Estimation of risk for families with Robertsonian translocations

Segregation analysis was applied to family data in which a Robertsonian translocation was present. The risk for balanced translocation carriers, trisomy due to translocation, spontaneous abortion and interchromosomal effects was estimated when accounting for mode of ascertainment from various sources of families. Specifically, risk estimates for a 13/14 translocation were obtained using 37 sibships from several published studies, in which ascertainment was identified and chromosomal testing of individuals was noted. Sporadic cases were excluded. After adjustment for ascertainment bias, the segregation ratios were as follows: for a balanced heterozygote, p = 0.60 ± 0.04; for trisomy 13, p = 0.014 ±0.007; for spontaneous abortion, p = 0.20 ± 0.024; and for interchromosomal effects, p = 0.017 ± 0.008. No heterogeneity between sexes or ascertainments was detected. In agreement with previous studies on D/D' translocations, the probability of a 13/14 balanced heterozygote was found to be slightly higher than the expected value of 0.50; however, the risk of trisomy 13 in segregating families was low. The risk for spontaneous abortion did not exceed the incidence in the general population.