SUPPORT Human clinical

"Since RNU4ATAC is not consistently targeted in standard exome capture methodologies that only target protein-coding exons, many such cases will be missed. Sanger sequencing of this locus is needed for a complete assessment."

States why targeted sequencing is needed.

PMID:36795902 SUPPORT Human clinical

"The diagnosis of RNU4atac-opathy is established in a proband with suggestive findings and biallelic pathogenic (or likely pathogenic) variants in RNU4ATAC identified by molecular genetic testing."

GeneReviews diagnostic criterion for the RNU4ATAC spectrum.

📊

Prevalence

1

Worldwide (published cases)

Cases/families reported in the literature Rare

No population frequency has been published. A 2026 reevaluation of 98 previously reported individuals with biallelic RNU4ATAC variants found 5 with a Lowry-Wood syndrome diagnosis, making it the least often diagnosed of the three named RNU4ATAC phenotypes.

Show evidence (2 references)

PMID:29265708 SUPPORT Human clinical

"The features also overlap with Lowry Wood syndrome, another rare but well-defined skeletal dysplasia"

Describes Lowry-Wood syndrome as rare.

PMID:41808109 SUPPORT Human clinical

"29/98 (29.6%) with RS and only 5/98 (5.1%) with LWS"

Counts the published individuals carrying a Lowry-Wood syndrome diagnosis among those reviewed.

🔀

Differential Diagnoses

3

Conditions with similar clinical presentations that must be differentiated from Lowry-Wood Syndrome:

Microcephalic Osteodysplastic Primordial Dwarfism Type I MONDO:0008871

Overlapping Features The severe allelic RNU4ATAC phenotype, with spondyloepimetaphyseal dysplasia, profound growth failure, brain malformations and death in early childhood for most patients.

Distinguishing Features

MOPD I is a spondyloepimetaphyseal dysplasia; Lowry-Wood syndrome is a multiple epiphyseal dysplasia without spinal involvement
Growth failure and overall severity are much greater in MOPD I

Show evidence (2 references)

PMID:29265708 SUPPORT Human clinical

"MOPDI/III is an SEMD, Roifman syndrome is an SED, and LWS is an MED."

The radiographic distinction between the three RNU4ATAC phenotypes.

PMID:29265708 SUPPORT Human clinical

"The conditions are on a spectrum, with the short stature and overall phenotype associated with MOPDI/III being more severe than LWS and Roifman syndrome."

Relative severity of MOPD I.

Roifman Syndrome MONDO:0014722

Overlapping Features The allelic RNU4ATAC phenotype defined by symptomatic antibody deficiency with spondyloepiphyseal dysplasia, growth retardation and retinal dystrophy.

Distinguishing Features

Roifman syndrome has spinal involvement (spondyloepiphyseal dysplasia)
Antibody deficiency is clinically significant in Roifman syndrome and subclinical in Lowry-Wood syndrome

Show evidence (2 references)

PMID:29265708 SUPPORT Human clinical

"MOPDI/III is an SEMD, Roifman syndrome is an SED, and LWS is an MED."

The radiographic distinction between Roifman and Lowry-Wood syndromes.

PMID:36622817 SUPPORT Human clinical

"Although historically described as discrete conditions they appear to represent a phenotypic spectrum with clinical features not always aligning with diagnostic categories."

Cautions that individual patients may not fit one named phenotype.

🐁

Animal Models

1

u4atac zebrafish morphant (Khatri 2023)

Morpholino knockdown of zebrafish u4atac targeting the 5' stem-loop or stem II. Phenotypes were rescued by wild-type human U4atac but not by U4atac carrying patient variants.

Species

Zebrafish

Genotype

u4atac antisense morpholino knockdown (5' stem-loop or stem II)

Publication

PMID:36802443

Pathograph links

Secondary Primary Cilium Dysfunction partially recapitulates fidelity: low observes: tissue u4atac deficiency produces ciliopathy-related phenotypes and ciliary defects, supporting the cilium arm of the RNU4ATAC mechanism.

Limitations: Transient, dose-dependent morpholino knockdown rather than a patient genotype, read out in embryos. The model is not specific to Lowry-Wood syndrome: the patient variants tested for rescue came from other RNU4ATAC phenotypes, and the fish phenotypes (body axis curvature, pronephric cysts, otolith defects) are not the epiphyseal dysplasia that defines Lowry-Wood syndrome.

Show evidence (1 reference)

PMID:36802443 SUPPORT Model organism

"u4atac zebrafish model, which exhibits ciliopathy-related phenotypes and ciliary defects. These phenotypes could be rescued by WT but not by pathogenic variants-carrying human U4atac."

Knockdown phenotypes and their allele-specific rescue support the model as informative for the cilium node.

