Mortality and causes of death in females with extra X chromosomes and males with extra Y chromosomes.

A prospective study of mortality in females with extra X chromosomes and males with extra Y chromosomes is reported. Among the 94 females who survived infancy and were then observed on average for 16 years there were 24 deaths compared with an expected mortality of 10.7. The greater than twofold increase is highly significant (p less than 0.005). The deaths were due to a variety of diseases but no significant increase from any single cause could be identified. Among 136 males with extra Y chromosomes observed on average for 12 years there were 10 deaths. This number is not significantly greater than the expected 6.4. No increase in mortality from a single cause was observed.