Survival of two patients with severe delta-aminolaevulinic acid dehydratase deficiency porphyria

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

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.

Effects of extracellular δ-aminolaevulinic acid on sodium currents in acutely isolated rat hippocampal CA1 neurons

The effects of delta-aminolaevulinic acid (ALA) on voltage-gated sodium channel (VGSC) currents (I(Na)) in acutely isolated hippocampal CA1 neurons from 10- to 12-day-old Wistar rats were examined by using the whole-cell patch-clamp technique under voltage-clamp conditions. ALA from 0.01 microm to 20 microm was applied to the recorded neurons. Low concentrations of ALA (0.01-1.0 microM) increased I(Na) amplitude, whereas high concentrations of ALA (5.0-20.0 microM) decreased it. The average I(Na) amplitude reached a maximum of 117.4 +/- 3.9% (n = 9, P < 0.05) with 0.1 microM ALA, and decreased to 78.1 +/- 3.8% (n = 13, P < 0.05) with 10 microm ALA. ALA shifted the steady-state activation and inactivation curves of I(Na) in the hyperpolarizing direction with different V0.5, suggesting that ALA could depress the opening threshold of the voltage-gated sodium channel (VGSC) and thus increase the excitability of neurons through facilitating the opening of VGSC. The time course of recovery from inactivation was significantly prolonged at both low and high concentrations of ALA, whereas either low or high concentrations of ALA had no significant effect on the attenuation of I(Na) during stimulation at 5 Hz, indicating that the effect of ALA on VGSC is state-independent. Furthermore, we found that application of ascorbic acid, which blocks pro-oxidative effects in neurons, could prevent the increase of I(Na) amplitude at low concentrations of ALA. Baclofen, an agonist of GABAb receptors, induced some similar effects to ALA on VGSC, whereas bicuculline, an antagonist of GABAa receptors, could not prevent ALA-induced effects on VGSC. These results suggested that ALA regulated VGSC mainly through its pro-oxidative effects and GABAb receptor-mediated effects.

The third case of Doss porphyria (delta-amino-levulinic acid dehydratase deficiency) in Germany

Delta-aminolevulinic acid dehydratase (ALAD) deficiency porphyria, or Doss porphyria, was first reported in Germany in 1979. Only four bona fide cases of Doss porphyria have been reported to date that were confirmed by immunological and molecular analyses of their ALAD mutations. Here we describe the fifth case of Doss porphyria. A 17-year-old German male suffered from colicky abdominal pain and severe polyneuropathy for 2 years. Urinary delta-aminolevulinic acid (ALA) was increased 32-fold, and coproporphyrin 76-fold compared with the upper limit of their respective normal ranges. Urinary excretion of porphobilinogen (PBG) and uroporphyrin was only slightly increased. Faecal porphyrins were within the normal range. Erythrocyte zinc protoporphyrin concentrations were elevated 5.4-fold. ALAD activity in erythrocytes was decreased to 10% of the normal value, and was not activated by zinc and by dithiothreitol. Blood lead levels were within the normal range, excluding lead poisoning in the proband. Erythrocyte ALAD activity was about one-half of the normal value in both parents, whereas it was normal in the proband's brother. Urinary excretion of ALA, PBG and total porphyrins was within the normal range in both parents and the brother. Molecular genetic studies of the ALAD gene in the proband revealed two base changes, C to A and C to T, both in intron 3 at -11 bp upstream of the exon 3 start site. In addition to the proband, the father carried the (-11)C-to-T, while the mother carried the ALAD gene in the proband's brother. These findings suggest that the observed compound heterozygosity of the ALAD gene may be responsible for Doss porphyria in the proband. The proband was successfully treated with haem arginate infusion. The clinical condition improved, and urinary excretion of ALA and coproporphyrin fell to levels of approximately 50% compared with their pretreatment levels during acute relapses. The haem therapy was continued once weekly for 1 year. At the end of 1 year, urinary ALA and porphyrin levels were significantly lowered, and the proband is now almost free of clinical symptoms.

2-Methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency is caused by mutations in the HADH2 gene

2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) deficiency is a novel inborn error of isoleucine degradation. In this article, we report the elucidation of the molecular basis of MHBD deficiency. To this end, we purified the enzyme from bovine liver. MALDI-TOF mass spectrometry analysis revealed that the purified protein was identical to bovine 3-hydroxyacyl-CoA dehydrogenase type II. The human homolog of this bovine enzyme is a short-chain 3-hydroxyacyl-CoA dehydrogenase, also known as the "endoplasmic reticulum-associated amyloid-beta binding protein" (ERAB). This led to the identification of the X-chromosomal gene involved, which previously had been denoted "HADH2." Sequence analysis of the HADH2 gene from patients with MHBD deficiency revealed the presence of two missense mutations (R130C and L122V). Heterologous expression of the mutant cDNAs in Escherichia coli showed that both mutations almost completely abolish enzyme activity. This confirms that MHBD deficiency is caused by mutations in the HADH2 gene.