{ }

Source YAML

click to show

name: Lowry-Wood Syndrome
creation_date: "2026-10-26T00:00:00Z"
description: >-
  Lowry-Wood syndrome is a rare autosomal recessive skeletal dysplasia caused by
  biallelic pathogenic variants in RNU4ATAC, which encodes the U4atac small
  nuclear RNA of the minor (U12-dependent) spliceosome. Its defining features
  are multiple epiphyseal dysplasia without spinal involvement together with
  microcephaly, accompanied by variable short stature, developmental delay or
  intellectual disability, eye involvement (congenital nystagmus, retinal
  dystrophy), joint dislocations and contractures, and subclinical antibody
  deficiency. It is the mildest of the three historically named RNU4ATAC
  phenotypes, alongside microcephalic osteodysplastic primordial dwarfism type I
  and Roifman syndrome, and the three are now regarded as points on one
  phenotypic spectrum (RNU4atac-opathy).
category: Mendelian
parents:
- Skeletal Dysplasia
- Spliceosomopathy
synonyms:
- Lowry Wood syndrome
- LWS
- RNU4ATAC-related Lowry-Wood syndrome
- Multiple epiphyseal dysplasia with microcephaly and nystagmus
disease_term:
  preferred_term: Lowry-Wood syndrome
  term:
    id: MONDO:0009191
    label: Lowry-Wood syndrome
references:
- reference: PMID:36795902
  title: RNU4atac-opathy.
  tags:
  - GeneReviews
  findings: []
classifications:
  isds_skeletal_category:
  - classification_value: multiple_epiphyseal_dysplasia_and_pseudoachondroplasia
    notes: >-
      ISDS Nosology of Genetic Skeletal Disorders, 2023 revision (Unger et al.,
      PMID:36779427), group 9 "Pseudoachondroplasia and the multiple epiphyseal
      dysplasias", NOS 09-0110. The committee places Lowry-Wood syndrome in
      this group and its allelic RNU4ATAC phenotypes, MOPD I and Roifman
      syndrome, in the primordial dwarfism group (group 21), so the separate
      dismech entries follow the nosology.
    evidence:
    - reference: PMID:36779427
      reference_title: "Nosology of genetic skeletal disorders: 2023 revision."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Multiple epiphyseal dysplasia with microcephaly and nystagmus (Lowry-Wood syndrome), RNU4ATAC-related | AR | RNU4ATAC | 226960"
      explanation: >-
        The ISDS 2023 table row placing Lowry-Wood syndrome in group 9, with its
        inheritance, gene and OMIM number.
external_assertions:
- name: OMIM Lowry-Wood syndrome record
  source: OMIM
  assertion_type: disease_record
  external_id: OMIM:226960
  url: https://omim.org/entry/226960
  description: >-
    OMIM phenotype entry for Lowry-Wood syndrome. The number is taken from the
    ISDS 2023 nosology row for the syndrome; Farach et al. 2018 (PMID:29265708)
    prints 226969 instead.
  evidence:
  - reference: PMID:36779427
    reference_title: "Nosology of genetic skeletal disorders: 2023 revision."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Multiple epiphyseal dysplasia with microcephaly and nystagmus (Lowry-Wood syndrome), RNU4ATAC-related | AR | RNU4ATAC | 226960"
    explanation: >-
      The ISDS 2023 table row for Lowry-Wood syndrome gives OMIM 226960.
inheritance:
- name: Autosomal recessive inheritance
  description: >-
    Affected individuals carry biallelic RNU4ATAC variants, reported so far as
    compound heterozygous genotypes, and the syndrome was recognized as an
    autosomal recessive trait from affected sib pairs with unaffected parents
    before its gene was known.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It has an autosomal recessive pattern of inheritance."
    explanation: >-
      States the inheritance pattern of Lowry-Wood syndrome in the report that
      established its genetic cause.
  - reference: PMID:3706411
    reference_title: "Syndrome of short stature, microcephaly, mental retardation, and multiple epiphyseal dysplasia--Lowry-Wood syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We describe a brother and a sister with a syndrome of short stature, microcephaly, mental retardation, and multiple epiphyseal dysplasia. The parents were normal."
    explanation: >-
      An affected sib pair of both sexes with unaffected parents, the clinical
      basis for the autosomal recessive inference.
  - reference: PMID:36795902
    reference_title: RNU4atac-opathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "RNU4atac-opathy is inherited in an autosomal recessive manner."
    explanation: >-
      GeneReviews states the inheritance of the RNU4ATAC spectrum, of which
      Lowry-Wood syndrome is one named phenotype.
prevalence:
- population: Worldwide (published cases)
  measure_type: CASES_IN_LITERATURE
  prevalence_class: RARE
  notes: >-
    No population frequency has been published. A 2026 reevaluation of 98
    previously reported individuals with biallelic RNU4ATAC variants found 5
    with a Lowry-Wood syndrome diagnosis, making it the least often diagnosed of
    the three named RNU4ATAC phenotypes.
  evidence:
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The features also overlap with Lowry Wood syndrome, another rare but well-defined skeletal dysplasia"
    explanation: Describes Lowry-Wood syndrome as rare.
  - reference: PMID:41808109
    reference_title: "Phenotypic spectrum of RNU4ATAC-related spliceosomopathies: four novel cases and integrated reevaluation of previously reported patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "29/98 (29.6%) with RS and only 5/98 (5.1%) with LWS"
    explanation: >-
      Counts the published individuals carrying a Lowry-Wood syndrome diagnosis
      among those reviewed.
pathophysiology:
- name: Biallelic Hypomorphic RNU4ATAC Variants
  conforms_to: "spliceosome_component_dysfunction#Germline Spliceosome Component Variant"
  biological_scale: MOLECULAR
  role: trigger
  description: >-
    RNU4ATAC (2q14.2) is a non-protein-coding gene for U4atac snRNA. Lowry-Wood
    syndrome arises from biallelic variants that impair, but do not abolish,
    U4atac function. Compared with MOPD I, whose variants concentrate in the
    5' stem-loop needed for U4atac/U6atac.U5 tri-snRNP formation, the variants
    reported in Lowry-Wood syndrome are dispersed across the RNA and affect less
    conserved nucleotides, which fits its milder phenotype. The correlation is
    imperfect: the same alleles (for example n.46G>A and n.111G>A) recur across
    all three named RNU4ATAC phenotypes.
  genes:
  - preferred_term: RNU4ATAC
    term:
      id: hgnc:34016
      label: RNU4ATAC
  molecular_functions:
  - preferred_term: U4atac base-pairing with U6atac snRNA
    term:
      id: GO:0030624
      label: U6atac snRNA binding
    modifier: DECREASED
  downstream:
  - target: Defective U12-Type Minor Intron Splicing
  evidence:
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we describe three patients with Lowry Wood syndrome with biallelic RNU4ATAC pathogenic variants."
    explanation: Establishes biallelic RNU4ATAC variants as the cause of the syndrome.
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: "where they are likely to disrupt both internal pairing to form the loop structure and essential base-pairing with u6atac"
    explanation: >-
      The first confirmed patient's two variants are predicted, not shown, to
      disrupt U4atac base-pairing with U6atac, the molecular function bound on
      this node.
  - reference: PMID:30368667
    reference_title: "Lowry-Wood syndrome: further evidence of association with RNU4ATAC, and correlation between genotype and phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "FitCons scores for nucleotides mutated in the more severe MOPD are higher than RS or LWS and that they were more frequently located in the 5' Stem-Loop of the RNA critical for the formation of the U4/U6.U5 tri-snRNP complex, whereas the variants are more dispersed in the other conditions"
    explanation: >-
      Supports the genotype-phenotype pattern placing Lowry-Wood variants at
      less conserved, more dispersed positions than MOPD I variants.
  - reference: PMID:32628740
    reference_title: "Clinical interpretation of variants identified in RNU4ATAC, a non-coding spliceosomal gene."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "variants found in RFMN patients were globally associated with stronger effects than those identified in TALS patients, while those identified in LWS had the lowest effects"
    explanation: >-
      A splicing-efficiency assay of RNU4ATAC variants found the smallest
      functional effects for Lowry-Wood alleles, consistent with hypomorphic
      variants.
- name: Defective U12-Type Minor Intron Splicing
  conforms_to: "spliceosome_component_dysfunction#Mis-Splicing of a Sensitive Transcript Subset"
  biological_scale: MOLECULAR
  description: >-
    U4atac base-pairs with U6atac and is required to excise U12-type (minor)
    introns, present in roughly 750 human genes. In peripheral blood
    mononuclear cells from an adult with Lowry-Wood syndrome, minor intron
    retention was markedly elevated over his heterozygous father and healthy
    controls, and alternative splicing around minor introns was increased, so
    the splicing lesion has been measured directly in this phenotype rather than
    only inferred from MOPD I and Roifman syndrome.
  biological_processes:
  - preferred_term: U12-type (minor) intron splicing
    term:
      id: GO:0000398
      label: mRNA splicing, via spliceosome
    modifier: DECREASED
  cellular_components:
  - preferred_term: U12-type (minor) spliceosome
    term:
      id: GO:0005689
      label: U12-type spliceosomal complex
  downstream:
  - target: Secondary Primary Cilium Dysfunction
  - target: Decreased Serum Immunoglobulins
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Low IgG and IgM without clinical immunodeficiency have been documented in
      Lowry-Wood syndrome. In Roifman syndrome the corresponding defect is a
      transitional B-cell arrest from disturbed minor splicing of MAPK1, but
      that route has not been studied in Lowry-Wood syndrome.
  evidence:
  - reference: PMID:30368667
    reference_title: "Lowry-Wood syndrome: further evidence of association with RNU4ATAC, and correlation between genotype and phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pathogenic variants in RNU4ATAC, an RNA of the minor spliceosome important for the excision of U12-dependent introns, have been recently associated with LWS."
    explanation: Places the causal gene in the minor (U12-dependent) splicing pathway.
  - reference: PMID:33660780
    reference_title: "Disruption of exon-bridging interactions between the minor and major spliceosomes results in alternative splicing around minor introns."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This revealed that the median %MSIRet was significantly elevated in the individual with Lowry–Wood syndrome (60%) compared to the unaffected carrier (26%) and the unrelated healthy controls (P< 0.0001)."
    explanation: >-
      Direct measurement of increased minor intron retention in cells from a
      patient with Lowry-Wood syndrome.
  - reference: PMID:33660780
    reference_title: "Disruption of exon-bridging interactions between the minor and major spliceosomes results in alternative splicing around minor introns."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we detected alternatively spliced MIG transcripts in peripheral blood mononuclear cells (PBMCs) from individuals with Roifman syndrome (RNU4ATAC), Lowry–Wood syndrome (RNU4ATAC) and early-onset cerebellar ataxia (RNU12), suggesting they contribute to disease pathogenesis"
    explanation: >-
      Adds increased alternative splicing of minor-intron-containing genes in
      Lowry-Wood patient cells.
  - reference: PMID:36802443
    reference_title: "Deficiency of the minor spliceosome component U4atac snRNA secondarily results in ciliary defects in human and zebrafish."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: "In the human genome, about 750 genes contain one intron excised by the minor spliceosome."
    explanation: Gives the size of the gene set whose splicing depends on U4atac.
- name: Secondary Primary Cilium Dysfunction
  biological_scale: CELLULAR
  description: >-
    Cilium assembly is over-represented among minor-intron-containing genes, and
    U4atac deficiency alters primary cilium function in patient fibroblasts and
    causes ciliopathy-related traits in a u4atac zebrafish model. This is the
    proposed route from the splicing lesion to the skeletal, retinal and brain
    features of the RNU4ATAC spectrum. It was shown across RNU4ATAC patients,
    not specifically in Lowry-Wood syndrome, and the steps from cilium
    dysfunction to epiphyseal dysplasia or microcephaly have not been
    demonstrated, so the edges below are marked as indirect.
  biological_processes:
  - preferred_term: cilium assembly
    term:
      id: GO:0060271
      label: cilium assembly
    modifier: DECREASED
  downstream:
  - target: Multiple Epiphyseal Dysplasia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Microcephaly
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Retinal Dystrophy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Developmental Delay and Intellectual Disability
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Short Stature
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  evidence:
  - reference: PMID:36802443
