The parathyroid hormone type 1 receptor (PTHR1) mediates the actions of parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHRP). Interacting with this receptor, PTHRP contributes to skeletal development through the regulation of chondrocyte proliferation and differentiation. Recently, a tetranucleotide repeat - (AAAG)n - In the P3 promoter of the PTHR1 gene has been shown to have functional activity in vitro, and homozygosity for (AAAG)6, or the 6/6 genotype, has been associated with greater adult height compared to the 5/5 genotype. In this study, we evaluated the association of (AAAG)n with height and bone mineral density (BMD) measured at lumbar spine (LS) and femoral neck (FN) in a cohort of 677 young caucasian women 18-35 years of age. Genomic DNA was amplified and genotyped by comparison with sequenced controls following electrophoretic separation through high-resolution polyacrylamide gels. Allele frequencies for (AAAG)n were: 76.8% (n=5); 20.9% (n=6); 1.8% (n=7); 0.18% (n=8); 0.27% (n=9); 0.08% (n=2), and there was no evidence for Hardy-Weinberg disequilibrium. Analysis of variance showed that subjects bearing one or two (AAAG)6 alleles (6/X & 6/6) were significantly taller (165.7±0.5 cm) than the others (X/X, 164.5±0.3 cm; P=0.034). This association was significant after adjusting for multiple covariates-current age, age at menarche, physical activity, smoking status, and intakes of caffeine and calcium. Comparison of genotype groups for BMD was not significant at LS, but BMD was significantly higher at FN in the group with at least one (AAAG)6 allele (adjusted means: 1.021±0.008 vs. 0.999±0.006 g/cm2, P=0.032). In conclusion, our data show that subjects bearing one or two (AAAG)6 alleles are taller than subjects without, reinforcing the notion that in vivo variation in promoter activity of the PTHR1 gene may be a relevant genetic influence on final adult height and BMD.
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