While, as mentioned, all these acute porphyrias are inherited as an autosomal dominant disease, ADP is inherited in an autosomal recessive way, therefore being an extremely rare porphyria with only six certain reported cases confirmed by DNA studies.36 This type of porphyria results from a deficiency of the aminolevulinic acid dehydratase (ALAD) enzyme, resulting in a unique biochemical pattern during an acute attack with elevated urinary ALA level and a normal urinary PBG level (Figure 1). Here, ALAD is linked to porphyria.