Genetic variants of uncertain significance: How to match scientific rigour and standard of proof in sudden cardiac death?

In many SCD cases, in particular in pediatric age, autopsy can be completely negative and then a post-mortem genetic testing (molecular autopsy) is indicated. In NGS era finding new/rare variants is extremely frequent and, when only variants of unknown significance are found, molecular autopsy fails to find a cause of death. We describe the emblematic case of the sudden death of a 7-year-old girl. We performed a full-body micro-CT analysis, an accurate autopsy, a serum tryptase test and toxicological tests. Since the only macroscopic abnormality we found was a myocardial bridging (length: 1,1 cm, thickness: 0,5 cm) of the left anterior descending coronary artery, a molecular autopsy has been performed. NGS analysis on victim DNA detected rare variants in DPP6, MYH7, SCN2B and NOTCH1 and segregation analysis was then achieved. On the basis of ACMG/AMP (clinical) guidelines, all the found variants were classified as of unknown significance. In other words, both the macroscopic and genetic anomalies we found were of uncertain significance and then the autopsy failed to find the cause of the death. Our case raises three main discussion points: (a) economical, ethical and legal limitations of genetic investigation; (b) risk that genetic testing does not succeed in finding a certain cause of the death; (c) absence of specific guidelines to face the problem of VUS in forensic cases.

Association between leucocyte telomere length and cardiovascular disease in a large general population in the United States

Leucocyte telomere length (LTL) has been reported to be linked to ageing, cancer and cardiovascular disease (CVD). This study aimed to explore the association between LTL and CVD risk in a nationally representative sample of U.S. adults. Complex associations, including nonlinearity and interaction, were also examined. A total of 7,378 subjects from the National Health and Nutrition Examination Survey (NHANES) 1999-2002 were collected. Telomere length was detected from DNA samples and expressed as the mean T/S ratio (telomere repeats per single-copy gene). We performed multiple logistic regression models and interactive analysis to explore the associations between LTL and CVD risk by adjusting for potential confounders. We also performed a sensitivity analysis to investigate the robustness of our results. Among all participants, LTL was associated with the risk of CVD (OR = 0.79, 95% CI: 0.63~0.98, P = 0.033) in a linear manner rather than in a nonlinear manner (P = 0.874). Interaction effects of LTL with both education (P = 0.017) and hypertension (P = 0.007) were observed. Furthermore, using subgroup analyses, protective effects of LTL on CVD risk were found in females and in individuals who were college graduates or above, had serum cotinine >10 ng/ml, did not have hypertension, or had normal white blood cell levels. LTL is linearly inversely associated with CVD risk in the general population of the United States.

Mitochondrial DNA variation in sudden cardiac death: a population-based study

Cardiomyopathy and cardiac conduction defects are common manifestations of mitochondrial disease. Previous studies suggest that clinically asymptomatic individuals harbouring pathogenic mitochondrial DNA (mtDNA) mutations in the cardiac muscle may have sudden cardiac death (SCD) as the first manifestation of mitochondrial disease. We investigated the contribution of pathogenic mtDNA point mutations and mtDNA haplogroups in cardiac muscle in a cohort of 280 Finnish subjects that had died from non-ischaemic SCD with the median age of death at 59 years and in 537 population controls. We did not find any common or novel pathogenic mutations, but the frequency of haplogroup H1 was higher in the SCD subjects than that in 537 population controls (odds ratio: 1.76, confidence interval 95%: 1.02-3.04). We conclude that, at the population level, pathogenic point mutations in mtDNA do not contribute to non-ischaemic SCD, but natural variation may modify the risk.