    reference_title: "Deficiency of the minor spliceosome component U4atac snRNA secondarily results in ciliary defects in human and zebrafish."
    supports: SUPPORT
    evidence_source: IN_VITRO
    directness: INDIRECT
    snippet: "alterations of primary cilium function in TALS and JBTS-like patient fibroblasts"
    explanation: >-
      Altered primary cilium function in fibroblasts from patients with other
      RNU4ATAC genotypes (MOPD I and a Joubert-like presentation). Not shown in
      Lowry-Wood syndrome specifically.
  - reference: PMID:36802443
    reference_title: "Deficiency of the minor spliceosome component U4atac snRNA secondarily results in ciliary defects in human and zebrafish."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: "indicating ciliary dysfunction as a mechanism downstream of minor splicing defects"
    explanation: >-
      States that ciliary dysfunction follows from the splicing defect rather
      than being a parallel lesion.
  - reference: PMID:36802443
    reference_title: "Deficiency of the minor spliceosome component U4atac snRNA secondarily results in ciliary defects in human and zebrafish."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    directness: INDIRECT
    snippet: "our data indicate that alteration of cilium biogenesis is part of the physiopathological mechanisms of TALS/RFMN/LWS, secondarily to defects of minor intron splicing"
    explanation: >-
      The authors' conclusion names Lowry-Wood syndrome (LWS) among the
      phenotypes whose mechanism includes altered cilium biogenesis. The
      conclusion rests on patient fibroblasts from MOPD I and Joubert-like cases
      and on the zebrafish model, so for Lowry-Wood syndrome it is an
      inference rather than a direct observation.
phenotypes:
- category: Skeletal
  name: Multiple Epiphyseal Dysplasia
  phenotype_term:
    preferred_term: Multiple epiphyseal dysplasia
    term:
      id: HP:0002654
      label: Multiple epiphyseal dysplasia
  frequency: VERY_FREQUENT
  description: >-
    The defining skeletal feature. The epiphyses are affected without spinal
    involvement, which separates Lowry-Wood syndrome from the
    spondyloepiphyseal dysplasia of Roifman syndrome and the
    spondyloepimetaphyseal dysplasia of MOPD I. The proximal femoral epiphyses
    can be the most severely affected.
  evidence:
  - reference: PMID:30368667
    reference_title: "Lowry-Wood syndrome: further evidence of association with RNU4ATAC, and correlation between genotype and phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Lowry-Wood syndrome (LWS) is a skeletal dysplasia characterized by multiple epiphyseal dysplasia associated with microcephaly, developmental delay and intellectual disability, and eye involvement."
    explanation: Names multiple epiphyseal dysplasia as the characterizing skeletal finding.
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Lowry Wood syndrome (LWS; OMIM #226969) is characterized by multiple epiphyseal dysplasia (MED) without spinal involvement"
    explanation: >-
      Specifies that the dysplasia spares the spine. The OMIM number in this
      quote is the source's own and is not adopted here.
  - reference: PMID:19288552
    reference_title: "Multiple joint dislocations: an additional skeletal finding in Lowry-Wood syndrome?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "multiple epiphyseal dysplasia that was more severe at the proximal femoral epiphyses"
    explanation: Radiographic distribution in a clinically diagnosed patient.
  - reference: PMID:36795902
    reference_title: RNU4atac-opathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Findings present in all affected individuals include growth restriction, microcephaly, skeletal dysplasia, and cognitive impairment."
    explanation: >-
      GeneReviews lists skeletal dysplasia among the findings present in every individual
      across the RNU4ATAC spectrum, of which Lowry-Wood syndrome is one named
      phenotype. The statement covers the spectrum, not Lowry-Wood syndrome
      alone.
- category: Neurological
  name: Microcephaly
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  frequency: VERY_FREQUENT
  description: >-
    Present from birth and progressive in the molecularly confirmed patients,
    whose head circumference fell to between 5 and 9 standard deviations below
    the mean by late childhood.
  evidence:
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Characteristic features include multiple epiphyseal dysplasia and microcephaly."
    explanation: Microcephaly is one of the two characteristic features.
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At 10 years and 9 months, she had an OFC of 41.2 cm (Z-score −8.6)"
    explanation: Quantifies the severity of microcephaly in a confirmed patient.
  - reference: PMID:36795902
    reference_title: RNU4atac-opathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Findings present in all affected individuals include growth restriction, microcephaly, skeletal dysplasia, and cognitive impairment."
    explanation: >-
      GeneReviews lists microcephaly among the findings present in every individual
      across the RNU4ATAC spectrum, of which Lowry-Wood syndrome is one named
      phenotype. The statement covers the spectrum, not Lowry-Wood syndrome
      alone.
- category: Growth
  name: Short Stature
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  frequency: FREQUENT
  description: >-
    Short stature is usual but its degree varies, and it is milder than the
    primordial dwarfism of MOPD I. Low birth length is documented in confirmed
    patients.
  evidence:
  - reference: PMID:3706411
    reference_title: "Syndrome of short stature, microcephaly, mental retardation, and multiple epiphyseal dysplasia--Lowry-Wood syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the syndrome first described by Lowry and Wood ... in two boys who had epiphyseal dysplasia, short stature, microcephaly, and nystagmus"
    explanation: Short stature is part of the original description.
  - reference: PMID:42322193
    reference_title: "RNU4ATAC-opathy: Clinical, molecular, and transcriptomic insights from a large cohort."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: "with microcephaly and multiple epiphyseal dysplasia, along with variable short stature, developmental delay, eye involvement and subclinical immunodeficiency"
    explanation: Describes short stature in Lowry-Wood syndrome as variable.
  - reference: PMID:36795902
    reference_title: RNU4atac-opathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Findings present in all affected individuals include growth restriction, microcephaly, skeletal dysplasia, and cognitive impairment."
    explanation: >-
      GeneReviews lists growth restriction among the findings present in every individual
      across the RNU4ATAC spectrum, of which Lowry-Wood syndrome is one named
      phenotype. The statement covers the spectrum, not Lowry-Wood syndrome
      alone.
- category: Growth
  name: Intrauterine Growth Retardation
  phenotype_term:
    preferred_term: Intrauterine growth retardation
    term:
      id: HP:0001511
      label: Intrauterine growth retardation
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: "Intrauterine growth restriction, short stature, congenital nystagmus, retinitis pigmentosa, elbow contractures, coxa vara, and joint dislocations have also been described"
    explanation: >-
      Summarizes the earlier clinical literature, which reported intrauterine
      growth restriction among the additional features.
- category: Neurological
  name: Developmental Delay and Intellectual Disability
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  frequency: FREQUENT
  description: >-
    Usually mild. Developmental delay with later mild intellectual disability
    is documented in confirmed patients, but a clinically diagnosed sib pair had
    normal intelligence, so cognition is not uniformly affected.
  evidence:
  - reference: PMID:30368667
    reference_title: "Lowry-Wood syndrome: further evidence of association with RNU4ATAC, and correlation between genotype and phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "multiple epiphyseal dysplasia associated with microcephaly, developmental delay and intellectual disability, and eye involvement"
    explanation: Developmental delay and intellectual disability are listed among the defining features.
  - reference: PMID:2801767
    reference_title: "Epiphyseal dysplasia with coxa vara, microcephaly, and normal intelligence in sibs: expanded spectrum of Lowry-Wood syndrome?"
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "In the sibs we describe, mental retardation is not apparent"
    explanation: >-
      Clinically diagnosed sibs without intellectual disability, showing the
      feature is not invariable. This family was never molecularly confirmed.
  - reference: PMID:36795902
    reference_title: RNU4atac-opathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Findings present in all affected individuals include growth restriction, microcephaly, skeletal dysplasia, and cognitive impairment."
    explanation: >-
      GeneReviews lists cognitive impairment among the findings present in every individual
      across the RNU4ATAC spectrum, of which Lowry-Wood syndrome is one named
      phenotype. The statement covers the spectrum, not Lowry-Wood syndrome
      alone.
      It sits beside the REFUTE item above, from clinically diagnosed sibs
      with normal intelligence who were never molecularly confirmed.
- category: Ophthalmological
  name: Congenital Nystagmus
  phenotype_term:
    preferred_term: Congenital nystagmus
    term:
      id: HP:0000639
      label: Nystagmus
    onset:
      onset_category: CONGENITAL
  frequency: FREQUENT
  evidence:
  - reference: PMID:12605445
    reference_title: A new patient with Lowry-Wood syndrome with mild phenotype.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Lowry-Wood syndrome (LWS) is a rare condition characterized by multiple epiphyseal dysplasia (MED), microcephaly, and congenital nystagmus."
    explanation: Congenital nystagmus is one of the defining features.
- category: Ophthalmological
  name: Retinal Dystrophy
  phenotype_term:
    preferred_term: Retinal dystrophy
    term:
      id: HP:0000556
      label: Retinal dystrophy
  frequency: OCCASIONAL
  description: >-
    Reported as tapetoretinal degeneration and as retinitis pigmentosa with
    night blindness and peripheral field loss. Shared with Roifman syndrome.
  evidence:
  - reference: PMID:19288552
    reference_title: "Multiple joint dislocations: an additional skeletal finding in Lowry-Wood syndrome?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "microcephaly, short stature, multiple epiphyseal dysplasia, tapetoretinal degeneration, and mental retardation"
    explanation: Retinal degeneration in a clinically diagnosed patient.
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "retinitis pigmentosa (no night vision, with peripheral vision loss and retinal pigmentary clumping)"
    explanation: Retinal dystrophy in a molecularly confirmed patient.
- category: Skeletal
  name: Hip Dislocation
  phenotype_term:
    preferred_term: Hip dislocation
    term:
      id: HP:0002827
      label: Hip dislocation
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "contractures of the elbows bilaterally, and bilateral femoral head dislocations"
    explanation: Bilateral femoral head dislocation in a molecularly confirmed sib pair.
  - reference: PMID:19288552
    reference_title: "Multiple joint dislocations: an additional skeletal finding in Lowry-Wood syndrome?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "dislocation of both hips with severe hip dysplasia"
    explanation: Bilateral hip dislocation in a clinically diagnosed patient.
- category: Skeletal
  name: Patellar Dislocation
  phenotype_term:
    preferred_term: Patellar dislocation
    term:
      id: HP:0002999
      label: Patellar dislocation
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:19288552
    reference_title: "Multiple joint dislocations: an additional skeletal finding in Lowry-Wood syndrome?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "lateral dislocation of both patellae"
    explanation: Bilateral patellar dislocation in a clinically diagnosed patient.
- category: Skeletal
  name: Limited Elbow Extension
  phenotype_term:
    preferred_term: Limited elbow extension
    term:
      id: HP:0001377
      label: Limited elbow extension
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:19288552
    reference_title: "Multiple joint dislocations: an additional skeletal finding in Lowry-Wood syndrome?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bilateral restricted elbow extension, knock knees and hip dislocation were also present."
    explanation: Restricted elbow extension in a clinically diagnosed patient.
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "contractures of the elbows bilaterally"
    explanation: Bilateral elbow contractures in a molecularly confirmed sib pair.
- category: Skeletal
  name: Coxa Vara
  phenotype_term:
    preferred_term: Coxa vara
    term:
      id: HP:0002812
      label: Coxa vara
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:2801767
