Intellectual disability
Gene: FAM50A

FAM50A (family with sequence similarity 50 member A)
EnsemblGeneIds (GRCh38): ENSG00000071859
EnsemblGeneIds (GRCh37): ENSG00000071859
OMIM: 300453, Gene2Phenotype
FAM50A is in 2 panels

3 reviews

Sarah Leigh (Genomics England Curator)

The rating of this gene has been updated following NHS Genomic Medicine Service approval.
Created: 9 Mar 2022, 3:40 p.m. | Last Modified: 9 Mar 2022, 3:40 p.m.

Panel Version: 3.1510

Created: 9 Mar 2022, 3:40 p.m.
Last Modified: 9 Mar 2022, 3:40 p.m.
Panel version: 3.1510

Arina Puzriakova (Genomics England Curator)

Comment on list classification: New gene added by Konstantinos Varvagiannis. Based on the evidence provided in PMID:32703943, this gene should be promoted to Green at the next GMS panel update (added 'for-review' tag) - 6 individuals from 5 families, all exhibiting GDD/ID as the common presenting feature.
Created: 19 Nov 2020, 2:30 p.m. | Last Modified: 19 Nov 2020, 2:30 p.m.

Panel Version: 3.552

Created: 19 Nov 2020, 2:30 p.m.
Last Modified: 19 Nov 2020, 2:30 p.m.
Panel version: 3.552

Konstantinos Varvagiannis (Other)

Green List (high evidence)

Lee et al (2020 - PMID: 32703943) provide evidence that Armfield X-Linked intellectual disability syndrome is caused by monoallelic FAM50A pathogenic variants. The current review is based only on this reference.

The authors provide clinical details on 6 affected individuals from 5 families.

Features included postnatal growth delay, DD and ID (6/6 - also evident for those without formal IQ assesment), seizures (3/6 from 2 families), prominent forehead with presence of other facial features and variable head circumference (5th to >97th %le), ocular anomalies (5/6 - strabismus/nystagmus/Axenfeld-Rieger), cardiac (3/6 - ASD/Fallot) and genitourinary anomalies (3/6).

In the first of these families (Armfield et al 1999 - PMID: 10398235), linkage analysis followed by additional studies (Sanger, NGS of 718 genes on chrX, X-exome NGS - several refs provided) allowed the identification of a FAM50A variant. Variants in other families were identified by singleton (1 fam) or trio-ES (3 fam).

In affected individuals from 3 families, the variant had occurred de novo. Carrier females in the other families were unaffected (based on pedigrees and/or the original publication). XCI was rather biased in most obligate carrier females from the 1st family (although this ranged from 95:5 to 60:40).

Missense variants were reported in all affected subjects incl. Trp206Gly, Asp255Gly, Asp255Asn (dn), Glu254Gly (dn), Arg273Trp (dn) (NM_004699.3).

Previous studies have demonstrated that FAM50A has ubiquitous expression in human fetal and adult tissues (incl. brain in fetal ones).

Immunostaining suggests a nuclear localization for the protein (NIH/3T3 cells). Comparison of protein levels in LCLs from affected males and controls did not demonstrate significant differences. Protein localization for 3 variants (transfection of COS-7 cells) was shown to be similar to wt.

Complementation studies in zebrafish provided evidence that the identified variants confer partial loss of function (rescue of the morpholino phenotype with co-injection of wt but not mt mRNA). The zebrafish ko model seemed to recapitulate the abnormal development of cephalic structures and was indicative of diminished/defective neurogenesis. Transcriptional dysregulation was demonstrated in zebrafish (altered levels and mis-splicing). Upregulation of spliceosome effectors was demonstrated in ko zebrafish.

Similarly, mRNA expression and splicing defects were demonstrated in LCLs from affected individuals. FAM50A pulldown followed by mass spectrometry in transfected HEK293T cells demonstrated enrichment of binding proteins involved in RNA processing and co-immunoprecipitation assays (transfected U-87 cells) suggested that FAM50A interacts with spliceosome U5 and C-complex proteins.

Overall aberrant spliceosome C-complex function is suggested as the underlying pathogenetic mechanism.

Several other neurodevelopmental syndromes are caused by variants in genes encoding C-complex affiliated proteins (incl. EFTUD2, EIF4A3, THOC2, etc.).

Please consider inclusion in the ID panel with green rating and epilepsy panel with amber (seizures in individuals from 2 families).
Sources: Literature
Created: 8 Aug 2020, 11:26 a.m.

Mode of inheritance
X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)

Phenotypes
Mental retardation syndrome, X-linked, Armfield type (MIM #300261)

Publications

32703943

Created: 8 Aug 2020, 11:26 a.m.

Panel version: 3.239

Details

Mode of Inheritance

X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)

Sources

Expert Review Green

Phenotypes

Mental retardation syndrome, X-linked, Armfield type, OMIM:300261
Armfield syndrome, MONDO:0010284

OMIM

300453

Clinvar variants

Variants in FAM50A

Penetrance

unknown

Publications

32703943

Panels with this gene