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Osteoporosis

Osteoporosis. Excessive skeletal fragility leading to low trauma fractures. Intrinsic skeletal factors: low bone mass, unfavorable geometry at cortical bone sites, small bone size, poor bone structure at cancellous bone sites and sluggish or ineffective repair of microdamage.

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Osteoporosis

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  1. Osteoporosis • Excessive skeletal fragility leading to low trauma fractures. • Intrinsic skeletal factors: low bone mass, unfavorable geometry at cortical bone sites, small bone size, poor bone structure at cancellous bone sites and sluggish or ineffective repair of microdamage. • Extrinsic factors: propensity to fall.

  2. Osteoporosis • 1.7 million hip fractures 1990 • 6.3 million hip fractures 2050 • 40% of postmenopausal women, on average, will suffer at least one osteoporotic fracture • Osteoporosis incurs ~14 billion dollars in the US alone in 1997

  3. WHO Criteria:bone mass values that is >2.5 SD below the young adult mean value. BMD (bone mineral density):measured by techniques such as DXA (dual energy x-ray absorptiometry).

  4. Determination of BMD • By environmental factors(individual factors as well as E x E interaction) (Smoking, nutrition, exercises, diseases, medication, alcohol consumption etc.) ~15-45%. • By genetic factors • (individual genes as well as epistasis) ~55-85%. • By G x E Interaction~ ? %.

  5. Segregation analyses • No major genes: (Guegen et al., 1995); • Major genes: (Livshits et al., 1996; 1999; 2002; Cardon et al., 2000; Deng et al., 2002; Liu et al., 2003a, b).

  6. Genetic correlation • Significant between BMD at different sites (Pocock et al., 1987; Nguyen et al., 1998; Deng et al., 1999; Kobyliansky et al., 2000); • Not significant between BMD and osteoporotic fractures (OF) (Deng et al., 2002). At hip, • h2 BMD: 0.65, h2 OF: 0.53; • genetic correlation between BMD and OF: 0.05.

  7. Goals of Molecular Genetics of Osteoporosis • To identify genes for risk of osteoporotic fractures • develop molecular genetic markers for diagnosis, prevention, early intervention, and individualized treatment • study molecular and cell functions of mutations of genes identified for development of drug and effective treatment

  8. Monogenic bone diseases

  9. Knockout and transgenic mice (1)

  10. Knockout and transgenic mice (2)

  11. Approaches • Association studies • Linkage studies • Transmission Disequilibrium Test (TDT) • QTL mapping in mice • gene expression studies • Proteomics

  12. Association studies in random samples

  13. Linkage studies in pedigrees

  14. Linkage studies in relative pairs

  15. TDT analyses in children from nuclear families

  16. QTL mapping in mice (F2 design)

  17. Candidate Genes Associated with Bone Phenotypes (1)

  18. Candidate Genes Associated with Bone Phenotypes (2)

  19. VDR Gene (12q12-14) • VD modulates intestinal calcium absorption, osteoclastic and osteoblastic activities, PTH production. • VDR mediates the biological actions of 1,25(OH)2D3. • Mutations in VDR gene cause hereditary vitamin D-resistant rickets. • VDR gene knockout mice possess low bone mass, hypocalcemia, and hyperparathyroidism.

  20. Morrison et al. (1994): a significant association between the Bsm I polymorphism and BMD. • Meta-analyses: BMD is associated with VDR gene (Cooper et al., 1996; Gong et al., 1999). Cdx-2 Taq I RFLP

  21. ER-Gene (6q25) • ER-mediates the physiologic effects of the estrogen. • ER- expression found in human osteoblasts and osteoclasts. • Estrogen resistance due to a nonsense mutation in ER- gene causes severe osteoporosis (Smith et al. 1994).

  22. Sano et al. (1995): associations between the TA repeat polymorphism and BMD in Japanese women. • Meta-analysis: Xba I polymorphism is associated with BMD and OF(Ioannidis et al., 2002).

  23. COLIA1 Gene(17q21-q22) • COLIA1 gene encodes the 1(I) protein chain of type I collagen, the most abundant extracellular bone matrix protein. • Mutations in the coding regions of the COLIA1 gene result in osteogenesis imperfecta. • COLIA1 knock-out mice exhibits low bone mass and high risk fractures.

  24. Grant et al. (1996) described an association between a GT polymorphism in a binding motif for Sp1 with BMD and OF. • Meta-analysis: Sp1 polymorphism is associated with BMD and OF (Mann et al., 2001; Efstathiadou et al., 2001). • Sp1 polymorphism may be functional (Mann et al., 2001).

  25. TDT of candidate genes • TGF-1 gene (hip BMD)(Keen et al., 2001); • VDR (hip BMD), BGP (spine BMD) and PTH genes (Deng et al., 2002) • BGP gene (spine BMD and ultrasound measurements of bone) (Andrew et al., 2002); • ER- gene(hip and spine BMD)(Qin et al., 2003).

  26. Interaction studies • ER- and VDR genes for BMD (Willings et al., 1998); • VDR and COL1a1 genes for OF (Uitterlinden et al. 2001); • VDR gene and Ca2+ intake for BMD change (Ferrari et al., 1995; Krall et al., 1995; Kiel et al., 1997); • ER- and VDR genes for BMD change during HRT(Deng et al., 1998).

  27. Genetic basis of racial differentiation • VDR BsmI and hip OF (Young et al., 1996). • Sp1 and RsaI of Col1a1,–174G/C of IL-6, Asn363Ser of GR, and the T->C of TGF- 1(Lei et al., 2002). • BsaHI of CASR, SacI of AHSG, PvuII and XbaI ER-α, ApaI VDR, and BstBI PTH (Dvornyk et al., 2003).

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