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.

Osteoporosis 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

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).

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 factorsBy genetic factors (individual genes as well as epistasis) ~ 55-

85%.

By G x E Interaction ~ ? %.

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).

Genetic correlationSignificant 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.

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

Monogenic bone diseasesDisease Gene (Locus) ReferenceOsteopetrosis/renal tubular acidosis Carbonic anhydrase II Nakai et al., 1987Pycnodysostosis Cathepsin K Shi et al., 1995Camurati Engelmann disease TGFβ1 Janssens et al., 2000Osteopetrosis, autosomal recessive TCIRG1 (11q12) Frattini et al., 2000Sclerosteosis/Van Buchem’s disease SOST Balemans et al., 2002Osteoporosis-pseudoglioma LRP-5 (11q12) Gong et al., 2001High bone mass LRP-5 (11q12) Little et al., 2002Osteopetrosis,autosomal dominant CLCN7 Cleiren et al., 2001Osteopetrosis, autosomal recessive CLCN7 Kornak et al., 2001Craniometaphyseal dysplasia, autosomal dominant ANKH Nurnberg et al., 2001Diastrophic dysplasia DTDST Hastbacka et al., 1994Familial expansile osteolysis TNFRSFl1A/RANK Hughes et al., 2000Paget’s disease TNFRSFl1A/RANK Hughes et al., 2000Spondylocostal dystosis, autosomal recessive DLL3 Bulman et al., 2000Oculodentodigital dysplasia 6q22-24 Gladwin et al., 1997Acromegaly 2p-16-12 Gadelha et al., 2000

Knockout and transgenic mice (1)Candidate gene Manipulation Phenotype ReferenceTnrfgf1 1b Knockout Osteoporosis Bucay et al., 1998Tgfb2 Targeted overexpression Osteoporosis Erlebacher et al., 1996K1 Knockout Osteoporosis Kuro-o et al., 1997Abl1 Knockout Osteoporosis Li et al., 2000Lrp5 Knockout Osteoporosis Levasseur et al., 2001Colla1 Mutation Osteopenia, fractures Pereira et al., 1993Colla1 Knock-in mutation Osteopenia, fractures Forlino et al., 1999Colla2 Mutation Osteopenia, fractures Chipman et al., 1993Colla1 Knockout (+/-) Bone fragility Bonadio et al., 1990Tgfb1 Knockout Osteopenia Geiser et al., 1998Nos3 Knockout Osteopenia Aguirre et al., 2001Sparc Knockout Osteopenia Delany et al., 2000Bgn Knockout Osteopenia Xu et al., 1998Mmp 14 Knockout Osteopenia Holmbeck et al., 1999

Knockout and transgenic mice (2)Candidate gene Manipulation Phenotype ReferenceIgf1 Targeted overexpression Increased bone mass Zhao et al., 2000Tgfbr2 Targeted truncation Increased bone mass Filvaroff et al., 1999Vdr Targeted overexpression Increased bone mass Gardiner et al., 2000Lep/lepr Knockout Increased bone mass Ducy et al., 2000Gsn Knockout Increased bone mass Chellaiah et al., 2000Fosl 1 Overexpression Osteoclerosis Jochum et al., 2000Fosb Overexpression Osteoclerosis Sabatakos et al., 2000Traf6 Knockout Osteopetrosis Naito et al., 1999Ctsk Knockout Osteopetrosis Saftig et al., 1998Itgb3 Knockout Osteopetrosis McHugh et al., 2000Fos Knockout Osteopetrosis Wang et al., 1992Tnfrgfl 1a Knockout Osteopetrosis Li et al., 1999TcirgI Knockout Osteopetrosis Li et al., 1999Nfkb1/2 Double knockout Osteopetrosis Iotsova et al., 1997Src Knockout Osteopetrosis Soriano et al., 1991Csf1 Mutation Osteopetrosis Yoshida et al., 1990Sfpi 1 Knockout Osteopetrosis Tondavi et al., 1997Tnfrsfl 1b Overexpression Osteopetrosis Simonet et al., 1997

Approaches

Association studies

Linkage studies

Transmission Disequilibrium Test (TDT)

QTL mapping in mice

gene expression studies

Proteomics

Association studies in random samples

Linkage studies in pedigrees

Linkage studies in relative pairs

TDT analyses in children from nuclear families

QTL mapping in mice (F2 design)

Candidate Genes Associated with Bone Phenotypes (1)

Biological Classification Candidate Gene Chromosome Location ReferenceVDR 12q12-14 Morrison et al., 1994ER- 6q25 Sano et al., 1995ER- 14q22-24 Ogawa et al., 2000CT 11p15 Miyao et al., 2000CTR 7q21 Masi et al., 1998PTH 11p15 Hosoi et al., 1999PTHR1 3p22-21 Minagawa et al., 2002CYP19 15q21 Masi et al., 2001GCCR 5q31 Huizenga et al., 1998CASR 3q13-21 Tsukamoto et al., 2000

Calciotropic hormonesand receptors

AR Xq11-12 Sowers et al., 1999TGF-1 19q13 Langdahl et al., 1997IL-6 7p21 Murray et al., 1997IGF-1 12q22-24 Miyao et al., 1998

Cytokins, growthfactors, and receptors

IL-1RA 2q14 Keen et al., 1998OPG 8q24 Arko et al., 2002TNF- 6p21 Fontova et al., 2002TNFR2 1p36 Spotila et al., 2000

Candidate Genes Associated with Bone Phenotypes (2)

Biological Classification Candidate Gene Chromosome Location ReferenceCOL1A1 17q21-22 Grant et al., 1996COL1A2 7q22 Suuriniemi et al., 2002BGP 1q25-31 Dohi et al., 1998MGP 12p13-12 Tsukamoto et al., 2000

Bone matrix proteins

AHSG 3q27 Dickson et al., 1994ApoE 19q13 Shiraki et al., 1997MTHFR 1p36 Miyao et al., 2000

Miscellaneous

P57(KIP2) 11p15 Urano et al., 2000HLA-A 6p21 Tsuji et al., 1998PPAR- 3p25 Ogawa et al., 1999FRA-1 11q13 Albagha et al., 2002RUNX-2 6p21 Vaughan et al., 2002Klotho gene 13q12 Kawano et al., 2002WRN (Wernersyndrome gene)

8p12-11 Ogata et al., 2001

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.

Taq I RFLP

Cdx-2

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).

ER-ER- Gene Gene (6q25)(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).

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).

COLIA1 GeneCOLIA1 Gene ((17q21-q2217q21-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.

Grant et al. (1996) described an association between a GT 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).

TDT of candidate genesTGF-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).

Interaction studiesInteraction studiesER- 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).

Genetic basis of racial differentiationVDR 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).