Assignment of three Chinese xeroderma pigmentosum patients to complementation group C and one to group E

Heterozygous individuals bearing a founder mutation in the XPA DNA repair gene comprise nearly 1% of the Japanese population

Individuals who are homozygotes for mutations in DNA repair genes are at high risk for cancer. It is not well documented, however, if the heterozygous carriers of the mutation are also predisposed to cancer. To address the issue, xeroderma pigmentosum (XP) in Japan is an interesting candidate because of three major reasons: XP is an autosomal recessive disorder with an enormously elevated risk of skin cancer, the frequency of XP patients is higher in Japan than in other parts of the world, and more than half of Japanese XP patients are homozygous for the same founder mutation in the XPA gene. We screened archival blood samples from Japanese individuals who resided in Hiroshima or Nagasaki. A simple PCR-RFLP method was developed that is highly specific for detection of XPA heterozygotes carrying the founder mutation. We identified nine XPA heterozygotes among 1,020 individuals screened for a prevalence of 0.88%. This rate, if representative, implies that there are about 1 million carriers of the XPA founder mutation in the Japanese population. Thus, investigation of their cancer risk may be warranted.

Useful applications of DNA repair tests for differential diagnosis of atypical dyschromatosis symmetrica hereditaria from xeroderma pigmentosum

Dyschromatosis symmetrica hereditaria (DSH) is a hereditary skin disease characterized by the presence of pigmented and hypopigmented macules on the extremities and freckles on the face. However, if clinical features are not fully developed in infantile patients, it is difficult to differentiate DSH from xeroderma pigmentosum by clinical features alone. A 2-year-old boy (patient 1), revealed atypical features of DSH with slight susceptibility to sunburn. However, his grandfather (patient 4) who was 67 years old, revealed typical features of DSH, which helped to make an exact diagnosis in patient 1. For patient 2, a 5-year-old boy, and patient 3, a 3-year-old girl, it was more difficult to make a diagnosis because there were no family members with DSH features. DNA repair ability was tested for all four cases by means of unscheduled DNA synthesis and colony formation of skin fibroblasts after ultraviolet light irradiation, which resulted in an accurate diagnosis of DSH. We propose that these tests be performed to make a diagnosis of DSH in the case of poor or atypical clinical symptoms.