Decreased bone mineral density in Prader-Willi syndrome: Comparison with obese subjects

Bone density, anthropometric data, and markers of bone turnover were collec ted on 21 subjects diagnosed with Prader-Willi syndrome (PWS) and compared with 9 subjects with obesity of unknown cause. In addition, urinary N-telop eptide levels were obtained in all subjects. N-telopeptides are the peptide fragments of type I collagen, the major bone matrix material. During perio ds of active bone degradation or high bone turnover, high levels of N-telop eptides are excreted in the urine. However, no significant difference was d etected in the urinary N-telopeptide levels when corrected for creatinine e xcretion (raw or transformed data) between our subjects with obesity or PWS and the observed effect size of the between-group difference was small. Al though N-telopeptide levels were higher but not significantly different in the subjects with PWS compared with obese controls, the subjects with PWS h ad significantly decreased total bone and spine mineral density and total b one mineral content (all P < 0.001). No differences in N-telopeptide levels or bone mineral density were observed between subjects with PWS and chromo some 15q deletion or maternal disomy. Thus, decreased bone mineral density in subjects with PWS may relate to the lack of depositing bone mineral duri ng growth when bones are becoming more dense (e.g., during adolescence), po ssibly because of decreased production of sex or growth hormones and/or lon g-standing hypotonia. It may not be caused by loss, or active degradation, of bone matrix measurable by the methods described in this study further su pporting the possible need for hormone therapy during adolescence. (C) 2001 Wiley-Liss, Inc.