Allelic heterogeneity in Group A xeroderma pigmentosum

The molecular basis of Group A xeroderma pigmentosum was investigated by restriction fragment length polymorphism analysis of PCR-amplified DNA sequences using the two restriction enzymes, endonucleases AlwN I and Hph I. The clones of a patient with Group A xeroderma pigmentosum who had typical symptoms showed a G-C substitution at the 3' splice acceptor site of intron 3. However, of the two atypical Group A xeroderma pigmentosum patients with mild skin lesions and minimal neurological abnormalities, the milder one showed homozygosity for the nonsense mutation of exon 6, while the other patient with slightly greater central nervous involvement was shown to be a compound heterozygote for the splicing mutation of intron 3 and the nonsense mutation of exon 6, thus indicating an allelic heterogeneity in group A xeroderma pigmentosum.