Genetic influences in end-stage osteoarthritis. Sibling risks of hip and knee replacement for idiopathic osteoarthritis

Pathogenesis and management of pain in osteoarthritis

The term osteoarthritis describes a common, age-related, heterogeneous group of disorders characterised pathologically by focal areas of loss of articular cartilage in synovial joints, associated with varying degrees of osteophyte formation, subchondral bone change, and synovitis. Joint damage is caused by a mixture of systemic factors that predispose to the disease, and local mechanical factors that dictate its distribution and severity. Various genetic abnormalities have been described, but most sporadic osteoarthritis probably depends on minor contributions from several genetic loci. Osteoarthritic joint damage may be associated with clinical problems, but the severity of joint disease is only weakly related to that of the clinical problem. For this reason the associations and pathogenesis of pain are in as much need of investigation as joint damage. Subchondral bone and synovium may be responsible for nociceptive stimuli, and peripheral neuronal sensitisation is an important feature, and can result in normal activities (such as walking) causing pain. Central pain sensitisation can also occur, and psychosocial factors are important determinants of pain severity. We present a stepwise approach to the management of osteoarthritis.

Genetic mechanisms of knee osteoarthritis: a population based case-control study

OBJECTIVE

To compare subjects who had at least one parent with a total knee replacement for severe primary knee osteoarthritis with age and sex matched controls who had no family history of knee osteoarthritis

DESIGN

Population based case-control study of 188 matched pairs (mean age 45 years, range 26 to 60).

METHODS

Articular cartilage volume and bone size were determined at the patella and at the medial tibial and lateral tibial compartments by processing images acquired using T1 weighted, fat saturated magnetic resonance imaging. Radiographic osteoarthritis (ROA) was assessed from a standing semiflexed radiograph scored for joint space narrowing and osteophytosis. Knee pain was assessed by questionnaire. Height, weight, body mass index (BMI), lower limb muscle strength, and endurance fitness were measured by standard protocols.

RESULTS

Compared with the controls, index offspring had higher BMI (27.8 v 26.0 kg/m(2), p = 0.02), weaker lower limb muscles (127 v 135 kg, p = 0.006), more knee pain (47% v 22%, p<0.001), and greater medial tibial bone area (17.6 v 17.1 cm(2), p = 0.01). With the exception of BMI, these differences persisted in multivariate analysis. There was a non-significant trend to higher cartilage volume at tibial sites and increased ROA in the offspring in the total and subgroup analyses, but no difference in height and endurance fitness.

CONCLUSIONS

BMI, muscle strength, knee pain, and medial tibial bone area, but not cartilage volume, appear to play a role in the genetic regulation and development of knee osteoarthritis.

Evidence for familial aggregation of hand, hip, and spine but not knee osteoarthritis in siblings with multiple joint involvement: the GARP study

OBJECTIVE

To evaluate whether familial aggregation of osteoarthritis differs by joint site in a sibling pair study (GARP) of patients with osteoarthritis at multiple sites.

SUBJECTS

White Dutch probands aged 40 to 70 years and their siblings with primary osteoarthritis at multiple sites.

METHODS

The diagnosis of knee, hip, and spine osteoarthritis was based on a combination of pain or stiffness on most days of the previous month and osteophytes or joint space narrowing on x ray. Hand osteoarthritis was defined by ACR criteria. Odds ratios (OR) were calculated for siblings and probands sharing disease in the same joints.

RESULTS

191 sibling pairs were included (85% women; mean age 60 years). In the probands, osteoarthritis was present in spine (76%), hands (77%), knees (37%), and hips (26%). The most common combinations in probands were spine-hand (59%), spine-knee (27%), and hand-knee (25%). The OR adjusted for age, sex, and body mass index for siblings to be affected in the same joint sites as the proband were increased in osteoarthritis of the hand (OR = 4.4 (95% confidence interval, 2.0 to 9.5)), hip (OR = 3.9 (1.8 to 8.4)), spine (OR = 2.2 (1.0 to 5.1)), hip-spine (OR = 4.7 (2.1 to 10.4)), and hand-hip (OR = 3.4 (1.1 to 10.4)). Siblings of probands with osteoarthritis in the knee did not have an increased likelihood of knee osteoarthritis.

