Dual gene defects involving δ‐aminolaevulinate dehydratase and coproporphyrinogen oxidase in a porphyria patient

Abstract

Summary A Caucasian male had symptoms of acute porphyria, with increases in urinary δ‐aminolaevulinic acid (ALA), porphobilinogen (PBG) and coproporphyrin that were consistent with hereditary coproporphyria (HCP). However, a greater than expected increase in ALA, compared with PBG, and a substantial increase in erythrocyte zinc protoporphyrin, suggested additional ALA dehydratase (ALAD) deficiency. Nucleotide sequence analysis of coproporphyrinogen oxidase (CPO) cDNA of the patient, but not of the parents, revealed a novel nucleotide transition G835→C, resulting in an amino acid change, G279R. The mutant CPO protein expressed in Escherichia coli was unstable, and produced about 5% of activity compared with the wild‐type CPO. Erythrocyte ALAD activity was 32% of normal in the proband. Nucleotide sequence analysis of cloned ALAD cDNAs from the patient revealed a C36→G base transition (F12L amino acid change). The F12L ALAD mutation, which was found in the mother and a brother, was previously described, and is known to lack any enzyme activity. This patient thus represents the first case of porphyria where both CPO and ALAD deficiencies were demonstrated at the molecular level.

Digenic Inheritance of Mutations in the Coproporphyrinogen Oxidase and Protoporphyrinogen Oxidase Genes in a Unique Type of Porphyria

“…These results were based mainly on biochemical and enzymatic studies, and only in two instances they were confirmed by molecular genetic analysis (Akagi et al, 2006;Harraway et al, 2006;Poblete Gutierrez et al, 2006). To our knowledge, the constellation of digenic mutations in the CPOX and PPOX genes has not yet been reported.…”

“…By contrast, in the two patients with the other genetically confirmed dual porphyrias, the clinical phenotype was heterogeneous, with one patient experiencing only cutaneous symptoms and the other showing signs of an acute porphyric attack (Akagi et al, 2006;Harraway et al, 2006). The heterogeneous clinical phenotypes observed in our index patient and the two individuals with dual porphyria support the current notion that there is little evidence for genotype-phenotype correlations either in the common types of porphyria, which can be inherited in an autosomal dominant or recessive manner, or in the rare patients with dual porphyrias.…”

“…These techniques, however, may be insufficient in diagnosing rare patients with dual porphyria (Akagi et al, 2006;Poblete Gutierrez et al, 2006). The index patient (individual II-5 in Figure 1b) repeatedly showed a biochemical profile suggesting HCP, with fecal coproporphyrin concentrations higher than those of protoporphyrin.…”

Clinical and Laboratory Diagnosis of the Porphyrias

“…[30][31][32][33][34][35][36] Cases termed dual porphyria have genetic alterations of two heme pathway enzymes, which can be suspected based on unusual combinations of biochemical features and then confirmed by DNA studies for identification of dual mutations. [37][38][39] …”

Hereditary cataract of the Nakano mouse: Involvement of a hypomorphic mutation in the coproporphyrinogen oxidase gene

“…PCR was used to amplify Cpox cDNA fragments from mice, which were subsequently inserted into the NdeI/XhoI site of the pET-21a(+) plasmid. Bacterial expression and purification of recombinant mouse CPOX were performed as previously described for human CPOX (Akagi et al, 2005) with modifications.…”