Three novel mutations in porphobilinogen deaminase gene identified in Russian patients with acute intermittent porphyria

Porphobilinogen deaminase (PBGD) is a key enzyme of the heme biosynthetic p athway. Defects in the PBGD gene lead to an autosomal dominant disease, acu te intermittent porphyria (AIP). Almost all AIP patients with rare exceptio ns are heterozygous for the defective gene. To date, at least 160 different mutations causing AIP are identified. Extensive investigations along this line are conducted in many countries of the world. In Russia these studies had not been hitherto performed. Here we report the results of molecular ge netic examination of four Russian patients with AIP diagnosed from clinical symptoms. By direct sequencing of the PBGD gene or the corresponding cDNA, we have detected four mutations, three of which were not previously encoun tered in the world population. These are TAAG deletion in intron 7 between positions +2 and +5 (IVS7 2-5 delTAAG); T deletion in the initiation codon ATG of exon 3, and the G for C replacement at position -1 of intron 5 (IVS5 as -1 G-Q, which disrupts splicing. In addition, in one female patient, a known deletion CT in codon 68 was revealed. In two patients, expression of PBGD gene alleles was significantly disproportional, so that normal mRNA pr evailed in one case and mutant mRNA of nonerythroid type in the other. Dele tion in intron 7 was easily detectable due to the formation of a heterodupl ex fragment with abnormal electrophoretic mobility directly in PCR. This si mple heteroduplex, analysis allowed us to exclude AIP carriage in son and d aughter of a female patient with the genetic defect.