Polymorphisms in the low-density lipoprotein receptor-related protein 5 (LRP5) gene are associated with variation in vertebral bone mass, vertebral bone size, and stature in whites

Abstract

Stature, bone size, and bone mass are interrelated traits with high heritability, but the major genes that govern these phenotypes remain unknown. Independent genomewide quantitative-trait locus studies have suggested a locus for bone-mineral density and stature at chromosome 11q12-13, a region harboring the low-density lipoprotein receptor-related protein 5 (LRP5) gene. Mutations in the LRP5 gene were recently implicated in osteoporosis-pseudoglioma and "high-bone-mass" syndromes. To test whether polymorphisms in the LRP5 gene contribute to bone-mass determination in the general population, we studied a cross-sectional cohort of 889 healthy whites of both sexes. Significant associations were found for a missense substitution in exon 9 (c.2047G-->A) with lumbar spine (LS)-bone-mineral content (BMC) (P=.0032), with bone area (P=.0014), and with stature (P=.0062). The associations were observed mainly in adult men, in whom LRP5 polymorphisms accounted for <or=15% of the traits' variances. Results of haplotype analysis of five single-nucleotide polymorphisms in the LRP5 region suggest that additional genetic variation within the locus might also contribute to bone-mass and size determination. To confirm our results, we investigated whether LRP5 haplotypes were associated with 1-year gain in vertebral bone mass and size in 386 prepubertal children. Significant associations were observed for changes in BMC (P=.0348) and bone area (P=.0286) in males but not females, independently supporting our observations of a mostly male-specific effect, as seen in the adults. Together, these results suggest that LRP5 variants significantly contribute to LS-bone-mass and size determination in men by influencing vertebral bone growth during childhood.

Figure 1

Schematic diagram of SNP localization in LRP5. Vertical bars represent the 23 exons of LRP5, and arrows indicate the positions of the eight validated SNPs with a minimum allele frequency of 2%. SNPs encoding missense substitutions are boxed. Leading asterisks (*) indicate SNPs used in the association study. Percentages indicate the frequency of the rare allele. The insert shows LD for all SNP pairs, calculated as R² values. Gray-shaded coding represents the strength of LD (R² values), according to the scale shown on the left. Leading asterisks (*) inside the boxes indicate the level of significance for LD; one asterisk (*) denotes P=.01 to .001, and two asterisks (**) denotes P<.001.

Figure 2

Differences in adult LS bone measurements and stature, according to LRP5 exon 9 missense SNP and sex. Stature and aBMD, BMC, and bone area at the LS were measured cross-sectionally in 364 adult subjects of both sexes. Results are mean Z scores ± SEM adjusted for age and sex. Only significant P values (measured by ANCOVA), with weight as covariate, within sexes are shown.

Figure 3

Differences in adult LS measurements, according to LRP5 haplotypes. aBMD, BMC, and bone area at the LS were measured cross-sectionally in men and women and were expressed as standardized Z scores (±SE). Haplotypes were based on SNPs c.1980, c.2047, c.3405, and c.4037, as detailed in table 3. Sizes for haplotype groups in adults of both sexes (panel A) are as follows: 0,0 n=156; 0,1 n=21; 0,2 n=50; 0,3 n=39; 2,1 n=4; 2,2 n=5; 3,1 n=2; 3,2 n=5; 3,3 n=2; 4,0 n=44; 4,1 n=5; 4,2 n=7; 4,3 n=4. Group sizes for the reduced haplotype combinations in female/male (females indicated by blackened circles; males indicated by unblackened squares) (panel B) are as follows: 0′,0′ (0′=2047G-4037C), n=133/112; 0′,3 (3=2047G-4037T), n=29/19; 0′,4 (4=2047A-4037T), n=31/27. P values for overall differences between haplotype groups were calculated by use of ANCOVA, with weight as a covariate.

Figure 4

Changes in LS bone size and mass during childhood, according to LRP5 exon 9 c.2047 genotypes and haplotypes. Mean changes (±SEM) in LS BMC and projected area were evaluated between baseline and 1 year in prepubertal males (M) and females (F). Panel A shows mean changes according to c.2047 genotypes, panel B according to reduced haplotype combinations, as in figure 3B. The number of females/males in each group is as follows: 0′,0′, n=109/168; 0′,3, n=22/38; 0′,4, n=16/29. Significant P values for differences between exon 9 genotypes and between haplotypes 3 and 4 are shown.