TGFB1 and oral submucous fibrosis: Based on PCR-based restriction fragment length polymorphism assays, a comparative study with 166 patients with oral submucous fibrosis and 284 betel quid chewers reported the highest genotypes of oral submucous fibrosis risk for collagen 1A1, collagen 1A2, collagenase-1, transforming growth factor beta1, lysyl oxidase and cystatin C were CC, AA, TT, CC, AA and AA, respectively, in the low-exposure group.