FECH and X-linked lymphoproliferative disease: Erythropoietic protoporphyria (EPP) and X-linked protoporphyria (XLP) are rare genetic photodermatoses with an estimated prevalence between 1.0 to 2.7 in 200,000 among the Caucasian population; however, the frequency of pathogenic ferrochelatase (FECH) mutations in the UK Biobank database suggests the potential for a higher prevalence of approximately 11.8 in 200,000 [13,14,15].