 Patients in the XPE group have mild dermatological manifestations and are neurologically unaffected.Mutation in the "DDB2" gene causes a deficiency in nucleotide excision repair of DNA.This deficiency is also mild, showing 40 to 60% of normal repair capability and a modest sensitivity to UV light in comparison to the sensitivities of cells defective in the other XP genes XPA, XPB, XPC, XPD, XPF and XPG.