Two unusual cases of first trimester prenatal diagnosis of cystic fibrosis using DNA probes

There are now several DNA probes which localize the cystic fibrosis mutation (CF) to chromosome 7q2.2-q3.1. The most tightly linked probes, pJ3.11 and met, are useful for first trimester prenatal diagnosis for many families provided that there is at least one living child affected by CF (Farrall et al., 1986). We describe here two families seeking prenatal diagnosis for CF which present unusual counselling problems. The first is an extended family in which there is no living affected member with CF; the second, a consanguinous marriage at risk both for cystic fibrosis and β-thalassaemia. In both cases first trimester chorionic villus sampling and DNA haplotype analysis predicted that the fetus is a carrier for CF, and in the doubly affected family a carrier for β-thalassaemia as well. Both pregnancies resulted in live births and subsequent immunoreactive trypsin estimations were both in the normal range.