CONCLUSIONS

In middle aged patients with familial osteoarthritis at multiple sites, familial aggregation of osteoarthritis was most striking for hand and hip but remarkably absent for the knee.

Genetic risk of knee osteoarthritis: a sibling study

OBJECTIVES

To determine whether there is a genetic contribution to knee osteoarthritis (OA) as defined by structural change on plain radiographs.

DESIGN

Sibling study. Comparison of knee OA prevalence in the community with knee OA prevalence among siblings of index cases with knee OA.

SUBJECTS

490 knee OA index cases listed for total knee replacement and 737 of their siblings aged >40 years, 1729 community subjects aged >40 years.

MAIN OUTCOME MEASURE

Odds ratio for radiographic knee OA in siblings v community participants.

RESULTS

The age, sex, and knee pain adjusted odds ratios in siblings were 2.9 (95% confidence interval 2.3 to 3.7) for tibiofemoral OA and 1.7 (1.4 to 2.2) for patellofemoral OA. This difference remained after adjustment for important environmental risk factors. The heritability estimate for knee OA was 0.62.

CONCLUSIONS

Siblings are at increased risk of knee OA in comparison with the general population. This is likely to be due to genetic factors.

Influence of radiographic phenotype on risk of hip osteoarthritis within families

OBJECTIVE

To determine whether the magnitude of the genetic influence on the development of hip osteoarthritis (OA) varies according to the radiographic phenotype within families.

PARTICIPANTS AND METHODS

331 families in which at least one sibling (index participant) had undergone total hip replacement for OA and whose preoperative x ray findings were available; 505 siblings of these index participants, who have high exposure to genetic risk of hip OA; and 1718 participants who had previously undergone intravenous urography, representative of the average general population exposure to genetic risk. Prevalence of hip OA was determined by individual radiographic features and minimum hip joint space. OA phenotype was partitioned according to pattern of femoral head migration and osteophyte bone response. Age adjusted odds ratios for hip OA in siblings, stratified according to phenotypic pattern in their index sibling, were assessed by unconditional logistic regression.

RESULTS

The superior pattern of femoral head migration was more common in men, and the axial pattern more common in women. A poor bone response (absent osteophytosis) was associated with an indeterminate pattern of migration. The age adjusted odds ratios for definite hip OA were twofold higher in siblings of index participants who had no osteophyte response than in siblings whose index case had any degree of osteophyte (OR 2.05, 95% CI 1.12 to 3.76). The risk of the siblings from these families having undergone hip replacement themselves was threefold higher. Patterns of migration and bone response were not concordant within families, even among same sex siblings.

CONCLUSION

Careful phenotypic characterisation is essential for genetic studies of hip OA. The results of these studies are likely to be influenced by the phenotypic pattern of hip disease, particularly osteophyte bone response.

Genetics of osteoarthritis

Osteoarthritis (OA) is a major cause of morbidity, physical limitation, and health care use, including total joint arthroplasty. That OA has a genetic component has been known for some time, but only recently has formal study of this occurred. Twin studies, segregation analyses, linkage analyses, and candidate gene association studies have generated important information about inheritance patterns and the location in the genome of potentially causative mutations. Results across studies are not always concordant, however; this is likely the result of variations in study populations, disease definitions, evaluation of control subjects, and statistical analysis. Although the genetics of OA is complex and not completely understood, there is cause for optimism as rapidly improving technologies make the quest for the genes responsible for OA increasingly within reach. Family history of OA and joint replacement for OA should be assessed in the context of other potentially modifiable risk factors to attempt to alter patient outcome.

