The porphyrias arise from predominantly inherited catalytic deficiencies of specific enzymes in heme biosynthesis. All genes encoding these enzymes have been cloned and several mutations underlying the different types of porphyrias have been reported. Traditionally, the diagnosis of porphyria
is made on the basis of clinical symptoms, characteristic biochemical findings, and specific enzyme assays. In some cases however, these diagnostic tools reveal overlapping findings, indicating the existence of dual porphyrias with two enzymes of heme biosynthesis being deficient simultane-ously. Recently, it was reported that the so-called Chester porphyria shows features of both variegate porphyria and acute intermittent porphyria. Linkage analysis revealed a novel chromosomal locus on chromosome 11 for the underly-ing genetic defect in this disease, suggesting that a gene that does not encode one of the enzymes of heme biosynthesis might be involved in the pathogenesis of the porphyrias. After excluding candidate genes within the linkage interval, we identified a nonsense mutation in the porphobilinogen deaminase gene on chromosome 11q23.3, which harbors the mutations causing acute intermittent porphyria, as the underlying genetic defect in Chester porphyria. However, we could not detect a mutation in the coding or the promotor region of the protoporphyrinogen oxidase gene that is mutated
in variegate porphyria. Our results indicate that Chester porphyria is neither a dual porphyria, nor a separate type of porphyria, but rather a variant of acute intermittent porphyria. Further, our findings largely exclude the possibility that a hitherto unknown gene is involved in the pathogenesis of the porphyrias.
The porphyrias are heterogeneous disorders arising from predominantly inherited catalytic deficiencies of specific enzymes along the heme biosynthetic pathway. Congenital erythropoietic porphyria is a very rare disease that is inherited as an autosomal recessive trait and results from a profound deficiency of uroporphyrinogen III cosynthase, the fourth enzyme in heme biosynthesis. The degree of severity of clinical symptoms mainly depends on the amount of residual uroporphyrinogen III cosynthase activity. In this study, we sought to characterize the molecular basis of congenital erythropoietic porphyria in Germany by studying four patients with congenital erythropoietic porphyria and
their families. Using PCR-based techniques, we identified four different mutations: C73R, a well-known hotspot mutation, the promoter mutation –86A that was also described previously, and two novel missense mutations, designated G236V and L237P, the latter one encountered in the homozygous state in one of the patients. Our data from the German population further emphasize the molecular heterogeneity of congenital erythropoietic porphyria as well as the advantages of molecular genetic techniques as a diagnostic tool and for the detection of clinically asymptomatic heterozygous mutation carriers within families.