The purpose of this paper is to report the linkage of a genetic locus (designated 'HBM') in the human genome to a phenotype of very high spinal bone density, using a single extended pedigree. We measured spinal bone mineral density, spinal Z(BMD), and collected blood from 22 members of this kindred. DNA was genotyped on an Applied Biosystems model 377 (ABI PRISM Linkage Mapping Sets; Perkin Elmer Applied Biosystems), by use of fluorescence-based marker sets that included 345 markers. Both two-point and multipoint linkage analyses were performed, by use of affected/unaffected and quantitative-trait models. Spinal Z(BMD) for affected individuals (N = 12) of the kindred was 5.54 ± 1.40; and for unaffected individuals (N = 16) it was 0.41 ± 0.81. The trait was present in affected individuals 18-86 years of age, suggesting that HBM influences peak bone mass. The only region of linkage was to a series of markers on chromosome 11 (11q12-13). The highest LOD score (5.21) obtained in two-point analysis, when a quantitative-trait model was used, was at D11S987. Multipoint analysis using a quantitative- trait model confirmed the linkage, with a LOD score of 5.74 near marker D11S987. HBM demonstrates the utility of spinal Z(BMD) as a quantitative bone phenotype that can be used for linkage analysis. Osteoporosis pseudoglioma syndrome also has been mapped to this region of chromosome 11. Identification of the causal gene for both traits will be required for determination of whether a single gene with different alleles that determine a wide range of peak bone densities exists in this region.
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