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.