Background: Acute intermittent porphyria (AIP) is an metabolic disorder characterized by a partial deficiency of the porphobilinogen deaminase, the enzyme of heme biosynthesis. The metabolic defect in AIP involves an approximately half-normal activity of porphobilinogen deaminase (PBGD, EC 4.3.1.8), the enzyme catalyzing condensation of four porphobilinogen molecules to hydroxymethylbilane. Due to tissue-specific alternative transcript splicing, the PBGD gene mutations within the range of exons 3-15 may lead to classical AIP involving erythrocytes and all the other tissues. Mutations within intron and exon 1 may result in the so-called non-erythroid AIP in which the PBGD activity is normal in erythrocytes and diminished in other tissues.
Objectives: The aim of the present study was to characterise molecular errors in the PBGD gene in Polish patients with non-erythroid AIP and to evaluate the efficacy of the DNA sequencing method in the early diagnosis of this disorder.
Material and methods: Twenty five members of nine non-erythroid AIP families were assessed. In each of them DNA sequencing was performed using the Big Dye Terminator Cycle Sequencing Kit v.1.1 on the Hitachi 3730 Analyzer (Applied Biosystem, USA).
Results: Four mutations were detected in intron 1 of the PBGD gene, including one unreported novel mutation, 33+(4-12) del AGTGCTGAG, of an unknown biological mechanism, and three previously described mutations, i.e. 33+1 G > A, 33+2 T > C, 33+5 G > C, responsible for abnormal transcript splicing in the area of exon 1. Of 14 asymptomatic members of proband families in 6 subjects were diagnosed with AIP, and in 8 the AIP was excluded based on the DNA sequencing method.
Conclusions: DNA sequencing based analysis is the only reliable method for correct diagnosis of asymptomatic non-erythroid AIP patients with normal urinary excretion of heme precursors. The mutations found in Polish patients with non-erythroid AIP represented those of splice defect and resulted in abnormal exon 1 splicing.