Is the variant c.422+90G→A in intron 4 of indoleamine 2, 3 -dioxygenase (IDO) gene related to age related cataracts?

PURPOSE: To screen for sequence variations in the IDO gene that encodes indoleamine 2, 3- dioxygenase (IDO), the first rate limiting enzyme involved in the tryptophan catabolism which results in the production of UV filters playing a role in the maintenance of lens transparency. METHODS: We conducted a case-control study to screen for sequence changes in the IDO gene and associated demographic risk factors in patients with nuclear (NC-110), cortical (CC-110) and Posterior sub capsular (PSC-111) cataracts in comparison to normal controls (210) from Hyderabad, India. RESULTS: Among the cataract types studied high risk was observed for CC and PSC types in female patients, individuals with low body mass index and smoking habit. Cataract development had early onset more frequently in cases of PSC followed by CC and NC. Screening by single strand conformation polymorphism (SSCP) revealed mobility shifts in 6 of the 331 patient (3 with NC and 3 with PSC) samples which upon sequencing confirmed the presence of G→A transition (c.422+90G→A; rs4613984) in the intron downstream to exon 4 of IDO which was further tested by RFLP anlaysis using the HhaI restriction enzyme. Of the 6 patients, one with nuclear cataract showed homozygosity and the remaining five showed heterozygosity for the substitution. None of the control samples showed this variation. CONCLUSIONS: It is possible that the substitution c.422+90G→A; rs4613984 in an intron downstream to exon 4 of IDO may be related with cataract formation among the aged.