ClinVar Genomic variation as it relates to human health

The TCAP Glu13del variant has been previously identified in multiple HCM and DCM patients (Bos JM, et al., 2006; Perrot A, et al., 2006; Marziliano N, et al., 2006; Anderson PS, et al., 2009; Hirtle-Lewis M, et al., 2013; Pugh TJ, et al., 2014), however it has also been identified control cohorts at an allele frequency of up to 0.5% (Perrot A, et al., 2006; Marziliano N, et al., 2006; Anderson PS, et al., 2009). In vitro functional evaluations have shown that the TCAP Glu13del variant causes improper formation of telethonin β-hairpin structure necessary for titin binding, that may in fact be harmless (Knoll R, et al., 2011). The variant is present in the Exome Aggregation Consortium dataset (MAF= 0.00095; http://exac.broadinstitute.org/). We identified this variant in 3 HCM probands. In one of these families both the proband and an affected family member also carried a second pathogenic variant (MYBPC3 p.Pro955Argfs*95). In another family it was found to cosegregate in two affected family members, but did not segregate to a third affected family member. In summary, based on identification of the variant in controls, high allele frequency, as well as the lack of segregation in our family, we classify TCAP Glu13del as a "benign" variant.

This alteration is classified as likely benign based on a combination of the following: seen in unaffected individuals, population frequency, intact protein function, lack of segregation with disease, co-occurrence, RNA analysis, in silico models, amino acid conservation, lack of disease association in case-control studies, and/or the mechanism of disease or impacted region is inconsistent with a known cause of pathogenicity.

The variant is found in DCM,CARDIOMYOPATHY panel(s).

Variant summary: TCAP c.37_39delGAG (p.Glu13del) results in an in-frame deletion that is predicted to remove one amino acids from the encoded protein. The variant allele was found at a frequency of 0.001 in 276952 control chromosomes in the gnomAD database, including 1 homozygotes. The observed variant frequency is approximately 40-fold of the estimated maximal expected allele frequency for a pathogenic variant in TCAP causing Cardiomyopathy phenotype (2.5e-05), strongly suggesting that the variant is benign. The variant, c.37_39delGAG, has been reported in the literature in individuals affected with Cardiomyopathy as well as in controls (Marziliano_2006, Perrot_2006). In vitro studies have shown the variant to result in the inability to bind the titin N-terminus due to the loss of proper formation of the telethonin B-hairpin structure, which the authors state may in fact be harmless (Knoll_2011). Nine 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. One cardiology center (via ClinVar), reports the variant in HCM family members who also carried a pathogenic MYBPC3 variant, and in another family, the variant did not segregate with disease in all affected family members. Based on the evidence outlined above, the variant was classified as benign.

The p.Glu13del variant in TCAP is classified as benign because it has been identified in 0.4% (43/10340) of Ashkenazi Jewish chromosomes (including one homozygote) and in 0.1% (182/128862) of European chromosomes by gnomAD (http://gnomad.broadinstitute.org). ACMG/AMP Criteria applied: BA1.

Criteria: BS1, BS2, PM4

TCAP: PM4:Supporting, BS2