Synonyms for ALAD: porphobilinogen synthase, ALA dehydrase
Inheritance: autosomal recessive
Genetic locus: 9q34
Clinical features in a homozygous patient:
(1) very low serum concentrations of ALAD
(2) clinical picture resembling acute intermittent porphyria (neurovisceral signs and symptoms without skin lesions)
Clinical features in a heterozygous patient:
(1) reduced but usually adequate serum concentrations of ALAD
(2) exposure to low levels of lead can trigger porphyria
Acquired ALAD deficiency can occur in lead poisoning. Other enzymes that are inhibited by lead include coproporphyrinogen oxidase and ferrochetolase. These patients will not carry a mutation in ALAD but will have elevated lead levels.
Laboratory findings:
(1) elevated urine coproporphyrin III
(2) ALA will be in the urine with reduced to absent porphobilinogen
(3) zinc protoporphyrin within erythrocytes
(4) no elevation of porphyrins in the feces
