5-Aminolevulinate dehydratase porphyria: Update on hepatic 5-aminolevulinic acid synthase induction and long-term response to hemin

Abstract

Background: 5-Aminolevulinic acid dehydratase (ALAD) porphyria (ADP) is an ultrarare autosomal recessive disease, with only eight documented cases, all of whom were males. Although classified as an acute hepatic porphyria (AHP), induction of the rate limiting hepatic enzyme 5-aminolevulinic acid synthase-1 (ALAS1) has not been demonstrated, and the marrow may also contribute excess 5-aminolevulinic acid (ALA). Two patients have died and reported follow up for the others is limited, so the natural history of this disease is poorly understood and treatment experience limited.

Methods: We report new molecular findings and update the clinical course and treatment of the sixth reported ADP patient, now 31 years old and the only known case in the Americas, and review published data regarding genotype-phenotype correlation and treatment.

Results: Circulating hepatic 5-aminolevulinic acid synthase-1 (ALAS1) mRNA was elevated in this case, as in other AHPs. Gain of function mutation of erythroid specific ALAS2 - an X-linked modifying gene in some other porphyrias - was not found. Seven reported ADP cases had compound heterozygous ALAD mutations resulting in very low residual ALAD activity and symptoms early in life or adolescence. One adult with a germline ALAD mutant allele developed ADP in association with a clonal myeloproliferative disorder, polycythemia vera.

Conclusions: Elevation in circulating hepatic ALAS1 and response to treatment with hemin indicate that the liver is an important source of excess ALA in ADP, although the marrow may also contribute. Intravenous hemin was effective in most reported cases for treatment and prevention of acute attacks of neurological symptoms.

Keywords: 5-aminolevulinic acid dehydratase; 5-aminolevulinic acid dehydratase deficiency porphyria; 5-aminolevulinic acid synthase; Acute porphyria; Human hemin; Porphyrins.