Segregation analysis of rare autosomal folate sensitive fragile sites.

We have studied 12 families with rare autosomal folate sensitive fragile sites (RAFSFS). Of these, 9 were informative for segregation analysis of fragile sites in order to assess differences in parental transmission. We identified 20 families with RAFSFS from the literature from 1985 to 1989; thirteen of these were informative for segregation analysis. Segregation analysis confirmed that paternal fragile site transmission rates deviated significantly from the expected 50% for a Mendelian co-dominant trait. Sex ratio comparisons showed a significant excess of transmitting females and a significant excess of males among fragile site non-carriers from the literature families. Comparison of the fragile site carriers with non-carriers in the combined data showed a non-significant excess of non-carriers. We confirmed a deficiency of offspring expressing fragile sites when transmission was through fathers, suggesting gametic selection or the phenomenon of parental genomic imprinting.