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Mendeliome v1.3735 MT-ATP8 Zornitza Stark commented on gene: MT-ATP8: LIMITED by ClinGen. Three variants (m.8403T>C, m.8411A>G, m.8424T>C) have been reported in three individuals. Age of onset varied from birth to the 30s. Clinical features included muscle weakness, wasting, and cramping; dysarthria, headache, periodic paralysis, seizures, mood disorder, neuropathy, pancreatitis, diarrhoea, and weight loss. Brain imaging revealed cerebellar atrophy; lactate was elevated. The gene-disease relationship is also supported by a biochemical function (complex V subunit) shared with other genes associated with primary mitochondrial disease, functional alteration in non-patient cells, and model organisms.
Mendeliome v1.3520 RRP12 Catherine Dalzell gene: RRP12 was added
gene: RRP12 was added to Mendeliome. Sources: Literature
Mode of inheritance for gene: RRP12 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: RRP12 were set to PMID: 41059649
Phenotypes for gene: RRP12 were set to Brain calcifications
Penetrance for gene: RRP12 were set to unknown
Mode of pathogenicity for gene: RRP12 was set to Other
Review for gene: RRP12 was set to AMBER
Added comment: Variants: 5 individuals from 3 unrelated families with homozygous RRP12 variants (3 different variants, 2 consanguineous families with same variant, 2 siblings with same variant).

Phenotype: all individuals had brain calcifications (varying distribution, severity and age of onset). The patients from the two consanguineous families both had infantile-onset generalised dystonia, spasticity and severe speech impairment with widespread brain calcifications. One also had microcephaly, seizures and a cataract whilst the other had mild thrombocytopenia. The two siblings had psychiatric symptoms (one bipolar disease and one anxiety) with marked, bilateral symmetric calcifications. One also had cerebellar ataxia, choreic movements, cognitive impairment and subtle Parkinsonism whilst the other had chronic tinnitus. The final individual had dizziness and only faint bilateral lenticular calcifications.

Functional data: a statistically significant reduction in RRP12 protein levels in probands’ fibroblasts compared to controls was demonstrated. rrp12 knockdown in zebrafish embryos demonstrated reduced survival (50% survival at 2 days and maximum survival of 6 days compared to 100% survival at 6 days in controls). Phenotype abnormalities (delayed development and crimping) were also seen in the rrp12 knockdown embryos. Functional studies support a possible LoF mechanism.
Sources: Literature
Mendeliome v1.2949 DDX39A Krithika Murali gene: DDX39A was added
gene: DDX39A was added to Mendeliome. Sources: Literature
Mode of inheritance for gene: DDX39A was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: DDX39A were set to PMID: 40726340
Phenotypes for gene: DDX39A were set to Neurodevelopmental disorder, MONDO:0700092, DDX39A-related
Review for gene: DDX39A was set to RED
Added comment: PMID: 40726340 Ahmed et al 2025 (Clinical Genetics) report a 7 month old F with GDD, seizures, microcephaly, hypotonia, corpus callosum thinning and homozygous missense variant (p.Lys137Gln) in DDX39A on trio WES with both non-consanguineous parents confirmed to be heterozygous carriers. DDX39A is involved in mRNA splicing and export. Patient-derived fibroblast studies showed that mutant protein resulted in aberrant nuclear clumping and failure to interact with the TREX complex.

Of note, closely-related paralogue DDX39B is also a component of the TREX complex and has a definitive monoallelic association with neurodevelopmental disorder.
Sources: Literature
Mendeliome v1.1787 AGTR2 Zornitza Stark changed review comment from: Variants in AGTR2 have been reported in individuals presenting various neurodevelopmental phenotypes, including intellectual disability, autistic features, epileptic seizures, speech delay, restlessness, and hyperactivity, as early as 2002. Per criteria outlined by the ClinGen Lumping and Splitting Working Group, we found no difference in molecular mechanism, inheritance pattern, or phenotypic variability. Therefore, for the purposes of this curation, all of these features have been lumped into one disease entity, X-linked complex neurodevelopmental disorder. Although eight unique variants, including missense and truncating, have been reported in affected humans, the majority (six) have been ruled out from disease-causality based on high frequency in control populations (Piton et al., PMID 23871722), occurrence in unaffected males (Erdmann et al., PMID 14722754), non-segregation within a family (Bienvenu et al., PMID 12746399), and lack of enrichment in patients in a case-control study (Huang et al., PMID 16283672). Given that the two remaining variants are missense with no supporting functional evidence, and AGTR2 was the only gene sequenced in each case, the ClinGen Intellectual Disability and Autism Working Group recommended awarding 0 points for these variants. There are two AGTR2 mouse models which collectively show altered neuronal spine morphology, spatial memory impairment, delayed learning, and reduced exploratory behavior (PMIDs 18335189 and 7477267).
Sources: Expert Review; to: DISPUTED by ClinGen:

