COUNSELING RISK FIGURES FOR FRAGILE-X CARRIER FEMALES OF VARYING BANDSIZES FOR USE IN PREDICTING THE LIKELIHOOD OF RETARDATION IN THEIR OFFSPRING

We have derived risk figures for fra(X) syndrome carrier mothers based on their DNA status. Clinical and molecular information was analysed in 200 carrier mothers and their offspring. Individuals were classifie d as affected by a requirement for special education. Risk figures wer e calculated using the genotype of the intellectually normal offspring in order to reduce ascertainment bias. Analysis was made on women wit h differing mutation size to predict the proportion of affected offspr ing. Using this method the following risk figures were derived: 1. For carrier women with an increase (Delta) of 0.06-0.14 Kb, the risk for having an affected son was 29% (1 in 3.5) and 25% for daughters (1 in 4). This predicts an overall 73% chance of a normal child. 2. For Delt a size 0.15-0.24 Kb, the risk of having an affected son was 46% (1 in 2.2) and 32% for daughters (1 in 3.1), predicting a 61% chance of a no rmal child. 3. For Delta size >0.24 Kb, normal transmitting male offsp ring were not seen, i.e., the risk for males was 50% (1 in 2) and for females 32% (1 in 3.1) which predicts a 59% chance of a normal child. (C) 1994 Wiley-Liss,Inc.