Cardiac channel molecular autopsy: insights from 173 consecutive cases of autopsy-negative sudden unexplained death referred for postmortem genetic testing

Abstract

Objective: To perform long QT syndrome and catecholaminergic polymorphic ventricular tachycardia cardiac channel postmortem genetic testing (molecular autopsy) for a large cohort of cases of autopsy-negative sudden unexplained death (SUD).

Methods: From September 1, 1998, through October 31, 2010, 173 cases of SUD (106 males; mean ± SD age, 18.4 ± 12.9 years; age range, 1-69 years; 89% white) were referred by medical examiners or coroners for a cardiac channel molecular autopsy. Using polymerase chain reaction, denaturing high-performance liquid chromatography, and DNA sequencing, a comprehensive mutational analysis of the long QT syndrome susceptibility genes (KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2) and a targeted analysis of the catecholaminergic polymorphic ventricular tachycardia type 1-associated gene (RYR2) were conducted.

Results: Overall, 45 putative pathogenic mutations absent in 400 to 700 controls were identified in 45 autopsy-negative SUD cases (26.0%). Females had a higher yield (26/67 [38.8%]) than males (19/106 [17.9%]; P<.005). Among SUD cases with exercise-induced death, the yield trended higher among the 1- to 10-year-olds (8/12 [66.7%]) compared with the 11- to 20-year-olds (4/27 [14.8%]; P=.002). In contrast, for those who died during a period of sleep, the 11- to 20-year-olds had a higher yield (9/25 [36.0%]) than the 1- to 10-year-olds (1/24 [4.2%]; P=.01).

Conclusion: Cardiac channel molecular autopsy should be considered in the evaluation of autopsy-negative SUD. Several interesting genotype-phenotype observations may provide insight into the expected yields of postmortem genetic testing for SUD and assist in selecting cases with the greatest potential for mutation discovery and directing genetic testing efforts.

FIGURE 1

Summary of cardiac channel mutations in long QT syndrome (LQTS)–associated genes identified in a series of autopsy-negative sudden unexplained death (SUD). The putative, pathogenic SUD-associated mutations (gray circles) and additional nonsynonymous, functional polymorphisms (white circles) identified in this study are depicted with their proximate location on the linear topologies (not drawn to scale) of the LQT1-associated KCNQ1-encoded cardiac Kv7.1/I_Ks potassium channel α-subunit (A), the LQT2-associated KCNH2 encoded cardiac Kv11.1/I_Kr potassium channel α-subunit (B), the LQT3-associated SCN5A encoded cardiac Nav1.5/I_Na sodium channel α-subunit (C), the LQT5-associated KCNE1-encoded cardiac Kv7.1 potassium channel β-subunit (D), and the LQT6-assoicated KCNE2-encoded cardiac Kv11.1 potassium channel β-subunit (E). Asterisk indicates novel mutation absent in the published literature. The numbers within parentheses represent the number of times the variant was seen in cases. For example, R1047L (×3) is a functional polymorphism seen in 3 cases.

FIGURE 2

Summary of cardiac channel mutations in the catecholaminergic polymorphic ventricular tachycardia type 1 (CPVT1)–associated RYR2-encoded calcium release channel (cardiac ryanodine receptor) identified in a series of autopsy-negative sudden unexplained death (SUD). The putative, pathogenic SUD-associated mutations (gray circles) and nonsynonymous polymorphisms (white circles) identified in this study are depicted with their proximate location on the linear topologies (not drawn to scale) of the CPVT1-associated RYR2-encoded calcium release channel (cardiac ryanodine receptor) α-subunit. Asterisk indicates novel mutation. The numbers within parentheses represent the number of times the variant was seen in cases.

FIGURE 3

The percent distribution of mutations identified in the catecholaminergic polymorphic ventricular tachycardia (CPVT)–associated RYR2 gene compared with mutations identified in the long QT syndrome (LQTS)–associated genes for the 19 mutation-positive males and the 26 mutation-positive females. The numbers in the bars represent the numbers of cases with a mutation. For example, 11 of 19 (57.9%) mutation-positive males had a CPVT-associated RYR2 mutation compared with 8 males (42.1%) who had a mutation in an LQTS-associated gene (KCNQ1, KCNH2, SCN5A, KCNE1, or KCNE2).

FIGURE 4

Genotype distribution in sudden unexplained death cases among the mutation-positive overall cohort (n=45), mutation-positive males (n=19), and mutation-positive females (n=26). Again, individuals with a functional polymorphism that might have contributed to the sudden unexplained death were excluded from this calculation. Instead, only the 45 decedents with a rare, potentially channelopathic mutation were counted.

FIGURE 5

The yield of mutation detection for different age groups in 10-year intervals (1-10, 11-20, 21-30, 31-40, 41-50, and >50 years) for both males (M) and females (F). The numbers in parentheses represent the total number of cases, and the numbers below the F or M represent the numbers of females or males in the respective category. The numbers in the bars represent the absolute number of cases with a mutation, with the percent yield of mutation detection highlighted above the bars.

FIGURE 6

The different yield of mutation detection among the 3 main categories of sudden unexplained death–associated triggers or events (exertion, nonspecific, and sleep) for the overall cohort, females, and males at all ages. The numbers below the bars represent the number of cases in each category. The numbers within the bars represent the actual number of cases with a mutation, with the percent yield of mutation detection highlighted above the bars.

FIGURE 7

The difference in mutation detection between children aged 1 to 10 years and adolescents aged 11 to 20 years with either exertion- or sleep-associated sudden death. The numbers below O, F, and M represent the number of cases in each category. The numbers within the bars represent the absolute number of cases with a mutation, with the percent yield of mutation detection highlighted above the bars. F = females; M = males; O = overall.

FIGURE 8

The differences observed in genotype distribution among mutation-positive female (n=7) and males (n=6) with sleep-associated sudden unexplained death (SUD) and female (n=8) and male (n=8) with exertional SUD.

FIGURE 9

The difference in mutation detection yield between patients with sudden unexplained death (SUD) with either a negative (n=89) or positive (n=70) personal or family history of cardiac events or other “warning” signs, including seizures (n=12), syncope (n=25), or sudden cardiac death (n=20). The numbers in the bars represent the numbers of cases with a mutation, with the percent yield of mutation detection highlighted above the bars.