Microarray with LNA-probes for genotyping of polymorphic variants of Gilbert's syndrome gene UGT1A1(TA)n

Gilbert's syndrome is a common metabolic dysfunction characterized by elevated levels of unconjugated bilirubin in the bloodstream. This condition is usually caused by additional (TA) insertions in a promoter region of the uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene, which instead of the sequence А(TА)6TАА contains А(TА)7TАА. While the condition itself is benign, it presents elevated risk for patients treated with irinotecan, a common chemotherapy drug.

The technique is based on hybridization analysis of a pre-amplified segment of the UGT1A1 gene promoter performed on a microarray. Specific probes containing locked nucleic acids (LNA) were designed and immobilized on the microarray to provide accurate identification.

A microarray has been developed to identify both common and rare variants of UGT1A1(TA)n polymorphisms. In total, 108 individuals were genotyped. Out of these, 47 (43.5%) had homozygous wild-type genotypes (TA)6/(TA)6; 41(38%) were heterozygotes (TA)6/(TA)7; and 18 (16.7%)--homozygotes (TA)7/(TA)7. In two cases (1.8%), rare genotypes (TA)5/(TA)7 and (TA)5/(TA)6 were found. The results were in full agreement with the sequencing. In addition, synthetic fragments corresponding to all human allelic variants [(TA)5, (TA)6, (TA)7, (TA)8] were successfully tested.

The developed microarray-based approach for identification of polymorphic variants of the UGT1A1 gene is a promising and reliable diagnostic tool that can be successfully implemented in clinical practice.