ClinVar Genomic variation as it relates to human health

Variant summary: CAPN3 c.133G>A (p.Ala45Thr) results in a non-conservative amino acid change in the encoded protein sequence. Four of five in-silico tools predict a damaging effect of the variant on protein function. The variant allele was found at a frequency of 1.2e-05 in 251398 control chromosomes (gnomAD). c.133G>A has been reported in the literature as a biallelic genotype in multiple individuals affected with Limb-Girdle Muscular Dystrophy, Autosomal Recessive (e.g. Chrobakova_2004, Groen_2007). These data indicate that the variant is very likely to be associated with disease. 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: 15351423, 18055493). Four clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar after 2014 and all classified the variant as pathogenic (n=2)/likely pathogenic (n=2). Based on the evidence outlined above, the variant was classified as pathogenic.

This sequence change replaces alanine, which is neutral and non-polar, with threonine, which is neutral and polar, at codon 45 of the CAPN3 protein (p.Ala45Thr). This variant is present in population databases (rs774048743, gnomAD 0.003%). This missense change has been observed in individual(s) with autosomal recessive limb-girdle muscular dystrophy (PMID: 15351423, 16650086, 18055493, 19556129). ClinVar contains an entry for this variant (Variation ID: 217148). Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) performed at Invitae indicates that this missense variant is expected to disrupt CAPN3 protein function with a positive predictive value of 95%. For these reasons, this variant has been classified as Pathogenic.

Published functional studies demonstrate no detectable protein in the muscle tissue of a patient homozygous for this variant (PMID: 15351423); Identified in patients with limb-girdle muscular dystrophy who also harbored a second variant in CAPN3, however, it is unknown if these variants were on the same (in cis) or opposite (in trans) CAPN3 allele (PMID: 16650086, 19556129); Not observed at a significant frequency in large population cohorts (gnomAD); In silico analysis supports that this missense variant does not alter protein structure/function; This variant is associated with the following publications: (PMID: 19556129, 16372320, 16650086, 17157502, 18055493, 37526466, 15351423)