Bone mineral densities in individuals with Gilbert's syndrome: a cross-sectional, case-control pilot study.

BACKGROUND: Unconjugated bilirubin inhibits osteoblastic proliferative activity in vitro, raising the possibility that Gilbert's syndrome (GS) patients are at increased risk of osteoporosis. OBJECTIVES: To compare bone mineral density (BMD), serum parathyroid hormone (PTH), C-telopeptide (CTX) and osteocalcin levels in GS subjects versus matched controls in a cross-sectional, case-control study. METHODS: BMD determinations were obtained with central dual energy x-ray absorptiometry. Serum PTH, CTX and osteocalcin levels were measured by enzyme immunoassay. RESULTS: A total of 17 GS and 30 control subjects were studied. Overall, there were no significant differences in BMD, PTH, CTX or osteocalcin levels between the two groups. However, when older (older than 40 years of age) and younger (40 years of age and younger) cohorts were considered separately, the older GS cohort had significantly decreased total hip BMD, T scores and Z scores, and femoral neck BMD, T scores and Z scores (P<0.005 for each parameter, respectively) compared with older control subjects. Serum osteocalcin levels were lower in the older versus younger GS cohort (P=0.006). An inverse correlation existed between all subjects' serum unconjugated bilirubin levels and total body BMD determinations (r=-0.42; P=0.04). On univariate analysis, the association between serum unconjugated bilirubin and total body BMD was not significant (P=0.066), nor was serum unconjugated bilirubin identified as a risk factor for low BMD when entered into multivariate analyses. CONCLUSIONS: The results of the present pilot study warrant further research involving larger numbers of subjects and longitudinal measurements to determine whether GS is associated with decreased BMD, particularly in older GS subjects.