Late onset of skin cancers in 2 xeroderma pigmentosum group F siblings and a review of 30 Japanese xeroderma pigmentosum patients in groups D, E and F.

Sib patients with xeroderma pigmentosum (XP), XP90TO (42 years old, male) and XP92TO (40 years old, female, were assigned to group F by the complementation analysis in hybridized heterodikaryons. The XP90TO and XP92TO fibroblasts exhibited the typical XPF characteristics of a threefold higher sensitivity to the lethal effect of 254 nm UV and a reduced level of 12% unscheduled DNA synthesis (UDS) compared with normal cells. Clinically, both patients manifested moderate to severe acute sun sensitivity by age 8, pigmented freckles by age 10 and skin malignancies at higher ages (6 basaliomas at 42 years in XP90TO; 1 basalioma at 41 years in XP92TO). Despite the still currently sun-sensitive state, the patients showed normal minimal erythema dose (MED) at monochromatic wavelengths of 290, 300 and 305 nm but abnormally delayed peaking of erythema reaction at 48 h after exposure. After irradiation with more than 3 MED, XP92TO showed a long persistence of induced erythema for at least 7 days. A review of the 16 reported XPF patients indicated mild skin manifestations, no neurological abnormalities, and more delayed skin carcinogenesis at a lower frequency than that in XPA patients. In addition, we have collected clinical information from Japanese XP patients in rare complementation groups D and E and reviewed their clinical and photobiological characteristics.