Haplotipe–analise van die fenielalanienhidroksilase–lokus in families met fenielketonurie
Cloning of a full-length human cDNA for phenylalanine hydroxylase (PAH) has led to major advances In the application of recombinant DNA techniques to the study of classical phenylketonuria (PKU) I a common autosomal recessive inborn error of amino acid metabolism (Ledley et al, 1985b). In order to assess the possible application of RFLP analysis for the identification of carriers of the trait among South African Caucasians, the frequencies of eight restriction site polymorphisms in a panel of random Caucasians were determined using a human PAH cDNA clone (obtained from S. L. C. Woo). The frequencies of the minor alleles exceed 0,12 for all of the restriction endonukleases, confirming the existence of a very high degree of polymorphism at the human PAH locus. Moreover, in the panel of random Caucasian individuals, 35 out of 36 are RFLP heterozygotes, which yielded an observed heterozygosity of 97%. The data, therefore, suggest that a large percentage of South African Caucasian PKU families may be successfully analysed with RFLP haplotype analysis. In all of the families thus far studied digestion by a battery of eight selected restriction endonucleases yielded RFLP patterns which were informative for either the detection of homozygotes for the defective PAH alleles or the identification of carriers of the PKU trait. Of particular interest is the finding that none of the observed eight haplotypes associated with defective PAH alleles show a predominant distribution. This may indicate that the various PKU alleles do not have a common origin, or that the PAH gene is especially prone to recombination events. In fact, we have observed a meiotic crossing-over event between two PAH alleles in a large family. Various facets of my work have been presented at international and local scientific meetings.