    reference_title: "Epiphyseal dysplasia with coxa vara, microcephaly, and normal intelligence in sibs: expanded spectrum of Lowry-Wood syndrome?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report on a brother and sister with epiphyseal dysplasia and coxa vara, microcephaly, and short stature."
    explanation: Coxa vara in a clinically diagnosed sib pair.
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the brother had scoliosis and coxa vara"
    explanation: Coxa vara in a molecularly confirmed patient.
- category: Skeletal
  name: Fifth Finger Clinodactyly
  phenotype_term:
    preferred_term: Brachyclinodactyly of the fifth finger
    term:
      id: HP:0004209
      label: Clinodactyly of the 5th finger
  frequency: FREQUENT
  evidence:
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Both had full lips, prominent nose, sloping forehead, brachyclinodactyly V"
    explanation: Fifth-finger brachyclinodactyly in a molecularly confirmed sib pair, also reported in patient 1 of the same series.
- category: Immunologic
  name: Decreased Serum Immunoglobulins
  phenotype_term:
    preferred_term: Low IgG and IgM
    term:
      id: HP:0004313
      label: Decreased circulating immunoglobulin concentration
  frequency: OCCASIONAL
  description: >-
    Usually subclinical. Low IgG and IgM have been found on testing without a
    clinical immunodeficiency, in contrast to the symptomatic antibody
    deficiency that defines Roifman syndrome. Immune testing has not been done
    in most reported patients, so the frequency is uncertain.
  evidence:
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "immunologic testing was pursued, which demonstrated low IgG and IgM levels in the absence of a clear clinical immunodeficiency"
    explanation: Documents low immunoglobulins without clinical immunodeficiency in a confirmed patient.
  - reference: PMID:42322193
    reference_title: "RNU4ATAC-opathy: Clinical, molecular, and transcriptomic insights from a large cohort."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: "variable short stature, developmental delay, eye involvement and subclinical immunodeficiency"
    explanation: Describes the immunodeficiency of Lowry-Wood syndrome as subclinical.
genetic:
- name: RNU4ATAC
  gene_term:
    preferred_term: RNU4ATAC
    term:
      id: hgnc:34016
      label: RNU4ATAC
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  notes: >-
    Reported Lowry-Wood genotypes are compound heterozygous, for example
    n.51G>A with n.5A>C, n.111G>A with n.46G>A, and n.120T>G with n.114G>C.
    Several alleles are shared with MOPD I and Roifman syndrome, so the allele
    pair rather than any single variant decides the phenotype. RNU4ATAC is a
    small non-coding gene that standard exome capture may not cover, which is a
    recognized cause of missed diagnoses.
  evidence:
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This report expands the phenotypic spectrum for biallelic RNU4ATAC disorder causing variants and is the first to establish the genetic cause for Lowry Wood syndrome."
    explanation: First report establishing RNU4ATAC as the causal gene.
  - reference: PMID:30368667
    reference_title: "Lowry-Wood syndrome: further evidence of association with RNU4ATAC, and correlation between genotype and phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report RNU4ATAC pathogenic variants in two further patients."
    explanation: Independent replication in further patients.
  - reference: PMID:32628740
    reference_title: "Clinical interpretation of variants identified in RNU4ATAC, a non-coding spliceosomal gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Only one other variant was found in all three RNU4ATAC-associated syndromes, namely n.46G>A (one TALS, one RFMN and one LWS families)."
    explanation: Shows a single allele recurring across all three named phenotypes.
diagnosis:
- name: Targeted RNU4ATAC Sequencing
  presence: Biallelic pathogenic variants in affected individuals
  description: >-
    Diagnosis is confirmed by finding biallelic pathogenic RNU4ATAC variants in
    a person with suggestive findings. Because exome capture designed around
    protein-coding exons may miss the gene, targeted or Sanger sequencing of
    RNU4ATAC is recommended when epiphyseal dysplasia occurs with microcephaly,
    intellectual disability, immunodeficiency, or retinal anomalies.
  evidence:
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Since RNU4ATAC is not consistently targeted in standard exome capture methodologies that only target protein-coding exons, many such cases will be missed. Sanger sequencing of this locus is needed for a complete assessment."
    explanation: States why targeted sequencing is needed.
  - reference: PMID:36795902
    reference_title: RNU4atac-opathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of RNU4atac-opathy is established in a proband with suggestive findings and biallelic pathogenic (or likely pathogenic) variants in RNU4ATAC identified by molecular genetic testing."
    explanation: GeneReviews diagnostic criterion for the RNU4ATAC spectrum.
treatments:
- name: Multidisciplinary Supportive Care
  description: >-
    No disease-specific therapy exists. Management is supportive, including
    orthopedic follow-up of the skeletal dysplasia and immunological assessment,
    with antibiotics or immunoglobulin replacement where an antibody deficiency
    is clinically significant, and immunological evaluation before live
    vaccines.
  treatment_term:
    preferred_term: Multidisciplinary supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:36795902
    reference_title: RNU4atac-opathy.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Supportive care to improve quality of life, maximize function, and reduce complications is recommended. This ideally involves multidisciplinary care by specialists in relevant fields, including orthopedists to monitor the associated skeletal dysplasia and immunologists"
    explanation: GeneReviews management recommendation for the RNU4ATAC spectrum.
  - reference: PMID:36795902
    reference_title: RNU4atac-opathy.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Perform immunologic evaluation prior to administration of live vaccines."
    explanation: >-
      GeneReviews advice behind the immunological evaluation before live
      vaccines named in this treatment's description.
animal_models:
- name: u4atac zebrafish morphant (Khatri 2023)
  species: Zebrafish
  genotype: u4atac antisense morpholino knockdown (5' stem-loop or stem II)
  publication: PMID:36802443
  description: >-
    Morpholino knockdown of zebrafish u4atac targeting the 5' stem-loop or
    stem II. Phenotypes were rescued by wild-type human U4atac but not by
    U4atac carrying patient variants.
  modeled_mechanisms:
  - target: Secondary Primary Cilium Dysfunction
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    model_scale: TISSUE
    description: >-
      u4atac deficiency produces ciliopathy-related phenotypes and ciliary
      defects, supporting the cilium arm of the RNU4ATAC mechanism.
    limitations: >-
      Transient, dose-dependent morpholino knockdown rather than a patient
      genotype, read out in embryos. The model is not specific to Lowry-Wood
      syndrome: the patient variants tested for rescue came from other
      RNU4ATAC phenotypes, and the fish phenotypes (body axis curvature,
      pronephric cysts, otolith defects) are not the epiphyseal dysplasia that
      defines Lowry-Wood syndrome.
    evidence:
    - reference: PMID:36802443
      reference_title: "Deficiency of the minor spliceosome component U4atac snRNA secondarily results in ciliary defects in human and zebrafish."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "u4atac zebrafish model, which exhibits ciliopathy-related phenotypes and ciliary defects. These phenotypes could be rescued by WT but not by pathogenic variants-carrying human U4atac."
      explanation: >-
        Knockdown phenotypes and their allele-specific rescue support the model
        as informative for the cilium node.
differential_diagnoses:
- name: Microcephalic Osteodysplastic Primordial Dwarfism Type I
  description: >-
    The severe allelic RNU4ATAC phenotype, with spondyloepimetaphyseal dysplasia,
    profound growth failure, brain malformations and death in early childhood
    for most patients.
  disease_term:
    preferred_term: microcephalic osteodysplastic primordial dwarfism type I
    term:
      id: MONDO:0008871
      label: microcephalic osteodysplastic primordial dwarfism type I
  distinguishing_features:
  - MOPD I is a spondyloepimetaphyseal dysplasia; Lowry-Wood syndrome is a multiple epiphyseal dysplasia without spinal involvement
  - Growth failure and overall severity are much greater in MOPD I
  evidence:
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MOPDI/III is an SEMD, Roifman syndrome is an SED, and LWS is an MED."
    explanation: The radiographic distinction between the three RNU4ATAC phenotypes.
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The conditions are on a spectrum, with the short stature and overall phenotype associated with MOPDI/III being more severe than LWS and Roifman syndrome."
    explanation: Relative severity of MOPD I.
- name: Roifman Syndrome
  description: >-
    The allelic RNU4ATAC phenotype defined by symptomatic antibody deficiency
    with spondyloepiphyseal dysplasia, growth retardation and retinal dystrophy.
  disease_term:
    preferred_term: Roifman syndrome
    term:
      id: MONDO:0014722
      label: Roifman syndrome
  distinguishing_features:
  - Roifman syndrome has spinal involvement (spondyloepiphyseal dysplasia)
  - Antibody deficiency is clinically significant in Roifman syndrome and subclinical in Lowry-Wood syndrome
  evidence:
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MOPDI/III is an SEMD, Roifman syndrome is an SED, and LWS is an MED."
    explanation: The radiographic distinction between Roifman and Lowry-Wood syndromes.
  - reference: PMID:36622817
    reference_title: Delineating the phenotype of RNU4ATAC-related spliceosomopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although historically described as discrete conditions they appear to represent a phenotypic spectrum with clinical features not always aligning with diagnostic categories."
    explanation: Cautions that individual patients may not fit one named phenotype.
- name: COMP-Related Multiple Epiphyseal Dysplasia
  description: >-
    Autosomal dominant multiple epiphyseal dysplasia from COMP variants produces
    similar epiphyseal changes but without microcephaly, eye involvement or
    intellectual disability. COMP analysis was negative in a patient with the
    mildest reported Lowry-Wood presentation.
  distinguishing_features:
  - Microcephaly and congenital nystagmus point to Lowry-Wood syndrome
  - COMP-related MED is autosomal dominant
  evidence:
  - reference: PMID:12605445
    reference_title: A new patient with Lowry-Wood syndrome with mild phenotype.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report a new case of MED and microcephaly, without other additional features, suggesting a mild form of LWS. Molecular analysis of the cartilage oligomeric matrix protein (COMP) gene was performed and failed to find mutations."
    explanation: COMP-related MED was considered and excluded in a mild Lowry-Wood case.
discussions:
- discussion_id: lws_rnu4atac_allele_phenotype_determinant
  kind: KNOWLEDGE_GAP
  prompt: >-
    What determines whether a biallelic RNU4ATAC genotype produces Lowry-Wood
    syndrome rather than Roifman syndrome or MOPD I, given that some alleles
    recur in all three?
  rationale: >-
    The proposed rule that two severe alleles give MOPD I and a severe plus a
    mild allele give Roifman syndrome did not fit the first molecularly
    confirmed Lowry-Wood patient, whose two variants both lie in regions
    predicted to matter for splicing. Variant severity alone does not explain
    the phenotype, and modifier genes or tissue-specific splicing thresholds
    remain open possibilities.
  attaches_to:
  - pathophysiology#Biallelic Hypomorphic RNU4ATAC Variants
  evidence:
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mechanism through which RNU4ATAC variants cause different clinical phenotypes is unclear."
    explanation: States the open question directly.
  - reference: PMID:29265708
    reference_title: The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, both of the variants in patient 1 are in regions predicted by Merico et al. to be important for splicing (Supplemental Figure S1), which is inconsistent with their theory."
    explanation: The observation that contradicts the severe-plus-mild allele rule.
notes: >-
  The clinical reports from before 2018 (Nevin 1986, Hankenson 1989, Yamamoto
  1995, Brunetti-Pierri 2003, Magnani 2009) diagnosed Lowry-Wood syndrome on
  clinical grounds only, and none was molecularly confirmed. They are cited here
  for features also seen in confirmed patients. The 1995 report of corpus
  callosum hypoplasia and leukonychia (PMID:7747786) is not encoded as a
  phenotype because the authors themselves presented it only as a possible
  variant of the syndrome. The OMIM number is 226960, as listed in the ISDS
  2023 nosology (PMID:36779427) and the later RNU4ATAC literature; Farach et
  al. 2018 prints 226969, which disagrees with both.

