Unusual behaviour of a human autosome having two rare folate sensitive fragile sites.

A mother and daughter who have two rare folate sensitive fragile sites on the same homolog of chromosome 12 are recorded. This confirms the folate sensitive nature of the fragile site at 12q24.13. The behaviour of the chromosome with the two fragile sites is described, which includes the propensity for the two fragile sites to associate with each other when simultaneously expressed.