Molecular Genomic Autopsy　― Clues to Preventing Further Tragedy? ―

Sudden cardiac death (SCD) is defined as a sudden and unexpected natural death of cardiac origin. An overall SCD incidence rate of 15–159/100,000 per year has been reported.¹ This tragedy naturally provokes the bereaved family members to ask “Why did this happen and what risks could apply to other family members?” However, the autopsy findings in up to one-third of cases of sudden death are inconclusive.² Essentially, when no underlying anatomical or toxicological cause of death is identified with autopsy, the death is diagnosed as lethal arrhythmic attack. According to a number of previous studies, the option to perform a “molecular genomic autopsy” in which the cause of death is clarified by postmortem genetic testing is very important and has been already mentioned in international guidelines or statements.^1,3,4

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In this issue of the Journal, Hata et al report a study of postmortem genetic testing with whole-exome sequencing for 10 autopsy cases of idiopathic bradyarrhythmia.⁵ Although genetic investigation of idiopathic bradyarrhythmia has been limited so far, their study clearly demonstrated evidence that genetic factors considerably contribute to its development.

As early as 2007, Tester et al performed the first postmortem genetic investigation of long QT syndrome-associated mutations in 49 cases (average age at death; 14.2 years) of autopsy-negative sudden unexplained death, and reported that over one-third of decedents harbored a putative cardiac channel mutation.⁶ The advent of high throughput next-generation sequencing has accelerated the research on “molecular genomic autopsy” in the past decade. To date, there have been many studies showing that the postmortem genetic testing is an effective approach for detecting potential pathogenic variants in SCD cases (summarized in the Table).^7–14 Based on the American College of Medical Genetics and Genomics guidelines for the interpretation of sequence variants, very rare non-synonymous variants identified in the deceased are classified as pathogenic, likely pathogenic or a variant of uncertain significance (VUS).¹⁵ When a pathogenic or likely pathogenic variant is congruent with the autopsy findings including “the heart without structural abnormality”, that is considered as a clinically actionable variant, which should immediately prompt the clinician to perform variant-specific cascade genetic screening in all first-degree relatives of the deceased. Thus, the identification of the genetic cause of SCD in the deceased provides a rational explanation of a clear cause of death to the family and facilitates further cascade genetic screening for relatives, enabling preventive measures specifically for relatives bearing the SCD-causing gene variant in order to reduce the risk of another SCD.

Table. Previous Reports of Postmortem Genetic Testing

Publication year	Country	No. of analyzed cases	No. of genes searched for variants	Rarity threshold (MAF) used in the study	Findings
20167	Australia, New Zealand	113	59	0.001	Clinically relevant cardiac gene mutation was identified in 27% of unexplained SCD cases
20168	UK, Denmark	59	135	0.0002	Very rare (<0.02%) or novel non-sense candidate mutations and previously published rare (0.02–0.5%) candidate mutations were identified in 12% and 17% of SADS cases
20179	New Zealand, Denmark, UK, Netherlands	302	77	0.0001	Clinically actionable P/LP variant was identified in 13% of the SADS cases
201710	Germany	10	174	0.0005	Evidence for a genetic disposition was found in 80% (30%; pathogenic mutation, 50%; VUS) of SUD cases
201811	USA	25	99	0.00005	Six P/LP variants in 4 SUD cases were congruent with the phenotypic findings at autopsy and reported to family members
201812	Finland	96	174	0.01	P/LP variants and VUS were found in 10% and 17% of SCD (PMF) cases, respectively
202013	Netherlands, UK, Canada, New Zealand, Singapore	57	77	0.0001	P/LP variants were detected in 3% of SCD cases with non-specific autopsy findings, vs. 32% of SCD cases with diagnostic autopsy findings of cardiomyopathy
202114	USA	103	148	0.002	P/LP variants were detected in 13% of sudden death cases and younger decedents had a higher burden of P/LP variants and select VUS

MAF, minor allele frequency; P/LP, pathogenic or likely pathogenic; PMF, primary myocardial fibrosis; SADS, sudden arrhythmic death syndrome; SCD, sudden cardiac death; SUD, sudden unexplained death; VUS, variant of uncertain significance.

In this way, the judgment of a molecular genomic autopsy of a SCD victim will have profound effects for the bereaved relatives, but proper adjudication of the SCD-causing gene variant can be practically challenging. Shanks et al struck at the heart of the matter: “The goal of these investigative studies is to provide closure to families surrounding the loss of their loved one, but perhaps the only thing worse than no answer is to give a false answer prematurely”.¹¹ The stringency of variant filtering is likely to be influenced by the rarity threshold set according to the genomic database of variant frequency in the general population. In the variant interpretation, it is crucial that the variant identified in the SCD victim is correctly designated as a pathogenic/likely pathogenic variant or a VUS. Erroneously or prematurely adjudicating equivocal variants as pathogenic has the potential to cause harm to the bereaved family members.¹¹ Also, how to deal with a VUS identified in the decedent is a big question to be answered. Judging from the genomic evidence that VUS in cardiac genes are more frequently identified in SCD victims than sex- and ancestry-matched controls without a cardiac diagnosis,¹⁴ even a VUS may have a significant effect on clinical phenotype, which remains to be elucidated. The substantial number of VUS highlights the necessity for further standardizing of the adjudication of putative pathogenic variants. Taken together, establishment of a reference database of genetic variants and improvement in variant interpretation will be essential for efficient and comprehensive genetic assessment following molecular genomic autopsy.

All previous publications on molecular genomic autopsy have been from either Europe or the USA. Generally, there are racial and ethnic differences in genetic architecture, including the distribution of disease-causing genetic variants. Given that, Hata et al’s paper is a precious report from Japan on postmortem pathological and genetic findings in a series of autopsy cases, contributing to foundational knowledge of molecular genomic autopsy. Now, in Japan, accumulation of such genetic evidence is needed to realize the molecular genomic autopsy of SCD victims and prevent another SCD among the bereaved family members.

Funding / Conflicts of Interest

None.

Disclosures

H.M. is a member of Circulation Journal’s Editorial Team.

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