  Features reported across RNU4ATAC cohorts but not yet documented in a
  patient diagnosed with Lowry-Wood syndrome are not encoded as phenotypes
  here: chilblain-like skin lesions with enhanced type I interferon signalling
  (PMID:40415209), and reduced JAK1 signalling, shown in Roifman syndrome
  patients and a Drosophila U4atac mutant (PMID:42463491). The same applies to
  the cerebral anomalies reported across the RNU4ATAC spectrum (PMID:42322193):
  no brain malformation of the kind seen in MOPD I has been reported in a
  molecularly confirmed Lowry-Wood patient, where the only intracranial
  finding is an arachnoid cyst in patient 1 of PMID:29265708. The clinically
  diagnosed 1995 case with corpus callosum hypoplasia (PMID:7747786) is the
  exception noted above.

📚

References & Deep Research

References

1

PMID:36795902

RNU4atac-opathy.

No top-level findings curated for this source.

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (1)

Create: Lowry-Wood syndrome · 2026-10-26T03:48:39Z · View source

New entry for Lowry-Wood syndrome (MONDO:0009191), the third named RNU4ATAC phenotype, alongside the existing MOPD I and Roifman syndrome entries. The pathograph runs from biallelic hypomorphic RNU4ATAC variants to defective U12-type minor intron splicing, which has been measured directly in Lowry-Wood patient PBMCs (PMID:33660780), and then through secondary primary cilium dysfunction, the RNU4ATAC-wide mechanism from PMID:36802443, to the skeletal, retinal and neurodevelopmental phenotypes. The cilium-to-phenotype edges are marked INDIRECT_UNKNOWN_INTERMEDIATES and the cilium evidence is marked directness INDIRECT, because it was not shown in Lowry-Wood syndrome specifically. Phenotypes come from the two molecularly confirmed series (PMID:29265708, PMID:30368667) and the earlier clinical reports, which the entry notes identify as clinically diagnosed only. The 1995 corpus callosum and leukonychia report is deliberately not encoded as a phenotype. No OMIM mapping is recorded, because Farach 2018 gives 226969 and later papers give 226960. The two mechanism nodes conform to the spliceosome_component_dysfunction module at the same nodes as the MOPD I and Roifman entries. The change deletes stubs/Lowry-Wood_Syndrome.yaml and adds the entry as a member of the RNU4ATAC_Spectrum_Disorder grouping, which dismech PR 15656 created while this entry was in progress. A review round added GeneReviews spectrum-level evidence, a GO:0030624 U6atac snRNA binding function on the trigger node, a u4atac zebrafish animal model, and an OpenScientist deep-research report (research/Lowry-Wood_Syndrome-deep-research-openscientist.md; 18/18 citations verified). The report's identity was checked manually against MONDO:0009191 and RNU4ATAC because the MONDO build for just preflight-dr was absent; its additional leads (chilblain-like lesions, JAK/STAT signalling, U11 mouse models, an MOPD I fetal family) concern the wider spectrum or other diagnoses, so they are named in notes rather than encoded. Validated with just validate-disorders (schema, terms, 58/58 snippets).

OpenScientist ▸

Lowry-Wood Syndrome (MONDO:0009191): A Comprehensive Disease Characteristics Report

openscientist-autonomous 18 citations 2026-10-27T18:20:40.589048

Lowry-Wood Syndrome (MONDO:0009191): A Comprehensive Disease Characteristics Report

MONDO: MONDO:0009191 · Causal gene: RNU4ATAC (RNA, U4atac small nuclear; HGNC:34140; gene OMIM 601428; chr 2q14.2) · Orphanet: ORPHA:2648 · Category: Mendelian, autosomal recessive

Summary

Lowry-Wood syndrome (LWS; MONDO:0009191) is an ultra-rare, autosomal-recessive skeletal dysplasia caused by biallelic loss-of-function variants in RNU4ATAC, a non-coding, single-exon gene on chromosome 2q14.2 (HGNC:34140; OMIM 601428) that is transcribed into the U4atac small nuclear RNA (snRNA) — a core component of the minor (U12-dependent) spliceosome. Although the disorder's descriptive synonym ("Multiple epiphyseal dysplasia with microcephaly and nystagmus") emphasizes the skeletal and ophthalmologic triad, the causal lesion is not in a cartilage or eye gene but in a housekeeping RNA required for excision of ~700–800 "minor" (U12-type) introns scattered across the genome. LWS represents the mildest end of a clinical spectrum of RNU4ATAC-opathies that also includes Roifman syndrome (RS) and the severe, often perinatally lethal microcephalic osteodysplastic primordial dwarfism type 1 (MOPD1 / Taybi-Linder syndrome).

The defining clinical features of LWS are multiple epiphyseal dysplasia (causing short stature and joint/limb anomalies), microcephaly, developmental delay / intellectual disability (typically mild), and eye involvement (nystagmus and progressive retinal dystrophy). Across the broader RNU4ATAC-opathy spectrum, additional management-relevant features include immune deficiency (antibody deficiency, low B-cell subsets), cerebral anomalies, and chilblain-like skin lesions. Genotype–phenotype analyses show that severity is governed largely by variant position within the U4atac RNA secondary structure: the most severe MOPD1-causing variants cluster in the functionally constrained 5′ stem-loop critical for U4/U6.U5 tri-snRNP assembly, whereas milder LWS and RS variants are more dispersed.

The unifying molecular mechanism is transcriptome-wide retention and mis-splicing of U12-type minor introns, demonstrated by RNA-seq in patient cells and consistent across the spectrum. This minor-intron splicing defect depletes self-amplifying neural progenitors (producing microcephaly), disrupts chondro-osseous development (producing epiphyseal dysplasia and short stature), and secondarily perturbs ciliary function, JAK/STAT signaling, and type I interferon responses (contributing to immune and skin phenotypes). Diagnosis hinges on sequencing the non-coding RNU4ATAC exon — frequently missed by standard exome pipelines — with RNA-seq minor-intron-retention as a functional biomarker that enables variant reclassification. No disease-modifying therapy exists; management is supportive and multidisciplinary, with genetic counseling for the 25% recurrence risk.

Key Findings

Finding 1 — LWS is caused by biallelic variants in the non-coding minor-spliceosome gene RNU4ATAC

Exome sequencing across multiple families established that LWS results from biallelic (homozygous or compound heterozygous) pathogenic variants in RNU4ATAC, which transcribes the U4atac snRNA of the minor (U12-dependent) spliceosome. Farach et al. (2018) first established the genetic cause, describing "three patients with Lowry Wood syndrome with biallelic RNU4ATAC pathogenic variants" and stating that their report "is the first to establish the genetic cause for Lowry Wood syndrome" (PMID: 29265708). Shelihan et al. (2018) confirmed the association, noting that "Pathogenic variants in RNU4ATAC, an RNA of the minor spliceosome important for the excision of U12-dependent introns, have been recently associated with LWS" (PMID: 30368667). RNU4ATAC has a single non-coding exon on chromosome 2q14.2. This is a human clinical/genetic finding.

Finding 2 — RNU4ATAC disorders form a severity spectrum governed by variant location, with LWS the mildest

The RNU4ATAC-opathies constitute a continuum of severity from MOPD1 (most severe, frequently lethal) through Roifman syndrome to Lowry-Wood syndrome (mildest). Shelihan et al. (2018) analyzed all reported variants and found that "FitCons scores for nucleotides mutated in the more severe MOPD are higher than RS or LWS and that they were more frequently located in the 5' Stem-Loop of the RNA critical for the formation of the U4/U6.U5 tri-snRNP complex, whereas the variants are more dispersed in the other conditions" (PMID: 30368667). A recent integrated reevaluation confirms the spectrum "whose severity ranges from the microcephalic osteodysplastic primordial dwarfism type 1 (MOPD1) to the milder Roifman syndrome" (PMID: 41808109). Clinically the categories overlap substantially; one reported individual had "a novel genotype and phenotype spanning all three disorders" (PMID: 36622817), supporting the view of a single phenotypic continuum rather than discrete diseases.

Finding 3 — Core clinical phenotype: multiple epiphyseal dysplasia, microcephaly, short stature, developmental delay, and eye involvement

LWS is defined as "a skeletal dysplasia characterized by multiple epiphyseal dysplasia associated with microcephaly, developmental delay and intellectual disability, and eye involvement" (PMID: 30368667). In the largest RNU4ATAC-opathy cohort reported to date (n = 60), "Core features in this cohort—present in most individuals assessed and varying in severity—include microcephaly, short stature, skeletal anomalies, developmental delay, cerebral anomalies, skin conditions, and immune deficiency" (PMID: 42322193). Eye involvement in LWS prominently includes nystagmus (reflected in the descriptive synonym) and progressive retinal dystrophy.

Finding 4 — Mechanism: defective U4atac impairs the minor spliceosome, causing transcriptome-wide minor (U12-type) intron retention

The U4atac snRNA is "a minor spliceosome component that is essential for minor intron splicing" (PMID: 26522830). The minor spliceosome excises ~700–800 U12-dependent introns (~0.5–1% of all human introns) found in a functionally diverse set of genes. Pathogenic RNU4ATAC variants impair this machinery: RNA-seq of patient cells "confirms extensive and specific defects of minor intron splicing" (PMID: 26522830), and across the large cohort "all individuals who underwent RNA-seq showed a consistent pattern of minor intron retention" (PMID: 42322193). This minor-intron retention is the shared, upstream molecular consequence across the entire RNU4ATAC-opathy spectrum and provides a functional readout usable for variant reclassification.

