Genomic Triangulation and Coverage Analysis in Whole-Exome Sequencing-Based Molecular Autopsies

WEMA (Whole-Exome Molecular Autopsy) and surveillance of cardiac channelopathy and cardiomyopathy genes represents the latest molecular autopsy for sudden death in the young (SDY). To date, the majority of WEMA has been performed on the SDY case only.

We performed whole-exome sequencing and nucleotide-level coverage analysis on 28 SDY cases (18.4±7.8 years) and their parents to determine the inheritance patterns of ultrarare, nonsynonymous variants in 99 sudden death-susceptibility genes. Nonsynonymous variants were adjudicated using the American College of Medical Genetics guidelines. Overall, 17 sudden death-susceptibility gene variants were identified in 12 of 28 (43%) SDY cases. On the basis of the American College of Medical Genetics guidelines, 6 of 28 (21%) cases had a pathogenic or likely pathogenic nonsynonymous variant with 3 (50%) being de novo. Two nonsynonymous variants would not have been elevated to likely pathogenic status without knowing their de novo status. Whole-exome sequencing reached a read depth of 10× across 90% of nucleotides within sudden death-susceptibility genes in 100% of parental exomes from fresh blood draw, compared with only 82% of autopsy-sourced SDY exomes.

An SDY-parent, trio-based WEMA may be an effective way of elucidating a monogenic cause of death and bringing clarity to otherwise ambiguous variants. If other studies confirm this relatively high rate of SDY cases stemming from de novo mutations, then the WEMA should become even more cost-effective given that the decedent's first-degree relatives should only need minimal cardiological evaluation. In addition, autopsy-sourced DNA demonstrated strikingly lower whole-exome sequencing coverage than DNA from fresh blood draw.