ClinVar Genomic variation as it relates to human health

The c.9569C>T variant (NM_022124.6(CDH23):c.9569C>T (p.Ala3190Val)) in CDH23 is a missense variant predicted to cause substitution of alanine by valine at amino acid 3190 (p.Ala3190Val). The highest minor allele frequency in gnomAD v4.0.0 is 694/1179698 alleles (0.0005517), in the European (non-Finnish) population (no population codes met). This variant has been observed in a homozygous state in one parent reported to have no features of Usher syndrome (BS2; Invitae internal data; ClinVar SCV001110059.2). The computational predictor REVEL gives a score of 0.836, which is above the Hearing Loss VCEP threshold of 0.7, evidence that correlates with impact to CDH23 function (PP3). The variant was found in a compound heterozygous state with a deletion of exon 29, a variant which was not able to be confirmed by aCGH (PMID: 25404053). The variant was also found in an unknown phase with p.Arg3206Cys (c.9616C>T), a variant of uncertain significance, in an affected patient with nonsyndromic hearing loss (PMID: 27068579; PM3 not met). In summary, the clinical significance of this variant is uncertain. ACMG/AMP criteria applied, as specified by the ClinGen Hearing Loss Expert Panel: BS2, PP3 (Version 2; 11/15/2023).

The CDH23 c.9569C>T (p.Ala3190Val) missense variant has been reported in two studies in which it is identified in a compound heterozygous state in two individuals, one with a diagnosis of Usher syndrome and one with autosomal recessive nonsyndromic hearing loss (Aparisi et al. 2014; Sommen et al. 2016). Control data are unavailable for this variant, which is reported at a frequency of 0.00047 in the European (non-Finnish) population of the Exome Aggregation Consortium. The evidence for this variant is limited. Based on the evidence, the p.Ala3190Val variant is classified as a variant of unknown significance but suspicious for pathogenicity for CDH23-related disorders. This variant was observed by ICSL as part of a predisposition screen in an ostensibly healthy population.

The p.Ala3190Val variant in CDH23 has been reported in 1 individual with Usher s yndrome who also had a duplication of exon 29 in CDH23 that is of uncertain sign ificance (Aparisi 2014), and in 1 individual with hearing loss who also had the p.Arg3206Cys variant of uncertain significance in CDH23 (Sommen 2016). The p.Ala 3190Val variant has also been identified by our laboratory in the heterozygous s tate in 3 individuals with hearing loss; however, a variant affecting the remain ing copy of CDH23 was not identified in any of these individuals. This variant h as been identified in 0.08% (8/10122) of Ashkenazi Jewish chromosomes and 0.05% (64/126200) European chromosomes by Genome Aggregation Database (gnomAD, http:// gnomad.broadinstitute.org; dbSNP rs111033536). Although this variant has been se en in the general population, its frequency is not high enough to rule out a pat hogenic role. Computational prediction tools and conservation analyses suggest t hat this variant may impact the protein, though this information is not predicti ve enough to determine pathogenicity. In summary, the clinical significance of t he p.Ala3190Val variant is uncertain.

Variant summary: CDH23 c.9569C>T (p.Ala3190Val) results in a non-conservative amino acid change in the encoded protein sequence. Five of five in-silico tools predict a damaging effect of the variant on protein function. The variant allele was found at a frequency of 0.00034 in 247998 control chromosomes (gnomAD). This frequency is not significantly higher than estimated for a pathogenic variant in CDH23 causing Usher Syndrome (0.00034 vs 0.0032), allowing no conclusion about variant significance. c.9569C>T has been reported in the literature in individuals with hearing loss (e.g., Aparisi_2014, Sommen_2016, Clabout_2022), however without strong evidence of causality in all cases (e.g., lack of a second confirmed CDH23 allele and/or segregation/phase not determined). This variant was also listed as an expert curated classification of "likely pathogenic" in the Deafness Variation Database (DVD) (e.g., Azaiez_2018) and cited by others (e.g., Chen_2019). These reports therefore do not provide unequivocal conclusions about association of the variant with Usher Syndrome. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. The following publications have been ascertained in the context of this evaluation (PMID: 25404053, 30245029, 27068579, 36672845, 31445392). Eight clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar after 2014 without evidence for independent evaluation. Multiple laboratories reported the variant with conflicting assessments (VUS, n=6; Likely pathogenic, n=1; Benign, n=1). Based on the evidence outlined above, the variant was classified as uncertain significance.

PS1_Moderate, PM2_Moderate, PP3_Supporting

Identified in a patient with nonsyndromic hearing loss, along with a second variant with unknown phase in published literature (PMID: 27068579); In silico analysis indicates that this missense variant does not alter protein structure/function; This variant is associated with the following publications: (PMID: 30245029, 32387678, 31445392, 36672845, 27068579, 25404053)

CDH23: PP3

The CDH23 c.9569C>T variant is predicted to result in the amino acid substitution p.Ala3190Val. This variant has been reported in the presumed compound heterozygous state with a duplication of exon 29 (that was not confirmed by orthogonal method) in an individual with Usher syndrome (Aparisi et al. 2014. PubMed ID: 25404053). It has also been reported together with another variant of uncertain significance in CDH23 in patient with hearing loss (Table S2, Sommen et al. 2016. PubMed ID: 27068579) and in the heterozygous state without a second disease-causing variant in another individual with non-syndromic hearing loss (NSHL) (Table A2, Clabout et al. 2022. PubMed ID: 36672845). Of note, this variant has also been observed in the homozygous state in a patient tested for Usher syndrome at PreventionGenetics who was also homozygous for a protein-truncating variant in the PCDH15 gene (internal data). This variant is reported in 0.068% of alleles in individuals of Ashkenazi Jewish descent in gnomAD. At this time, the clinical significance of this variant is uncertain due to the absence of conclusive functional and genetic evidence.