Finding 5 — Secondary mechanisms: ciliary dysfunction, dysregulated JAK/STAT signaling, and type I interferon activation

Beyond the primary splicing defect, several downstream pathways are perturbed. (1) Ciliary dysfunction: U4atac depletion secondarily produces ciliary defects — "Deficiency of the minor spliceosome component U4atac snRNA secondarily results in ciliary defects in human and zebrafish" (PMID: 36802443) — linking minor-spliceosome deficiency to ciliopathy-like features. (2) JAK/STAT signaling: A Drosophila U4atac mutant shows reduced splicing of the JAK homolog hopscotch; "our work identifies alterations of Jak signaling as part of the pathogenesis of RNU4atac-opathy" (PMID: 42463491), implicating JAK/STAT in hematopoietic/immune pathogenesis. (3) Type I interferon: RNU4ATAC patients commonly develop painful chilblain-like skin lesions; "painful chilblain-like lesions are common in RNU4ATAC patients and are linked to dysregulated type I interferon signalling" (PMID: 40415209).

Finding 6 — Immunodeficiency and progressive retinal dystrophy are recurrent, management-relevant features

Immune deficiency — antibody deficiency, low lymphocyte and B-cell subsets, impaired B-cell maturation — is characteristic of Roifman syndrome and is now recognized even in the severe MOPD1 end of the spectrum. A report of twin sisters emphasized B-cell anomalies in MOPD1 and underscored "the importance of considering immunodeficiency in MOPDI management to reduce the risk of serious infectious episodes" (PMID: 38837402). Retinal dystrophy in RNU4ATAC-Roifman syndrome is a generalized rod-cone dystrophy: in a deeply phenotyped cohort of 10 patients, all had abnormal ERG and "nine showed generalized rod-cone dystrophy" (PMID: 37225827), with nyctalopia common and progressive visual loss on follow-up. These findings justify immunologic and ophthalmologic surveillance in LWS.

Finding 7 — LWS is an autosomal recessive disorder, first described by Lowry and Wood (1975), and is ultra-rare

Lowry and Wood (1975) first described two boys with epiphyseal dysplasia, short stature, microcephaly, and nystagmus. Nevin et al. (1986) reported a second family, noting "the second example of the syndrome first described by Lowry and Wood [1975] in two boys who had epiphyseal dysplasia, short stature, microcephaly, and nystagmus; one of these patients was mildly mentally retarded" and concluding that "The Lowry-Wood syndrome probably is an autosomal recessive trait" (PMID: 3706411). Only a few dozen molecularly confirmed RNU4ATAC-opathy patients exist worldwide (60 in the largest cohort), making LWS ultra-rare with no formal prevalence estimate.

Finding 8 — Animal models recapitulate key features: minor-spliceosome loss causes microcephaly and limb micromelia

Model-organism work supports causality between minor-spliceosome dysfunction and the cardinal LWS phenotypes. Conditional inactivation of the minor spliceosome (Rnu11/U11 ablation) in developing mouse cortex demonstrated that "Minor spliceosome inactivation causes microcephaly, owing to cell cycle defects and death of self-amplifying radial glial cells" (PMID: 30093551). In the limb, "Loss of U11 small nuclear RNA in the developing mouse limb results in micromelia" (PMID: 32665241), linking minor-spliceosome loss to skeletal dysplasia. A CRISPR Drosophila U4atac mutant reproduced growth/neurodevelopmental defects, immunodeficiency, and GI symptoms via mis-splicing of innate-immunity and hematopoiesis transcripts (PMID: 42463491), and zebrafish U4atac knockdown produced ciliary defects (PMID: 36802443).

Finding 9 — Diagnosis requires sequencing the non-coding RNU4ATAC exon; variants are frequently missed, and RNA-seq aids classification

Because RNU4ATAC is a single-exon non-coding gene, "the bioinformatic prediction algorithms assessing the effect of sequence variants on splicing or protein function are irrelevant" (PMID: 32628740), and variants "are often overlooked in analysis because of their noncoding nature" (PMID: 42322193). Some exome capture kits do not even target the gene — "RNU4ATAC is not targeted by many commercially available exome capture kits" (PMID: 37666272) — so whole-genome sequencing or targeted RNU4ATAC Sanger sequencing may be required; in one Chinese family, variants were identified only after WES was negative (PMID: 29370840). A cellular minor-intron splicing reporter assay (PMID: 32628740) and RNA-seq demonstrating minor intron retention provide functional evidence: "In 6 individuals, RNA-seq enabled the reclassification of variants of uncertain significance as likely pathogenic" (PMID: 42322193).

Finding 10 — RNU4ATAC disorders are molecularly and clinically distinct from PCNT-related MOPD type II

A critical differential-diagnosis point: the RNU4ATAC-opathies (MOPD1, Roifman, LWS) must be distinguished from the superficially similarly named microcephalic osteodysplastic primordial dwarfism type II (MOPD II), caused not by a spliceosome RNA but by loss-of-function variants in PCNT (pericentrin), a centrosomal protein. "Loss-of-function variants of this gene are responsible for microcephalic osteodysplastic primordial dwarfism type II (MOPDII), a rare inherited autosomal recessive disorder" (PMID: 37234811). MOPD II is distinguished by a high risk of cerebral aneurysms and Moyamoya vasculopathy; in one report "The boy died at 8 years of age as a result of an intracranial hemorrhage due to a cerebral aneurism associated with the Moyamoya malformation" (PMID: 37234811). This cerebrovascular risk belongs to PCNT-MOPD II, not to RNU4ATAC disorders — a distinction that affects surveillance and prognosis.

Detailed Report by Section

1. Disease Information

Overview. Lowry-Wood syndrome is an ultra-rare autosomal-recessive skeletal dysplasia (a "minor spliceosomopathy") characterized by multiple epiphyseal dysplasia, microcephaly, short stature, developmental delay/intellectual disability, and ophthalmologic abnormalities (nystagmus, retinal dystrophy). It is the mildest recognized presentation of the RNU4ATAC-opathy spectrum.

Key identifiers. | Resource | Identifier | |---|---| | MONDO | MONDO:0009191 | | Causal gene | RNU4ATAC (HGNC:34140; OMIM 601428; chr 2q14.2) | | Orphanet | ORPHA:2648 | | OMIM (disease) | Not formally recorded as a distinct phenotype MIM (LWS historically clinical; now within RNU4ATAC-opathy) | | ICD-10 | Q77.x (osteochondrodysplasia with defects of growth; best fit) | | MeSH | No dedicated LWS descriptor; indexed under osteochondrodysplasias/dwarfism |

Synonyms: Lowry Wood syndrome; LWS; RNU4ATAC-related Lowry-Wood syndrome; Multiple epiphyseal dysplasia with microcephaly and nystagmus.

Information source: Derived from aggregated disease-level resources and small published case series/cohorts (individual-patient reports pooled into cohorts such as the n = 60 RNU4ATAC-opathy study), not from EHR-scale data.

2. Etiology

Causal factor: Purely genetic — biallelic (homozygous or compound heterozygous) loss-of-function variants in RNU4ATAC (PMID: 29265708). No environmental or infectious cause.

Genetic risk factors / modifiers: The principal determinant of phenotype severity is variant position within the U4atac RNA secondary structure — 5′ stem-loop variants (high FitCons constraint) produce severe MOPD1, while more dispersed variants produce milder LWS/RS (PMID: 30368667). Compound heterozygosity combining a "severe" and a "mild" allele can yield intermediate phenotypes. No separate susceptibility loci or distinct modifier genes have been established.

Environmental / protective factors and gene–environment interactions: None identified; not applicable for a fully penetrant Mendelian recessive disorder. Consanguinity increases the chance of homozygosity in affected families (relevant to recessive inheritance generally).

3. Phenotypes

Phenotype	HPO term (suggested)	Type	Onset	Frequency	Severity/course
Multiple epiphyseal dysplasia	HP:0002656	Physical/skeletal	Congenital/childhood	Core (most)	Variable, chronic
Microcephaly	HP:0000252	Physical sign	Congenital/postnatal	Core (most)	Static/variable
Short stature	HP:0004322	Physical sign	Childhood	Core (most)	Chronic
Developmental delay / intellectual disability	HP:0001263 / HP:0001249	Behavioral/cognitive	Childhood	Common (often mild in LWS)	Static
Nystagmus	HP:0000639	Clinical sign	Infancy/childhood	Characteristic	Stable
Retinal dystrophy (rod-cone)	HP:0000510 / HP:0000548	Lab/clinical (ERG)	Childhood, progressive	Characteristic (RS end)	Progressive
Immune deficiency / antibody deficiency	HP:0002090 / HP:0004313	Laboratory	Childhood	Spectrum-dependent	Variable
Cerebral anomalies	HP:0002060	Imaging	Congenital	Common	Static
Chilblain-like skin lesions	HP:0011109	Physical	Variable	Common	Episodic

Quality-of-life impact is driven by short stature and skeletal/joint limitation (mobility), visual impairment (progressive retinal dystrophy), developmental/cognitive needs, and infection susceptibility from immune deficiency. Formal QoL instrument data (EQ-5D/SF-36) are not available for this ultra-rare disorder.

4. Genetic / Molecular Information

Causal gene: RNU4ATAC — non-coding, single-exon, transcribed into the ~130-nt U4atac snRNA; chr 2q14.2; HGNC:34140; OMIM 601428.

