MUTATION ANALYSIS FOR HETEROZYGOTE DETECTION AND THE PRENATAL-DIAGNOSIS OF CYSTIC-FIBROSIS

The cystic fibrosis gene was recently cloned, and a three-base deletion removing phenylalanine 508 from the coding region was identified as the mutation on the majority of cystic fibrosis chromosomes. We used the polymerase chain reaction and hybridization with allele-specific oligonucleotides to analyze the presence or absence of this mutation on 439 cystic fibrosis chromosomes and 433 normal chromosomes from non-Ashkenazic white families. This mutation was present on 75.8 percent of the cystic fibrosis chromosomes. Using the DNA markers XV-2c and KM-19, we found that 96 percent of cystic fibrosis chromosomes with the mutation had a single DNA haplotype that occurs frequently with cystic fibrosis chromosomes. This haplotype was also found on 54 percent of the cystic fibrosis chromosomes without the three-base deletion. The three-base deletion was found on only 30.3 percent of cystic fibrosis chromosomes from Ashkenazic families, although the common cystic fibrosis haplotype was present on 97 percent of cystic fibrosis chromosomes from Ashkenazic families. The ability to detect the common mutation causing cystic fibrosis represents a major improvement in prenatal diagnosis and heterozygote detection, particularly in families in which no DNA sample is available from the affected child, and provides an improved method of testing for spouses of carriers of cystic fibrosis. Mutation analysis introduces the possibility of population-based screening programs for carriers, which on the basis of the sample in this study, would currently identify about 57 percent of the non-Ashkenazic white couples at risk. CYSTIC fibrosis is the most common severe autosomal recessive genetic disorder affecting the white population. A review of the clinical, physiologic, and genetic aspects of cystic fibrosis has been published recently.1 The reported disease frequency in white populations varies markedly, but the incidence in North American whites is probably close to 1 in 2500.1 This implies a gene frequency of 1 in 50 and a carrier frequency of about 1 in 25.5. The cystic fibrosis locus was linked to a DNA polymorphism in 1985,2 and the gene was localized to the long arm of human chromosome 7.3 4 5 Subsequently, segments of… © 1990, Massachusetts Medical Society. All rights reserved.