title: Analysis of ITPA phenotype-genotype correlation in the Bulgarian population revealed a novel gene variant in exon 6.
abstract: Mutations in the inosine triphosphate pyrophosphohydrolase (ITPA) gene causing enzyme deficiency were shown to have pharmacogenetic implications in azathioprine-induced adverse drug reactions. The distribution of ITPA activity as well as the types and the frequencies of gene variants associated with a lower enzyme activity were determined in healthy volunteers from a Bulgarian population. The ITPA activity was measured in 185 erythrocyte samples by an established high-performance liquid chromatography procedure. All samples were genotyped for 94C > A, IVS2 + 21A > C, and IVS2 + 68T > C/G by real-time polymerase chain reaction with hybridization probes. The ITPA activity ranged from 7.5 to 587.8 micromoL IMP/(g Hb x h) with a median value of 162.9 micromoL IMP/(g Hb x h). The enzyme activity showed significant differences between females and males (P = 0.006) with 17% higher values in men than women. Mutant allele frequencies were 0.038 (94C > A) and 0.130 (IVS2 + 21A > C). Mutations at IVS2 + 68 were not identified. Using a cutoff at 75 micromoL IMP/(g Hb x h) phenotyping detected all heterozygous carriers of 94C > A, two compound heterozygotes, all IVS2 + 21A > C homozygotes and 12.5% of IVS2 + 21A > C heterozygous cases. A novel frameshift mutation 359_366dupTCAGCACC in exon 6 was found in a subject with reduced enzyme activity of 61.2 micromoL IMP/(g Hb x h). The interindividual variability in ITPA activity among the Bulgarian population resembles the distribution of enzyme activity in other whites, although the observed median activity was approximately 25% lower in the Bulgarians [163 vs 219 micromoL IMP/(g Hb x h)]. The most common mutant allele IVS2 + 21A > C showed a similar frequency like in other white populations, whereas the 94C > A mutation was less frequently observed compared with other whites. Heterozygosity for the novel gene variant 359_366dupTCAGCACC was associated with 30% enzyme activity of the wild-type median value. The role of this rare variant for the thiopurine intolerance is not explored. These data further extend the knowledge for ITPA heterogeneity in whites.
authors.affiliation: Department of Clinical Chemistry, Georg-August University Goettingen, Goettingen, Germany. atanasova@med.uni-goettingen.de
authors.forename: Srebrena
authors.initials: S
authors.lastname: Atanasova
authors.forename: Maria
authors.initials: M
authors.lastname: Shipkova
authors.forename: Dobrin
authors.initials: D
authors.lastname: Svinarov
authors.forename: Antoaneta
authors.initials: A
authors.lastname: Mladenova
authors.forename: Mariana
authors.initials: M
authors.lastname: Genova
authors.forename: Eberhard
authors.initials: E
authors.lastname: Wieland
authors.forename: Michael
authors.initials: M
authors.lastname: Oellerich
authors.forename: Nicolas
authors.initials: N
authors.lastname: von Ahsen
mesh_terms: D000293:Adolescent; D000328:Adult; D001379:Azathioprine / Q000378:metabolism / Q000627:therapeutic use; D001483:Base Sequence; D002031:Bulgaria; D002851:Chromatography, High Pressure Liquid; D004912:Erythrocytes / Q000187:drug effects / Q000201:enzymology; D005091:Exons / Q000235:genetics*; D005260:Female; D005787:Gene Frequency; D005838:Genotype; D006801:Humans; D007291:Inosine Monophosphate / Q000097:blood / Q000378:metabolism; D008297:Male; D015122:Mercaptopurine / Q000378:metabolism / Q000627:therapeutic use; D008875:Middle Aged; D009154:Mutation; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D011755:Pyrophosphatases / Q000235:genetics* / Q000378:metabolism; D012737:Sex Factors; D000097630:Inosine Triphosphatase
chemical_list: D001379:Azathioprine; D007291:Inosine Monophosphate; D015122:Mercaptopurine; D011755:Pyrophosphatases; D000097630:Inosine Triphosphatase