A GENETIC-BASIS FOR THE SUDDEN-INFANT-DEATH-SYNDROME SEX-RATIO

Sudden infant death syndrome, in 36 global data sets comprising 67 378 postneonatal autopsied cases, has a male fraction of 0.612 which is s ignificantly greater than the male birth fraction of 0.5122. Each of t he sex ratios in the 36 data sets cannot be rejected as a random sampl e from a P=0.612 binomial distribution. We hypothesize that an X-linke d two-allele (a,A) single gene may be responsible for this consistent behavior. The Hardy-Weinberg principle predicts, given a 5% excess mal e birth rate, that a recessive allele (a) associated with sudden infan t death syndrome, having a frequency of q = 2/3, could be responsible for the male fraction of 0.612. The absence of the A allele would be a necessary precondition for sudden infant death syndrome. We hypothesi ze that the syndrome occurs only with additional rare environmental co nditions and rare physiological factors leading to extreme hypoxic str ess, which reduces the sudden infant death syndrome rate to the order of 1 per 1000 live births.