Porphyrias are diverse disorders that arise from various inherited enzyme defects in the heme biosynthesis pathway, except for porphyria cutanea tarda (PCT), in which the enzyme deficiency in most cases is acquired. The biosynthetic blocks resulting from the defective enzymes are largely expressed either in the liver or bone marrow, the sites where the majority of heme is produced. Although the pathophysiologic mechanisms of the clinical manifestations of the porphyrias are not fully understood, two cardinal features prevail: skin photosensitivity and neurologic symptoms of intermittent autonomic neuropathy, acute neurovisceral attacks, and disorders of the nervous system. The primary diagnosis of the proband is based on biochemical testing, which is not always able to identify acute porphyrias, especially in asymptomatic family carriers when heme precursors and porphyrins excretion is normal, low-normal and high-reduced values of enzyme activity overlap, and hematological diseases responsible for abnormal blood cells distribution coexist. Molecular analysis of gene mutations responsible for each type of porphyria is the best diagnostic approach for symptomatic as well as presymptomatic gene carriers (Adv Clin Exp Med 2016, 25, 2, 361-368).

Acute intermittent porphyria (AIP), an autosomal dominant disorder of heme biosynthesis, is due to mutations in hydroxymethylbilane synthase (HMBS; or porphobilinogen deaminase, PBGD) gene. In this study, we analyzed 20 Polish patients affected by AIP and we were able to characterize seven novel mutations. A nonsense mutation (Y46X), two frameshift mutations (315delT and 552delT) and a 131bp deletion (nucleotides 992-1123) give rise to truncated proteins. A donor splice site mutation IVS12+2T>C predicts skipping of exon 12. A missense mutation (D61Y) was identified in two apparently unrelated patients with a clearly clinical indication of AIP. An inframe 3-bp deletion (278-280delTTG) results in the removal of V93 from the enzyme. In addition to the novel mutations, nine previously described HMBS gene mutations-R26H, G111R, IVS7+1G>A, R149X, R173Q, 730-731delCT, R225X, 982-983delCA and G335D-were identified in this cohort. Our results demonstrate that molecular analysis of the PBGD gene is a more reliable method comparing to enzymatic assay in the diagnosis of AIP. Although more than 170 different mutations are known to the HMBS gene so far, over 40% of all mutations identified among the Polish AIP patients of this study are novel mutations, indicating the heterogeneity of molecular defects causing AIP.

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 (Adv Clin Exp Med 2015, 24, 1, 63-68).