Assignment of 2 patients with xeroderma pigmentosum to complementation group E

Xeroderma pigmentosum (XP) fibroblast strains derived from XP24KO and XP26KO patients with mild clinical manifestations were similarly twice as sensitive to 254 nm UV killing as normal cells and had a reduced level of 30-55% unscheduled DNA synthesis (UDS) after irradiation with 10 J/m2. Complementation analysis in the hybridized heterodikaryons revealed that XP24KO and XP26KO cells were only unable to complement the reference XP2RO group E cells, despite sufficient complementation to give rise to the normal level of UV-induced UDS with cells of all the other reference XP groups. Nor did XP24KO cells complement XP26KO cells. Therefore, the above 2 unrelated XP patients were assigned to complementation group E. The present group E assignment is the first in Japan, and perhaps the second in the world, the first being the XP2RO/XP3RO second-cousin relationship in The Netherlands (now 4 patients in group E).