HPRT1 and Behcet disease: In one study Ward et al. (2001) divided the BD-exposed subjects into subgroups according to smoking status and found that the MF of the HPRT gene was significantly higher in the high-exposure nonsmokers (8.64 ± 1.6 × 10−6) than in the low-exposure nonsmokers (3.46 ± 0.65 × 10−6).