ONLINE MEDICAL GENETICS IN PRACTICE Bayesian risk assessment for autosomal recessive diseases: fetal echogenic bowel with one or no detectable CFTR

Prenatal riskassessment for autosomal recessive diseases can be particu-larly complex when, for example, only one mutation isdetectable in the fetus, and when mutation detection ratesand disease allele frequencies vary among different ethnicgroups. A classic example is the risk assessment for a fetuswith echogenic bowel and only one detectable mutation inthe cystic fibrosis transmembrane conductance regulator(CFTR) gene. The fetus could be affected or be a carrier on thebasis of the presence of one detectable mutation. Accuraterisk assessment in this scenario may be critical for parentaldecision making.Cystic fibrosis is the most common severe autosomalrecessive disorder; it affects about one in 2500 live births andhas a carrier frequency of about one in 25 among EuropeanCaucasians.