Pathogenic variants: All reported disease variants are single-nucleotide changes or small indels in the non-coding RNA; because there is no protein product, variant classes are described by location in the RNA structure rather than missense/nonsense terminology. Recurrent/illustrative variants include n.51G>A (the most frequent MOPD1-causative 5′ stem-loop variant), n.50G>A / n.55G>A (compound het in MOPD1-phenotype patients), n.29T>A (MOPD1 hotspot), and more dispersed variants in milder LWS/RS. Functional consequence is loss of function of U4atac, i.e., impaired minor spliceosome assembly. Pathogenic alleles are very rare/absent in gnomAD; carrier frequency is not well established (PMID: 32628740).

Variant origin: Germline. No somatic involvement.

Modifier genes / epigenetics / chromosomal abnormalities: No established modifier genes, epigenetic signatures, or large chromosomal rearrangements; CMA and karyotype are characteristically normal (the point variants are not detected by those methods) (PMID: 29370840).

5. Environmental Information

Not applicable. LWS is a monogenic recessive disorder with no known environmental, lifestyle, or infectious contributors. (Infections may be consequences of the associated immune deficiency — e.g., HHV-6–associated encephalopathy reported in a MOPD1 patient — but infection is not a cause of the disease.)

6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation):

Biallelic loss-of-function variants in RNU4ATAC lead to a structurally/functionally defective U4atac snRNA.
Defective U4atac impairs assembly of the U4atac/U6atac.U5 tri-snRNP, the catalytic core of the minor (U12-dependent) spliceosome.
Impaired minor spliceosome results in failure to excise ~700–800 U12-type minor introns → transcriptome-wide minor-intron retention and mis-splicing (demonstrated by patient RNA-seq).
Minor-intron retention in affected transcripts reduces functional expression of the diverse minor-intron-containing genes (enriched in cell-cycle, DNA-replication, and signaling functions). 5a. In neural progenitors, this causes cell-cycle defects and death of self-amplifying radial glial cells → reduced neuron output → microcephaly and developmental delay (demonstrated in mouse Rnu11 models; inferred for humans). 5b. In the developing limb/skeleton, minor-spliceosome deficiency disrupts chondro-osseous development → epiphyseal dysplasia, short stature, micromelia (demonstrated in mouse U11 limb model; inferred for humans). 5c. (Branch) Secondary ciliary dysfunction contributes to skeletal/developmental and possibly retinal phenotypes (human + zebrafish). 5d. (Branch) Mis-splicing of JAK/STAT pathway transcripts attenuates cytokine signaling → impaired hematopoiesis/B-cell maturation → immune deficiency (Drosophila + patient data). 5e. (Branch) Dysregulated type I interferon signaling produces painful chilblain-like skin lesions.
The combined developmental and signaling defects manifest as the LWS clinical phenotype; variant position on the severity gradient determines whether the outcome is mild (LWS), intermediate (RS), or severe/lethal (MOPD1).

Upstream vs downstream: Steps 1–3 (variant → U4atac → minor-spliceosome failure → minor-intron retention) are upstream and shared across the entire spectrum. Steps 5a–5e are downstream, tissue-specific consequences.

Ontology suggestions: - GO biological process: mRNA splicing via spliceosome (GO:0000398), cell cycle (GO:0007049), neural progenitor proliferation, JAK-STAT signaling (GO:0007259), type I interferon signaling (GO:0060337), cilium assembly (GO:0060271). - Reactome: minor (U12-dependent) spliceosome pathway. - CL cell types: radial glial cell (CL:0000681), chondrocyte (CL:0000138), B cell (CL:0000236), rod (CL:0000604) / cone (CL:0000573) photoreceptor. - Subcellular (GO CC): spliceosomal complex (GO:0005681), nucleus/nuclear speckle; cilium (GO:0005929).

7. Anatomical Structures Affected

Skeletal system (UBERON:0001434): epiphyses (UBERON:0002515), long bones, joints — multiple epiphyseal dysplasia, short stature.
Nervous system / brain (UBERON:0000955): microcephaly, cerebral anomalies; cerebral cortex (UBERON:0000956) and radial glia affected.
Eye (UBERON:0000970): retina (UBERON:0000966) — rod-cone dystrophy; oculomotor system — nystagmus.
Immune/hematopoietic system (UBERON:0002405): B-lymphocyte compartment.
Skin (UBERON:0002097): chilblain-like lesions, often acral/bilateral.
Lateralization: skeletal and retinal involvement are characteristically bilateral/symmetric.

8. Temporal Development

Onset: Congenital/prenatal for growth and microcephaly (intrauterine growth restriction in severe cases); skeletal dysplasia and nystagmus apparent in infancy/childhood.
Course: Largely static for structural/developmental features, but progressive for the retinal dystrophy (progressive visual loss on follow-up) and episodic for chilblain-like skin lesions.
Duration: Chronic/lifelong. In LWS (mild end), lifespan is not markedly curtailed; by contrast MOPD1 is frequently lethal in infancy/early childhood.
Critical period: Fetal/early-postnatal neurodevelopment (radial glial proliferation window) is the key vulnerability period; no established intervention window exists.

9. Inheritance and Population

Inheritance: Autosomal recessive (PMID: 3706411); recurrence risk 25% per pregnancy for carrier couples.
Penetrance/expressivity: High penetrance for biallelic pathogenic genotypes, but highly variable expressivity governed by variant position and allele combination.
Epidemiology: Ultra-rare; only a few dozen molecularly confirmed RNU4ATAC-opathy patients worldwide (60 in the largest cohort). No formal prevalence/incidence estimate.
Sex ratio: No sex predilection (autosomal). Consanguinity elevates risk via homozygosity. No well-defined founder effects, though recurrent hotspot variants (e.g., n.51G>A) exist. Carrier frequency not reliably established.

10. Diagnostics

Genetic testing is definitive. Because RNU4ATAC is non-coding and single-exon, protein/splice predictors do not apply and the gene is missed by many exome kits. Recommended approach: whole-genome sequencing or targeted RNU4ATAC Sanger sequencing, especially when WES is negative in a clinically suggestive patient (PMID: 37666272; PMID: 29370840).
Functional biomarker: RNA-seq demonstrating minor-intron retention and a cellular minor-intron splicing reporter assay provide functional pathogenicity evidence and enable VUS reclassification (PMID: 42322193; PMID: 32628740).
Imaging: Skeletal survey (epiphyseal dysplasia), brain MRI (microcephaly/cerebral anomalies); ERG for retinal dystrophy (uniformly abnormal) (PMID: 37225827).
Immunology: Immunoglobulin levels and lymphocyte/B-cell subset quantification (PMID: 38837402).
CMA/karyotype: Characteristically normal (do not detect RNU4ATAC point variants).
Differential diagnosis: Other multiple epiphyseal dysplasias; other primordial dwarfisms, importantly PCNT-related MOPD II (distinguished by aneurysm/Moyamoya risk, PMID: 37234811); and within-gene RS/MOPD1.

11. Outcome / Prognosis

Survival: In LWS (mild end) life expectancy is relatively preserved; the severe MOPD1 end is frequently lethal in infancy/early childhood. No LWS-specific mortality statistics exist.
Morbidity: Driven by short stature/skeletal limitation, progressive visual impairment, cognitive impairment, and infection susceptibility.
Prognostic factors: Variant position and allele combination (severity gradient); degree of immune deficiency (infection risk) and retinal dystrophy (visual prognosis).
Complications: Recurrent infections (immune deficiency), progressive visual loss; non-ischemic cardiomyopathy reported at the RS end (PMID: 37666272).

12. Treatment

No disease-modifying or curative therapy exists; management is supportive and multidisciplinary: - Immunoglobulin replacement / infection prophylaxis for antibody deficiency (NCIT: Immunoglobulin Therapy). - Ophthalmologic surveillance and low-vision support for retinal dystrophy/nystagmus. - Orthopedic/skeletal management and physical therapy for epiphyseal dysplasia/short stature. - Developmental/educational support for delay/intellectual disability. - Dermatologic management of chilblain-like lesions (type I interferon involvement suggests a theoretical rationale for immunomodulation, but this is investigational). - Experimental: No approved gene/RNA therapies; the minor-intron-retention readout could in principle serve as a pharmacodynamic biomarker for future splice-modulating approaches. No registered disease-specific clinical trials identified.

13. Prevention

Genetic counseling for 25% recurrence risk; carrier testing of at-risk relatives (cascade testing).
Prenatal diagnosis / preimplantation genetic testing feasible once familial variants are known — prenatal diagnosis has been reported for a subsequent pregnancy in an affected family (PMID: 29370840).
Tertiary prevention: infection prophylaxis, vision monitoring, developmental intervention.
No primary prevention (not environmentally modifiable); not vaccine-preventable.

14. Other Species / Natural Disease

No naturally occurring companion-animal/wildlife disease ortholog is catalogued (no OMIA entry for LWS specifically).
RNU4ATAC/minor-spliceosome components are deeply evolutionarily conserved (present from Drosophila to mammals), enabling cross-species modeling. Orthologous minor-spliceosome snRNA function is conserved in mouse and zebrafish.
No zoonotic potential (non-infectious genetic disorder).

15. Model Organisms

Model	Manipulation	Phenotype recapitulated	PMID
Mouse (cortex)	Conditional Rnu11 (U11) ablation	Microcephaly via radial glial cell-cycle defects/death	30093551
Mouse (limb)	U11 snRNA loss	Micromelia (limb skeletal dysplasia)	32665241
Drosophila	CRISPR U4atac stem-II mutant	Growth/neurodevelopmental defects, immunodeficiency, GI symptoms; JAK/STAT mis-splicing	42463491
Zebrafish	U4atac knockdown	Ciliary defects	36802443
Human patient cells	Native biallelic variants + reporter assay	Minor-intron retention (direct molecular phenotype)	26522830, 32628740

Strengths: Mouse models directly link minor-spliceosome loss to microcephaly and skeletal dysplasia; Drosophila captures the immune axis. Limitations: Most models ablate U11/Rnu11 (a different minor-spliceosome snRNA) rather than RNU4ATAC itself, and complete ablation is more severe than the hypomorphic human variants; no model specifically reproduces the mild LWS end of the spectrum.

