Collagen type Ialpha1 and vitamin D receptor gene polymorphisms and bone mass in primary biliary cirrhosis

The potential influence of two gene polymorphisms, vitamin D receptor gene (VDR) and the gene encoding collagen type Ialpha1 (COLIA1) Sp1 polymorphisms, in the reduced bone mass observed in patients with primary biliary cirrhosis (PBC) was assessed in 61 women with PBC (age, 54.1 +/- 1.1 years) by restriction enzyme digestion of polymerase chain reaction (PCR)-amplified DNA extracted from whole blood. Bone mineral density (BMD) of the lumbar spine (L2-L4) and proximal femur were measured by X-ray absorptiometry. The severity of liver disease and cholestasis was also evaluated, and changes in BMD were calculated after a mean period of 2.9 +/- 0.3 years in 41 patients. Sixteen patients (26 %) had the BB, 20 the bb (33 %), and 25 Bb (41%) VDR genotypes. There were no significant baseline BMD differences among the 3 VDR genotypes. Forty-one patients (68%) had the SS, 16 the Ss (27%), and 3 the ss (5%) COLIA1 genotypes. The baseline lumbar BMD was significantly lower in patients having the s allele than in the homozygote SS patients (Z-score, -0.76 +/- 0.24 vs. -0.10 +/- 0.17, P =.02). The severity of cholestasis was not related to the VDR or COLIA1 1 polymorphisms. Lumbar bone loss was independent of VDR and COLIA1 genotypes, but it was associated with cholestasis. In conclusion, the COLIA1 but not VDR polymorphism is a genetic marker of peak bone mass in patients with PBC, although the severity of cholestasis is the main factor for osteoporosis since it is associated with the rate of bone loss.