1. ¹Engelhardt Institute of Molecular Biology of the Russian Academy of Sciences, Moscow, Russia
2. ²Research Institute of Pediatric Hematology, Moscow, Russia
3. ³St Jude Children's Research Hospital, Memphis, TN, USA
4. ⁴University of Tennessee, Memphis, TN, USA

Correspondence: Dr TV Nasedkina, Engelhardt Institute of Molecular Biology, 32 Vavilov St, Moscow 119991, Russia. Tel: +7 095 135 6259; Fax: +7 095 135 1405; E-mail: nased@eimb.ru

Received 10 November 2005; Revised 27 February 2006; Accepted 28 March 2006; Published online 17 May 2006.

Abstract

Thiopurine drugs are metabolized, in part, by S-methylation catalyzed by thiopurine S-methyltransferase (TPMT). Patients with very low or undetectable TPMT activity are at high risk of severe, potentially fatal hematopoietic toxicity when they are treated with standard doses of thiopurines. As human TPMT activity is controlled by a common genetic polymorphism, it is an excellent candidate for the clinical application of pharmacogenetics. Here, we report a new molecular approach developed to detect point mutations in the TPMT gene that cause the loss of TPMT activity. A fluorescently labeled amplified DNA is hybridized with oligonucleotide DNA probes immobilized in gel pads on a biochip. The specially designed TPMT biochip can recognize six point mutations in the TPMT gene and seven corresponding alleles associated with TPMT deficiency: TPMT^*2; TPMT^*3A, TPMT^*3B, TPMT^*3C, TPMT^*3D, TPMT^*7, and TPMT^*8. The effectiveness of the protocol was tested by genotyping 58 samples of known genotype. The results showed 100% concordance between the biochip-based approach and the established PCR protocol. The genotyping procedure is fast, reliable and can be used for rapid screening of inactivating mutations in the TPMT gene. The study also provides the first data on the frequency of common TPMT variant alleles in the Russian population, based on a biochip analysis of 700 samples. TPMT gene mutations were identified in 44 subjects; genotype *1/*3A was most frequent.