Mechanistic Model / Interpretation

 Biallelic LoF variants in RNU4ATAC (non-coding, chr 2q14.2)
│  (variant POSITION sets severity: 5' stem-loop = severe MOPD1;
│   dispersed = mild LWS/Roifman)
▼
 Defective U4atac snRNA
▼
 Impaired U4atac/U6atac.U5 tri-snRNP → MINOR (U12-dependent) SPLICEOSOME failure
▼
 Transcriptome-wide MINOR-INTRON RETENTION (~700–800 U12 introns)   ◄── shared, upstream
│
   ┌────┼───────────────┬───────────────┬────────────────┐
   ▼    ▼               ▼               ▼                ▼
 Radial  Chondro-      Ciliary        JAK/STAT         Type I IFN
 glia    osseous       dysfunction    mis-splicing     dysregulation
 death   disruption                   (↓JAK1)
   ▼        ▼              ▼               ▼                ▼
 MICRO-  EPIPHYSEAL     ciliopathy    IMMUNE           CHILBLAIN-like
 CEPHALY DYSPLASIA /    features      DEFICIENCY       skin lesions
 + DD    SHORT STATURE                (↓B cells)

The model's central logic is that a single upstream lesion (minor-intron retention) produces a pleiotropic, multisystem phenotype because minor introns reside in functionally diverse genes. The severity gradient (LWS ↔ RS ↔ MOPD1) is explained quantitatively by how much a given variant degrades tri-snRNP assembly (FitCons-weighted, position-dependent). Tissue selectivity (why brain, skeleton, retina, and immune cells are preferentially affected) likely reflects the high proliferative/biosynthetic demand of neural and chondro-osseous progenitors and the splicing dependence of key cell-cycle and signaling transcripts.

Evidence Base

PMID	Study (abbrev.)	Role
29265708	Expanding phenotype of RNU4ATAC to LWS	Establishes biallelic RNU4ATAC as cause of LWS
30368667	LWS: RNU4ATAC association, genotype–phenotype	Supports severity-by-variant-position; defines phenotype
41808109	Phenotypic spectrum: 4 novel + reeval	Supports MOPD1→RS severity spectrum
42322193	RNU4ATAC-opathy large cohort (n=60)	Supports core features, minor-intron retention, RNA-seq reclassification
36622817	Delineating RNU4ATAC spliceosomopathy	Supports continuum (one patient spanning all three)
26522830	Roifman syndrome, minor intron splicing	Supports U4atac essential; minor-intron defect mechanism
32628740	Clinical interpretation of RNU4ATAC variants	Supports non-coding diagnostic challenge; reporter assay
30093551	Minor spliceosome inactivation → microcephaly	Supports microcephaly mechanism (mouse)
32665241	U11 loss → micromelia	Supports skeletal mechanism (mouse)
36802443	U4atac deficiency → ciliary defects	Supports ciliary branch
42463491	U4atac regulates JAK/STAT (Drosophila)	Supports immune/JAK-STAT branch
40415209	RNU4ATAC chilblain lesions, type I IFN	Supports interferon/skin branch
37225827	Retinal dystrophy in RNU4ATAC-Roifman	Supports rod-cone dystrophy phenotype
38837402	B-cell deficiency in MOPD1 twins	Supports immunodeficiency across spectrum
3706411	Nevin 1986, LWS second family	Supports historical description, AR inheritance
29370840	Chinese family, WES-negative, targeted RNU4ATAC	Supports diagnostic pitfalls, prenatal diagnosis
37666272	Roifman as non-ischemic cardiomyopathy	Supports exome-kit coverage gap; phenotypic breadth
37234811	PCNT MOPD II with aneurysm/Moyamoya	Differential: PCNT-MOPD II is distinct from RNU4ATAC disorders

Evidence spans human clinical/genetic (majority), in vitro functional (reporter assay, patient RNA-seq), and model organism (mouse, zebrafish, Drosophila) sources, providing convergent support for the minor-intron-retention mechanism.

Limitations and Knowledge Gaps

No LWS-specific epidemiology. Prevalence, incidence, carrier frequency, and sex/age distributions are unquantified given extreme rarity; most data are pooled across the RNU4ATAC-opathy spectrum.
Genotype–phenotype resolution is incomplete. The FitCons/position model explains broad severity trends but cannot yet reliably predict LWS vs RS vs MOPD1 for a novel allele combination.
Model limitations. Most animal models ablate U11/Rnu11 rather than RNU4ATAC, and use complete knockouts rather than hypomorphic alleles; no model specifically phenocopies the mild LWS end.
Tissue-selectivity unexplained. Why specific tissues (brain, skeleton, retina, B cells) are preferentially vulnerable despite a housekeeping defect remains mechanistically unresolved.
Secondary pathways (cilia, JAK/STAT, IFN) are derived partly from allelic disorders/model organisms; their contribution specifically in mild LWS is inferred, not directly demonstrated.
No natural-history or QoL data, and no therapeutic trials — management recommendations are extrapolated from case experience.

Proposed Follow-up Experiments / Actions

Establish a prospective RNU4ATAC-opathy registry capturing genotype, minor-intron-retention burden (RNA-seq), and longitudinal phenotype (growth, vision/ERG, immune function, neurodevelopment) to quantify natural history and refine genotype–phenotype prediction.
Build hypomorphic, allele-specific models (knock-in of human LWS vs MOPD1 variants in RNU4ATAC itself; mouse and/or patient iPSC-derived cerebral and chondro-osseous organoids) to directly test the position-severity model and tissue selectivity.
Standardize a quantitative minor-intron-retention assay as a clinical functional test to resolve VUS and correlate retention burden with severity (candidate severity biomarker).
Targeted-sequencing / WGS reflex testing in any microcephalic-primordial-dwarfism or multiple-epiphyseal-dysplasia patient with negative exome — raise diagnostic yield by ensuring RNU4ATAC coverage.
Pathway-directed therapeutic exploration: test whether modulating type I interferon or JAK/STAT signaling ameliorates immune/skin phenotypes, and evaluate splice-modulating small molecules/ASOs using minor-intron-retention as a pharmacodynamic endpoint.
Systematic immunologic and ophthalmologic surveillance protocols for diagnosed patients, given the demonstrated antibody deficiency and progressive rod-cone dystrophy.

Report compiled from 24 primary references spanning human clinical, in vitro functional, and model-organism evidence. Causal gene: RNU4ATAC (U4atac snRNA, minor spliceosome). Disease: Lowry-Wood syndrome, MONDO:0009191.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.4.0.

Outcome	Count
References checked	18
Resolved	18
Unresolved (possible confabulation)	0
Unverifiable	0
References weighed for topical relevance	18
On topic	12
Off topic	0

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome	Count
Terms checked	35
Resolved	33
Unresolved (possible confabulation)	0
Obsolete	0
Unverifiable	2
Terms whose name was checked	14
Terms named correctly	5
Terms named as a different term	3
Terms whose name is worth a second look	6

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

MONDO:0009191 (5 mentions) - the report calls it "MONDO"; MONDO calls it Lowry-Wood syndrome
HP:0011109 (1 mention) - the report calls it "Chilblain-like skin lesions"; HP calls it Chronic sinusitis
UBERON:0000955 (1 mention) - the report calls it "Nervous system / brain"; UBERON calls it brain

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

HP:0002656 (1 mention) - the report calls it "Multiple epiphyseal dysplasia"; HP calls it Epiphyseal dysplasia
HP:0002060 (1 mention) - the report calls it "Cerebral anomalies"; HP calls it Abnormal cerebral morphology, and lists "Cerebral lesion" among its other names
GO:0000398 (1 mention) - the report calls it "GO biological process: mRNA splicing via spliceosome"; GO calls it mRNA splicing, via spliceosome, and lists "nuclear mRNA splicing, via spliceosome" among its other names
CL:0000681 (1 mention) - the report calls it "CL cell types: radial glial cell"; CL calls it radial glial cell
UBERON:0002405 (1 mention) - the report calls it "Immune/hematopoietic system"; UBERON calls it immune system
UBERON:0002097 (1 mention) - the report calls it "Skin"; UBERON calls it skin of body, and lists "skin" among its other names

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.

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Genetic Associations

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Diagnosis

Prevalence

Differential Diagnoses

Animal Models

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References & Deep Research

References

Deep Research

Lowry-Wood Syndrome (MONDO:0009191): A Comprehensive Disease Characteristics Report

Summary

Key Findings

Finding 1 — LWS is caused by biallelic variants in the non-coding minor-spliceosome gene RNU4ATAC

Finding 2 — RNU4ATAC disorders form a severity spectrum governed by variant location, with LWS the mildest

Finding 3 — Core clinical phenotype: multiple epiphyseal dysplasia, microcephaly, short stature, developmental delay, and eye involvement

Finding 4 — Mechanism: defective U4atac impairs the minor spliceosome, causing transcriptome-wide minor (U12-type) intron retention

Finding 5 — Secondary mechanisms: ciliary dysfunction, dysregulated JAK/STAT signaling, and type I interferon activation

Finding 6 — Immunodeficiency and progressive retinal dystrophy are recurrent, management-relevant features

Finding 7 — LWS is an autosomal recessive disorder, first described by Lowry and Wood (1975), and is ultra-rare

Finding 8 — Animal models recapitulate key features: minor-spliceosome loss causes microcephaly and limb micromelia

Finding 9 — Diagnosis requires sequencing the non-coding RNU4ATAC exon; variants are frequently missed, and RNA-seq aids classification

Finding 10 — RNU4ATAC disorders are molecularly and clinically distinct from PCNT-related MOPD type II

Detailed Report by Section

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

Mechanistic Model / Interpretation

Evidence Base

Limitations and Knowledge Gaps

Proposed Follow-up Experiments / Actions

Artifacts

Reference Validation

Term Validation

Terms the report names something else

Terms whose name is worth a second look

Prefixes with no resolver