Risk factors for osteoarthritis: genetics

Although the multifactorial nature of osteoarthritis (OA) is well recognized, genetic factors have been found to be strong determinants of the disease. Evidence of a genetic influence of OA comes from a number of sources, including epidemiological studies of family history and family clustering, twin studies, and exploration of rare genetic disorders. Classic twin studies have shown that the influence of genetic factors is between 39% and 65% in radiographic OA of the hand and knee in women, about 60% in OA of the hip, and about 70% in OA of the spine. Taken together, these estimates suggest a heritability of OA of 50% or more, indicating that half the variation in susceptibility to disease in the population is explained by genetic factors. Studies have implicated linkages to OA on chromosomes 2q, 9q, 11q, and 16p, among others. Genes implicated in association studies include VDR, AGC1, IGF-1, ER alpha, TGF beta, CRTM (cartilage matrix protein), CRTL (cartilage link protein), and collagen II, IX, and XI. Genes may operate differently in the two sexes, at different body sites, and on different disease features within body sites. OA is a complex disease, and understanding its complexity should help us find the genes and new pathways and drug targets.

The genetic contribution to muscle strength, knee pain, cartilage volume, bone size, and radiographic osteoarthritis: A sibpair study

OBJECTIVE

To estimate the heritability of muscle strength, knee pain, cartilage volume, bone size, and radiographic osteoarthritis (ROA), and to assess whether heritability of the knee structural components is independent of ROA.

METHODS

A sibpair design was utilized. Sagittal T1-weighted fat-suppressed magnetic resonance imaging (MRI) of the right knee was performed to determine cartilage volume and bone size. Standing semiflexed radiographs of the same knee were obtained to assess the presence of ROA. Knee pain was assessed by questionnaire and muscle strength by dynamometry. Heritability was estimated using the genetic analysis program SOLAR.

RESULTS

A total of 128 subjects (61 men, 67 women; mean age 45 years) from 51 families representing 115 sibpairs were studied. Lower limb muscle strength had high heritability (42%; P = 0.02), as did knee pain (44%; P = 0.07). Heritability estimates for cartilage volume were 65% for medial tibial cartilage, 77% for lateral tibial cartilage, and 84% for patellar cartilage, and heritability estimates for bone size were 85% for medial tibial bone area, 57% for lateral tibial bone area, and 70% for patella bone volume (all P < or = 0.004). For ROA, heritability was 61% for presence (with a large standard error) (P = 0.16) and 61% for severity (P = 0.02). The estimates for tibial bone areas were the only ones markedly reduced after adjustment for body size, while all estimates with the exception of knee pain were independent of ROA. Cartilage and, to a lesser extent, bone sites investigated by MRI were largely under independent genetic control, with a lesser shared genetic component.

CONCLUSION

With the exception of prevalent ROA, all knee modalities assessed had high heritability, most likely reflecting a strong genetic component. Cartilage volume, bone size, and muscle strength all have the potential to be studied in quantitative trait linkage analyses, but their exact relevance with regard to OA remains uncertain at this time.

Association study of candidate genes for the prevalence and progression of knee osteoarthritis

OBJECTIVE

Osteoarthritis (OA), characterized by late-onset degeneration of articular cartilage, is recognized to have a genetic component. We examined the role of 26 single-nucleotide polymorphisms (SNPs) from 24 candidate genes in OA susceptibility and progression.

METHODS

We compared human complementary DNA libraries from OA-affected and normal cartilage and synovium and selected 22 genes in addition to the estrogen receptor alpha and vitamin D receptor genes. Based on the availability of polymorphisms, we proceeded to test whether genetic variation at those genes affected susceptibility to or progression of radiographic knee OA over a 10-year period in 749 women (mean age 64 years) from the longitudinal Chingford Study.

