Genetic variation in dihydropyrimidine dehydrogenase (DPYD) gene in a healthy adult Indian population.

BACKGROUND: Dihydropyrimidine dehydrogenase (DPD) encoded by DPYD gene is the major enzyme involved in metabolism of 5-flurouracil (5-FU), a pyrimidine analogue used in cancer chemotherapy. Although very effective as a cancer therapeutic drug, if not rapidly metabolized, 5-FU may prove lethal. Single nucleotide variants (SNVs) within DPYD that modulate DPD enzyme activity contribute to 5-FU toxicity. STUDY: This study looked for DPYD SNVs common in the Indian population that might be associated with variable DPD activity and drug toxicity. To achieve this, sequencing analysis was performed of all 23 exons and flanking intronic regions of the DPYD gene in a cohort of 50 healthy adult Indians. This study detected 22 SNVs including intronic, synonymous and non-synonymous changes in the DPYD gene, of which six have not been documented before. Allelic frequency was calculated for the observed variants and linkage disequilibrium (LD) analysis was performed on variants with frequency ≥0.1 to identify haplotypes. CONCLUSIONS: This study provides a brief overview of the genetic polymorphism in DPYD in Indians and emphasizes the need for a large scale extensive study to establish markers associated with the frequently observed variable drug metabolism.

Determination of common genetic variants in cytidine deaminase (CDA) gene in Indian ethnic population.

Cytidine deaminase (CDA) is the major enzyme involved in metabolism of gemcitabine, a pyrimidine analog widely used for chemotherapy of solid tumors. While only low amounts of administered gemcitabine undergo intracellular phosphorylation into active forms and involve in antineoplastic activities, majority of it is rapidly inactivated by CDA and excreted to avoid drug toxicity. Knowledge of the genetic polymorphisms mildly effecting cellular activity of the enzyme CDA is therefore crucial to understanding drug-induced toxicities associated with gemcitabine. Functional significance and allele frequencies for common SNPs including 79A>C (*2) and 208G>A (*3) have been reported in various ethnic populations including Caucasian, African, Korean and Japanese. However, such studies have not been reported in any Indian sub-population. In the present study, conventional polymerase chain reaction (PCR) based amplification using gene specific primers and Sanger sequencing were performed to identify CDA variants in 50 healthy individuals from Indian sub-population. Established common variant 79A>C known to reduce CDA activity was observed at a frequency of 0.14 in the study cohort. In addition to other known variants, one novel variant, c.325-209T>C was detected at a frequency of 0.06. Genetic variants in CDA gene and their frequencies established in our study hold value in pharmacogenetics.

Full-gene-sequencing analysis of N-acetyltransferase-2 in an adult Indian population.

AIMS: Drug-metabolizing enzymes play a major role in determining the outcome of drug therapy. N-acetyltransferase-2 (NAT2) is one of the main enzymes involved in metabolism of isoniazid used in treatment of tuberculosis (TB). Several variations in the NAT2 gene give rise to multiple haplotypes that phenotypically code for different acetylator status. The objective was to generate a more unambiguous picture of the NAT2 scenario in India as compared to that obtained from polymerase chain reaction-restriction fragment length polymorphism methods. METHODS: Full-gene-sequencing analysis of NAT2 was carried out in 181 healthy Indian subjects from different regional groups. RESULTS: A total of 33 diplotypes were recorded from six known single-nucleotide polymorphisms. The overall frequency of the slow acetylator haplotypes detected in this study was 65%, followed by 26% and 9% intermediate and rapid acetylators, respectively. Of the slow acetylator alleles, the NAT2*5B/*6A occurred in 25% of the study subjects. CONCLUSIONS: The study indicates that the frequency of slow acetylator alleles is high in the adult Indian population. Since the prevalence of TB is high in this population, pharmacogenetic testing for NAT2 alleles may be advisable before start of therapy with isoniazid to prevent drug toxicity.

Genotype frequencies of drug-metabolizing enzymes responsible for purine and pyrimidine antagonists in a healthy Asian-Indian population.

Purine and pyrimidine antimetabolites are used to treat leukemias, autoimmune diseases, and solid tumors. Detection of slow metabolizers before administration of the drugs is necessary to prevent any subsequent drug toxicity. With this aim, we determined the frequencies of normal and slow alleles in our population. Polymorphisms in genes encoding cytidine deaminase (CDA), dihydropyrimidine dehydrogenase (DPYD), and thiopurine-S-methyltransferase (TPMT) were documented in 225 healthy volunteers. The polymorphisms typed included CDA*3, DPYD*2A, TPMT*2A, TPMT*3B, and TPMT*3C. Methods used for genotyping included standard PCR-RFLP and allele-specific PCR reactions. The frequencies were 0.44 % for DPYD*2A, 0.67 % for TPMT*3B, and 0.89 % for TPMT*3C. The CDA*3 and TPMT*2A alleles were not detected. Although these polymorphisms have been demonstrated to be associated with drug toxicity in other populations, they appear to be very rare in the adult Indian population.