This sequence change replaces serine, which is neutral and polar, with arginine, which is basic and polar, at codon 212 of the MYBPC3 protein (p.Ser212Arg). This variant is not present in population databases (gnomAD no frequency). This missense change has been observed in individuals with hypertrophic cardiomyopathy (PMID: 18533079, 27532257, 33782553; internal data). ClinVar contains an entry for this variant (Variation ID: 42776). An algorithm developed to predict the effect of missense changes on protein structure and function (PolyPhen-2) suggests that this variant is likely to be disruptive. Studies have shown that this missense change alters mRNA splicing and is expected to lead to the loss of protein expression (PMID: 28679633). For these reasons, this variant has been classified as Pathogenic.

The p.S212R variant (also known as c.636C>G), located in coding exon 5 of the MYBPC3 gene, results from a C to G substitution at nucleotide position 636. The serine at codon 212 is replaced by arginine, an amino acid with dissimilar properties. This variant was reported in individual(s) with features consistent with hypertrophic cardiomyopathy (HCM) (Olivotto I et al. Mayo Clin Proc, 2008 Jun;83:630-8; Alfares AA et al. Genet Med, 2015 Nov;17:880-8; Walsh R et al. Genet Med, 2017 02;19:192-203; Smith E et al. J Am Heart Assoc, 2022 05;11:e024501; Ambry internal data; external communication). This amino acid position is not well conserved in available vertebrate species. In addition, the in silico prediction for this alteration is inconclusive. This variant is considered to be rare based on population cohorts in the Genome Aggregation Database (gnomAD). Based on the majority of available evidence to date, this variant is likely to be pathogenic.

Variant classified as Uncertain Significance - Favor Pathogenic. The p.Ser212Arg variant in MYBPC3 has been reported in 1 individual with HCM (Olivotto 2008) an d was absent from large population studies. It has also been identified by our l aboratory in 2 Caucasian adults with HCM and segregated with the disease in 2 af fected relatives. Computational prediction tools and conservation analysis do no t provide strong support for or against an impact to the protein. The change to arginine (Arg) at position 212 was predicted to be benign using a computational tool clinically validated by our laboratory. This tool's benign prediction is es timated to be correct 89% of the time (Jordan 2011). However, this variant is pr edicted to create an alternative 5' splice site, and while this is not predictiv e enough to determine pathogenicity, it is consistent with the established mecha nism of disease for MYBPC3. In summary, though its clinical significance remains uncertain, its presence in multiple affected individuals, segregation with dise ase, and possible splicing impact raise suspicion that this variant may have a r ole in disease.

Not observed at significant frequency in large population cohorts (gnomAD); In silico analysis supports that this missense variant has a deleterious effect on protein structure/function; In silico splicing algorithms predict this variant results in the creation of a cryptic splice donor site upstream of the natural splice donor site for intron 5; This variant is associated with the following publications: (PMID: 18533079, 27532257, 33782553, 28679633)