PPIG and osteoporosis: Several pathways were involved in long-chain fatty acid metabolism, largely driven by a cluster of cytochrome P450 (CYP) genes at a single locus (signal 21), which also harbors TGFB1. Although TGFB1 is a plausible candidate gene, CYP genes metabolize eicosanoids (long-chain fatty acids) including arachidonic acid and affect metabolite levels [66], and genetic variation in related genes (CYP-17 and 19) was associated with serum sex steroid concentrations and BMD, osteoporosis, and fracture in post-menopausal women [67].