Clinically, porphyrias are classified as (a) acute attacks (neuropsychiatric) only, e.g., acute intermittent porphyria (AIP) and ALA dehydratase
deficiency; (b) cutaneous (photosensitivity), e.g., porphyria cutanea tarda (PCT), congenital erythropoietic porphyria (CEP), and erythropoietic protoporphyria (EPP); (c) both cutaneous disease and acute attacks, e.g., variegate porphyria (VP) and hereditary coproporphyria (HCP).
Lead causes a disruption in heme synthesis by the inhibition of ALA dehydratase
(ALAD), coproporphyrin oxidase, and ferrochelatase.
In LP, the metal directly inhibits the ALA dehydratase
. The result is overproduction of delta-ALA only; PBG normal, reflecting the impaired conversion of delta-ALA to PBG.
(40) in the same group in 1977 found that ALA dehydratase
activity in erythrocytes and liver from patients with HRT was less than 5% and 1% deficient, respectively, compared with controls.
We found deficiencies of ALA dehydratase
that correlates with acute intermittent porphyria, both with neurological symptoms.
Two of the acute porphyrias arise from enzyme deficiencies early in the pathway: ALA dehydratase
(ALAD) in the very rare ALAD deficiency porphyria and PBG deaminase (PBGD) in AIP.
The increased ALA concentrations in AIP may reflect up-regulation of the biosynthetic pathway to compensate for heme deficiency and/or a possible inhibitory effect of PBG on ALA dehydratase
Molecular studies of the gene defect of ALA dehydratase
deficiency porphyria: a new point mutation identified in a second German patient.