The Swedish long QT syndrome R518X/KCNQ1 founder population- origin and clinical phenotype : phenotypic variability partly explained by gender-specific effects of sequence variants in the NOS1AP gene

• Background: Genetic modifiers have been proposed to explain phenotypic variability in the long QT syndrome (LQTS). We investigate the origin and phenotype of the worldwide common R518X/KCNQ1 mutation in Sweden, as well as possible associations between p.R518X-LQTS phenotype and previously reported modifying sequence variants in the NOS1AP, KCNH2, KCNE1, SCN5A and KCNQ1(3’UTR) genes. Methods and Results: We identified 19 p.R518X families (101 mutation-carriers, whereof 15 Jervell and Lange-Nielsen (JLNS) cases and 86 LQTS cases). Analyses of microsatellite markers, genealogy and mutation age (ESTIAGE) identified a common northern origin ~700 years ago for 17/19 families and a high prevalence of Swedish p.R518X heterozygotes was suggested (DMLE). Clinical phenotype ranged from severe in JLNS to relatively benign in LQTS (QTc 576±61 ms vs. 462±34 ms, cumulative incidence of (aborted) cardiac arrest 47% vs 1%, annual non-medicated incidence rate (aborted) cardiac arrest 4% vs. 0.04%).In p.R518X-LQTS males, two NOS1AP variants rs12143842 and rs16847548 were associated with a 29 ms QT prolongation (p=0.004), explaining 27% of QTc variability.Three derived 3’UTR-KCNQ1 variants, previously shown to suppress gene expression in an allele-specific manner, were found to segregate with the founder mutation.Conclusion: The R518X/KCNQ1 mutation is a Swedish founder mutation presenting with an expectedly severe phenotype in JLNS and an unusually mild phenotype in LQTS, although intra-familial variability remained. Gender-specific effects of NOS1AP sequence variants explained over a fourth of QTc variance in p.R518X-LQTS males, warranting further studies. Repressive 3’UTR-KCNQ1 sequence variants segregating within the founder haplotype could possibly contribute to its relative benignancy.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Pediatrik (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Pediatrics (hsv//eng)

Nyckelord

Long QT Syndrome

Jervell and Lange-Nielsen Syndrome

founder effects

genealogy

genetics

origin

haplotype analysis

mutation age

clinical phenotype

KCNQ1 gene

modifier genes

sequence variants

risk stratification

pediatrik

Pediatrics

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vet (ämneskategori)

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