AR indicates autosomal recessive; AD, autosomal dominant; XL, X-linked; NV, neurovisceral; CP, cutaneous photosensitivity; and —, not applicable.

*Increases that may be important for diagnosis.

†A polymorphism in intron 3 of the wild-type allele affects the level of enzyme activity and clinical expression.

‡Increased activity resulting from “gain-of-function” mutations in ALAS2 exon 11.