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Harderoporphyria: a variant hereditary coproporphyria.

Y Nordmann, B Grandchamp, H de Verneuil

    The Journal of Clinical Investigation
    |September 1, 1983
    PubMed
    Summary

    Three siblings presented with severe jaundice and hemolytic anemia due to a rare genetic disorder. This study identifies a novel variant of coproporphyrinogen oxidase deficiency, termed "harderoporphyria," characterized by unique porphyrin excretion patterns.

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    Area of Science:

    • Biochemistry
    • Genetics
    • Metabolic Disorders

    Background:

    • Hereditary coproporphyria (HCP) is a rare genetic disorder affecting heme biosynthesis.
    • It is typically caused by mutations in the *CPOX* gene, leading to reduced activity of coproporphyrinogen III oxidase.
    • Clinical manifestations of HCP can vary, including neurological symptoms and photosensitivity.

    Observation:

    • Three siblings presented with severe neonatal jaundice and hemolytic anemia.
    • Their urine and feces showed high levels of coproporphyrin, with harderoporphyrin being the predominant fecal porphyrin (>60%).
    • Lymphocyte coproporphyrinogen III oxidase activity was significantly reduced (10% of control values) in the affected siblings, suggesting homozygosity.

    Findings:

    • Enzyme kinetics revealed a 15-20-fold higher Michaelis constant and half the maximal velocity for coproporphyrinogen III oxidase in patients.
    • The enzyme also showed increased sensitivity to thermal denaturation.
    • Experiments indicated that both coproporphyrinogen and harderoporphyrinogen are metabolized at the same active center, ruling out a mutation specific to the second decarboxylation step.

    Implications:

    • The distinct porphyrin excretion pattern and enzyme characteristics differentiate this condition from previously described homozygous HCP cases.
    • This study proposes a new classification for this specific enzyme defect: "harderoporphyria."
    • Understanding this variant contributes to the broader knowledge of heme biosynthesis disorders and their genetic underpinnings.