Variants in AGTR2 have been reported in individuals presenting various neurodevelopmental phenotypes, including intellectual disability, autistic features, epileptic seizures, speech delay, restlessness, and hyperactivity, as early as 2002. Per criteria outlined by the ClinGen Lumping and Splitting Working Group, we found no difference in molecular mechanism, inheritance pattern, or phenotypic variability. Therefore, for the purposes of this curation, all of these features have been lumped into one disease entity, X-linked complex neurodevelopmental disorder. Although eight unique variants, including missense and truncating, have been reported in affected humans, the majority (six) have been ruled out from disease-causality based on high frequency in control populations (Piton et al., PMID 23871722), occurrence in unaffected males (Erdmann et al., PMID 14722754), non-segregation within a family (Bienvenu et al., PMID 12746399), and lack of enrichment in patients in a case-control study (Huang et al., PMID 16283672). Given that the two remaining variants are missense with no supporting functional evidence, and AGTR2 was the only gene sequenced in each case, the ClinGen Intellectual Disability and Autism Working Group recommended awarding 0 points for these variants. There are two AGTR2 mouse models which collectively show altered neuronal spine morphology, spatial memory impairment, delayed learning, and reduced exploratory behavior (PMIDs 18335189 and 7477267).
Sources: Expert Review
Mendeliome v1.1787 AGTR2 Zornitza Stark gene: AGTR2 was added
gene: AGTR2 was added to Mendeliome. Sources: Expert Review
disputed tags were added to gene: AGTR2.
Mode of inheritance for gene: AGTR2 was set to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Phenotypes for gene: AGTR2 were set to X-linked complex neurodevelopmental disorder MONDO:0100148
Review for gene: AGTR2 was set to RED
Added comment: Variants in AGTR2 have been reported in individuals presenting various neurodevelopmental phenotypes, including intellectual disability, autistic features, epileptic seizures, speech delay, restlessness, and hyperactivity, as early as 2002. Per criteria outlined by the ClinGen Lumping and Splitting Working Group, we found no difference in molecular mechanism, inheritance pattern, or phenotypic variability. Therefore, for the purposes of this curation, all of these features have been lumped into one disease entity, X-linked complex neurodevelopmental disorder. Although eight unique variants, including missense and truncating, have been reported in affected humans, the majority (six) have been ruled out from disease-causality based on high frequency in control populations (Piton et al., PMID 23871722), occurrence in unaffected males (Erdmann et al., PMID 14722754), non-segregation within a family (Bienvenu et al., PMID 12746399), and lack of enrichment in patients in a case-control study (Huang et al., PMID 16283672). Given that the two remaining variants are missense with no supporting functional evidence, and AGTR2 was the only gene sequenced in each case, the ClinGen Intellectual Disability and Autism Working Group recommended awarding 0 points for these variants. There are two AGTR2 mouse models which collectively show altered neuronal spine morphology, spatial memory impairment, delayed learning, and reduced exploratory behavior (PMIDs 18335189 and 7477267).
Sources: Expert Review
Mendeliome v0.8601 CLCN3 Kristin Rigbye gene: CLCN3 was added
gene: CLCN3 was added to Mendeliome. Sources: Literature
Mode of inheritance for gene: CLCN3 was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Publications for gene: CLCN3 were set to PMID: 34186028
Phenotypes for gene: CLCN3 were set to Neurodevelopmental disorder
Mode of pathogenicity for gene: CLCN3 was set to Other
Review for gene: CLCN3 was set to GREEN
Added comment: 11 individuals reported, 9 that carried 8 different rare heterozygous missense variants in CLCN3, and 2 siblings that were homozygous for an NMD-predicted frameshift variant likely abolishing ClC-3 function. All missense variants were confirmed to be de novo in eight individuals for whom parental data was available.

The 11 individuals in the cohort share clinical features of variable severity. All 11 have GDD or ID and dysmorphic features, and a majority has mood or behavioural disorders and structural brain abnormalities:
- Structural brain abnormalities on MRI (9/11) included partial or full agenesis of the corpus callosum (6/9), disorganized cerebellar folia (4/9), delayed myelination (3/9), decreased white matter volume (3/9), pons hypoplasia (3/9), and dysmorphic dentate nuclei (3/9). Six of those with brain abnormalities also presented with seizures.
- Nine have abnormal vision, including strabismus in four and inability to fix or follow in the two with homozygous loss-of-function variants.
- Hypotonia ranging from mild to severe was reported in 7 of the 11 individuals.
- Six have mood or behavioural disorders, particularly anxiety (3/6).
- Consistent dysmorphic facial features included microcephaly, prominent forehead, hypertelorism, down-slanting palpebral fissures, full cheeks, and micrognathia.

