ALAS2 and Cutaneous photosensitivity: Accumulation of PP-IX in this disorder results in severe skin photosensitivity [11], ALAS2 (step 1) gain-of-function mutations result in X-linked porphyria, which, similar to erythropoietic porphyria, is also associated with cutaneous PP-IX accumulation and skin photosensitivity [11,61].