If an infant’s diapers have a reddish discoloration, what genodermatosis should you include in your differential diagnosis?

Erythropoietic porphyria. This is another very rare autosomal recessive disorder due to an absence in uroporphyrinogen III cosynthase, an enzyme required early in the heme synthesis pathway. Much of the excess substrate is excreted in the urine and may give diapers a distinctive reddish color. Patients develop a destructive, scarring photodermatitis and a variety of hematologic abnormalities. In acute intermittent porphyria, the urine of adolescents and adults may turn red upon standing also.