The severity of disease in the two siblings with homozygous disruption of ClC-3 is consistent with the drastic phenotype seen in Clcn3 KO mice. The disease was more severe in two siblings carrying homozygous loss-of-function variants with the presence of GDD, absent speech, seizures, and salt and pepper fundal pigmentation in both individuals, with one deceased at 14 months of age. The siblings also had significant neuroanatomical findings including diffusely decreased white matter volume, thin corpora callosa, small hippocampi, and disorganized cerebellar folia. Supporting biallelic inheritance for LoF variants, disruption of mouse Clcn3 results in drastic neurodegeneration with loss of the hippocampus a few months after birth and early retinal degeneration. Clcn3−/− mice display severe neurodegeneration, whereas heterozygous Clcn3+/− mice appear normal.

Patch-clamp studies were used to investigate four of the missense variants. These suggested a gain of function in two variants with increased current in HEK cells, however they also showed reduced rectification of voltage and a loss of transient current, plus decreased current amplitude, glycosylation and surface expression when expressed in oocytes, and were suspected to interfere with channel gating and a negative feedback mechanism. These effects were also shown to vary depending on pH levels. The current of the remaining two variants did not differ from WT. For heterozygous missense variants, the disruption induced may be at least partially conferred to mutant/WT homodimers and mutant/ClC-4 heterodimers.

Both loss and gain of function in this gene resulted in the same phenotype.
Sources: Literature
Mendeliome v0.5724 MPI Zornitza Stark Marked gene: MPI as ready
Mendeliome v0.5724 MPI Zornitza Stark Gene: mpi has been classified as Green List (High Evidence).
Mendeliome v0.5724 MPI Zornitza Stark Phenotypes for gene: MPI were changed from to Congenital disorder of glycosylation, type Ib, MIM# 602579; MPI-CDG MONDO:0011257
Mendeliome v0.5723 MPI Zornitza Stark Publications for gene: MPI were set to
Mendeliome v0.5722 MPI Zornitza Stark Mode of inheritance for gene: MPI was changed from Unknown to BIALLELIC, autosomal or pseudoautosomal
Mendeliome v0.5721 MPI Zornitza Stark reviewed gene: MPI: Rating: GREEN; Mode of pathogenicity: None; Publications: 12414827, 9585601, 10980531, 33098580, 33204592, 32905087, 32266963, 30242110; Phenotypes: Congenital disorder of glycosylation, type Ib, MIM# 602579, MPI-CDG MONDO:0011257; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Mendeliome v0.5553 KDM4B Kristin Rigbye gene: KDM4B was added
gene: KDM4B was added to Mendeliome. Sources: Literature
Mode of inheritance for gene: KDM4B was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Publications for gene: KDM4B were set to PMID: 33232677
Phenotypes for gene: KDM4B were set to Global developmental delay, intellectual disability and neuroanatomical defects
Review for gene: KDM4B was set to GREEN
Added comment: Nine individuals with mono-allelic de novo or inherited variants in KDM4B.

All individuals presented with dysmorphic features and global developmental delay (GDD) with language and motor skills most affected. Three individuals had a history of seizures, and four had anomalies on brain imaging ranging from agenesis of the corpus callosum with hydrocephalus to cystic formations, abnormal hippocampi, and polymicrogyria.

In a knockout mouse the total brain volume was significantly reduced with decreased
size of the hippocampal dentate gyrus, partial agenesis of the corpus callosum, and ventriculomegaly.
Sources: Literature
Mendeliome v0.3784 MPIG6B Zornitza Stark Marked gene: MPIG6B as ready
Mendeliome v0.3784 MPIG6B Zornitza Stark Gene: mpig6b has been classified as Green List (High Evidence).
Mendeliome v0.3784 MPIG6B Zornitza Stark Classified gene: MPIG6B as Green List (high evidence)
Mendeliome v0.3784 MPIG6B Zornitza Stark Gene: mpig6b has been classified as Green List (High Evidence).
Mendeliome v0.3783 MPIG6B Zornitza Stark gene: MPIG6B was added
gene: MPIG6B was added to Mendeliome. Sources: Expert list
Mode of inheritance for gene: MPIG6B was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: MPIG6B were set to 31276734; 29898956; 27743390
Phenotypes for gene: MPIG6B were set to Thrombocytopenia, anemia, and myelofibrosis, MIM# 617441
Review for gene: MPIG6B was set to GREEN
Added comment: Six families reported.
Sources: Expert list
Mendeliome v0.0 MPI Zornitza Stark gene: MPI was added
gene: MPI was added to Mendeliome_VCGS. Sources: Expert Review Green,Victorian Clinical Genetics Services
Mode of inheritance for gene: MPI was set to Unknown