First-trimester prenatal diagnosis of cystic fibrosis with linked DNA probes.

Linkage analysis with cloned gene probes has shown that the mutation causing cystic fibrosis is located in the middle of the long arm of chromosome 7. First-trimester diagnosis of cystic fibrosis is reported in four informative families and second-trimester diagnosis in one family with fetal DNA prepared from chorionic villi, hybridised with the tightly linked DNA probes, pJ3.11 and met. Risk calculations show that the expected false-negative and false-positive rates are approximately 2% and 6%, respectively, for typical nuclear families with one affected living child. Existing probes are sufficiently informative to allow full diagnosis in about two-thirds of couples presenting with at least one affected child. In half of the remainder, the inheritance of one parental mutant chromosome can be deduced.