Genetic testing worthwhile in sudden cardiac death

By Eleanor McDermid

Genetic testing and family screening help to provide explanations for sudden cardiac death in children and young adults, shows a population-based study.

The research, which appears in The New England Journal of Medicine, covers all 490 sudden cardiac deaths in people aged 1-35 years in Australia and New Zealand over a 2-year period.

The overall rate was 1.3 cases per 100,000 persons of that age, with 72% of cases being boys or young men. The incidence was lowest between the ages of 6 and 15 years, and rose with age thereafter.

"A clinically important finding was that the majority of sudden cardiac deaths occurred either while the person was sleeping or at rest", say Christopher Semsarian (University of Sydney, New South Wales, Australia) and colleagues.

Thirty percent of explained cardiac deaths and 48% of unexplained cases occurred while the person was actually asleep, and nearly as many occurred when people were at rest, with only 17% and 13%, respectively, occurring when the person was exercising.

The researchers say this "raises questions about the efficacy of limiting physical activity" in people considered to be at risk of sudden cardiac death. They advise that "strategies to prevent sudden cardiac death among children and young adults should also focus on gaining a better understanding of the mechanisms associated with death that occurs while a person is sleeping or at rest."

The cause of cardiac death was initially unexplained in 198 (40%) patients and was the most common categorisation in all age groups except 31 to 35 year-olds, in whom coronary artery disease was the most common explanation, accounting for 79 of the 173 deaths in this age group.

Inherited cardiomyopathies accounted for 16% of cases and aortic dissection accounted for 4% of cases, all among young adults, while myocarditis accounted for 7% of cases and was the second-most common categorisation in children aged 1-5 years, after unexplained (76%).

The team obtained permission for genetic analysis of 113 unexplained cases, and found that mutations in the four conventional molecular autopsy genes (for long QT syndrome and ventricular tachycardia) explained 9% of these deaths. Further analysis of genes with a role in cardiac arrhythmia; major, minor and rare cardiomyopathy; and epilepsy increased the proportion of cases with at least a probable explanation to 27%.

"Establishing a clear genetic diagnosis in cases of unexplained sudden cardiac death has major implications for the identification of at-risk relatives, the initiation of strategies to prevent sudden death, and guidance with respect to reproductive options", the researchers comment.

Clinical screening of the case's family was possible in 98 instances, leading to a diagnosis in 13%.

The team concedes this is a fairly low diagnostic yield, reflecting the population-based study design, but says: "A thorough clinical evaluation of surviving at-risk family members is nonetheless strongly recommended and may be supplemented by a molecular autopsy."

Source: N Engl J Med 2016; 374: 2441-2452

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