A Splice Variant of the MYH7 Gene Is Causative in a Family with Isolated Left Ventricular Noncompaction Cardiomyopathy.

Variants of the MYH7 gene have been associated with a number of primary cardiac conditions, including left ventricular noncompaction cardiomyopathy (LVNC). Most cases of MYH7-related diseases are associated with such variant types as missense substitutions and in-frame indels. Thus, truncating variants in MYH7 (MYH7tv) and associated mechanism of haploinsufficiency are usually considered not pathogenic in these disorders. However, recent large-scale studies demonstrated evidence of the significance of MYH7tv for LVNC and gave rise to an assumption that haploinsufficiency may be the causal mechanism for LVNC. In this article, we present a family with isolated LVNC and a heterozygous splice variant of the MYH7 gene, analyze possible consequences of this variant and conclude that not all variants that are predicted truncating really act through haploinsufficiency. This study can highlight the importance of a precise assessment of MYH7 splicing variants and their participation in the development of LVNC.

Allelic Dropout Is a Common Phenomenon That Reduces the Diagnostic Yield of PCR-Based Sequencing of Targeted Gene Panels.

Primary cardiomyopathies (CMPs) are monogenic but multi-allelic disorders with dozens of genes involved in pathogenesis. The implementation of next-generation sequencing (NGS) approaches has resulted in more time- and cost-efficient DNA diagnostics of cardiomyopathies. However, the diagnostic yield of genetic testing for each subtype of CMP fails to exceed 60%. The aim of this study was to demonstrate that allelic dropout (ADO) is a common phenomenon that reduces the diagnostic yield in primary cardiomyopathy genetic testing based on targeted gene panels assayed on the Ion Torrent platform. We performed mutational screening with three custom targeted gene panels based on sets of oligoprimers designed automatically using AmpliSeq Designer® containing 1049 primer pairs for 37 genes with a total length of 153 kb. DNA samples from 232 patients were screened with at least one of these targeted gene panels. We detected six ADO events in both IonTorrent PGM (three cases) and capillary Sanger sequencing (three cases) data, identifying ADO-causing variants in all cases. All ADO events occurred due to common or rare single nucleotide variants (SNVs) in the oligoprimer binding sites and were detected because of the presence of "marker" SNVs in the target DNA fragment. We ultimately identified that PCR-based NGS involves a risk of ADO that necessitates the use of Sanger sequencing to validate NGS results. We assume that oligoprimer design without ADO data affects the amplification efficiency of up to 0.77% of amplicons.