Abstract: The invention generally concerns methods and compositions for screening individuals for predicting increased sudden death risk in a population of subjects having long QT syndrome (LQTS) or subjects at risk for sudden infant death syndrome (SIDS) by examining single nucleotide polymorphisms (SNPs) in the NOS1AP gene. In particular, the minor alleles for both rs16847548 and rs4657139 predicted an increased risk for sudden death in LQTS, while subjects carrying the GG or TG genotype (G is the minor allele) for rs10494366 were at increased risk of sudden death from SIDS. This information permits more attentive monitoring and/or prophylactic treatments of high risk individuals.