Protease inhibitor (PI) phenotype of individuals with chromosomal fragile sites.

One hundred and four fragile sites were ascertained from 95 unrelated families. In each family the ancestry of the fragile site was traced as far as possible and the PI phenotype of the carrier in the earliest generation determined. Mildly deficient PI phenotypes were more prevalent than expected among earliest carriers of folate sensitive fragile sites, but not for BrdU dependent fragile sites. The significance of this finding is unclear and is based upon relatively small numbers. Another series of fragile site carriers would need to be studied and similar results found before the question of any relationship between PI phenotype and mutagenesis to fragile sites could be raised.