Profound hypotonia in an infant with δ-aminolevulinic acid dehydratase deficient porphyria

δ-Aminolevulinic acid (ALA) dehydratase (ALAD) deficient porphyria (ADP) is an extremely rare form of porphyria, with only eight documented cases. Herein, we report the second known case of ADP in the Western hemisphere and third case with infantile onset of symptoms. A male neonate presented on day three of life with profound hypotonia, pinpoint pupils, absent deep tendon reflexes, and anemia. Whole genome sequencing revealed two pathogenic missense ALAD variants, and subsequent biochemical testing confirmed a diagnosis of ADP. With supportive care and following erythrocyte transfusions for anemia, his hypotonia improved gradually. Neurological improvement following erythrocyte transfusion may have resulted from suppression of erythropoiesis and less overproduction of ALA and porphyrins by the marrow, which is an important consideration for long term management. This case highlights the importance of leveraging rapid whole genome sequencing for the diagnosis and minimization of devastating sequelae of exceptionally rare disorders, such as ADP.