Non-random Chromosome Losses in Down's Syndrome

Abstract

THE opinion has been expressed that chromosome losses in cultured human leucocytes are related to sex, age and chromosome size^1–4. Working with normal (euploid) individuals, Bloom et al.³ and Neurath et al.⁴ reported an apparent linear relationship between chromosome size and the probability of loss for chromosomes of groups A to F. Specifically, the very small G chromosomes were missing even more often than could be predicted for the regression on chromosome size in groups A to F. Studying losses of single chromosomes in cases of Down's syndrome (mongolism), Mikkelsen found a significant deficit of cells lacking a large chromosome (group A or B). Greater than expected losses in group G/Y were detected in the parents, but not in the mongoloid children. F chromosomes were also missing more frequently than expected in male mongoloids and their fathers, but not in female mongoloids or their mothers. These studies all involved cells with only a single missing chromosome.