RESULTS

After adjusting for age and body mass index, we observed significant associations at ADAM12, BMP2, CD36, COX2, and NCOR2 with 3 OA susceptibility traits (presence/absence of joint space narrowing [JSN], presence/absence of osteophytes, and Kellgren/Lawrence [K/L] score). For the OA progression traits (change over 10 years in the K/L score, osteophyte grade, and JSN grade), we found significant associations with ADAM12, CILP, OPG, and TNA. Overall, we observed 15 associations with nominal significance (P < 0.05) and, by permutation analysis, found that such a number would be observed by chance only 3.8% of the time. Although these tests require replication, the stronger genetic associations observed are unlikely to be attributable simply to multiple comparisons.

CONCLUSION

Our results suggest that OA severity and progression have a multigenic and feature-specific nature. These findings should encourage the development of genetic diagnostics for OA progression based on multiple SNPs and help unravel some of the complex disease mechanisms in OA.

Search for linkage between hand osteoarthritis and 11q 12-13 chromosomal segment

OBJECTIVE

The aims of the present study were: (1) to evaluate the extent and mode of inheritance of hand osteoarthritis by using a large sample of ethnically homogeneous pedigrees of Caucasian origin; (2) to examine whether the synthetic measure of osteoarthritis according to Kellgren and Lawrence (K-L) and the more specific measure, namely, the extent of osteophytes development, have a similar putative genetic determination and pattern of biological inheritance and (3) to test the hypothesis that hand osteoarthritis dependent phenotypes are linked to the 11q 12-13 chromosomal region.

METHODS

The population of the present study comprised 1190 Chuvashians (Russian Federation) belonging to 295 nuclear families. Segregation analysis was carried out on a total sample. Sub-sample of 571 individuals was used to conduct Transmission/disequilibrium test (TDT) and model-based linkage analysis.

RESULTS

Adjusted for age, sex and other covariates, both OA phenotypes showed significant familial aggregation. The model fitting analysis strongly supported the hypothesis of a major gene effect on study traits. The inferred major gene explained about 52% of the osteophyte score (OPS) and 49% of the K-L score variation adjusted for confounding variables. The series of model-based linkage analyses and TDTs provided inconclusive evidence on possible linkage of both phenotypes to the 11q 12-13 chromosomal region.

CONCLUSIONS

We support the hypothesis of a major gene effect in heritability of hand osteoarthritis in both phenotypes. Despite the fact that some DNA markers showed statistically significant association to studied primary phenotypes, we find only weak evidence of linkage disequilibrium between hand osteoarthritis and the proximal part of the 11q 12-13 chromosomal segment (D11S1983 for K-L score and D11S1313 for OPS). The subject, however, a merit requires further investigation.

Finer linkage mapping of primary hip osteoarthritis susceptibility on chromosome 11q in a cohort of affected female sibling pairs

OBJECTIVE

To finer linkage-map a primary osteoarthritis (OA) susceptibility locus as a prerequisite to linkage disequilibrium/association analysis.

METHODS

A 50-cM interval of chromosome 11q that we had previously identified as harboring susceptibility to hip OA in a female sibling-pair cohort was subjected to finer linkage mapping. Thirty-five microsatellite markers with a mean marker interval of 1.4 cM were genotyped in 146 families containing female sibling pairs who were concordant for hip OA, as ascertained by total hip replacement.

RESULTS

Two-point and multipoint linkage analysis revealed 2 distinct regions of linkage within the 50-cM interval. The first locus had a linkage interval of 11.9 cM and was centered at 81.5 cM from the 11p telomere, with a maximum multipoint logarithm of odds (LOD) score of 2.4. The second region had a linkage interval of 6.5 cM and was centered at 93.1 cM from the 11p telomere, with a maximum multipoint LOD score of 1.8.

CONCLUSION

Dense linkage mapping has highlighted the presence of 2 loci on chromosome 11q, each conferring susceptibility to hip OA. Both loci are sufficiently narrow for association analysis to be undertaken.

Association of the interleukin-1 gene cluster on chromosome 2q13 with knee osteoarthritis

OBJECTIVE

To investigate whether the interleukin-1 (IL-1) ligand gene cluster at 2q13 encodes for genetic susceptibility to primary osteoarthritis (OA).

METHODS

Seven single-nucleotide polymorphisms (SNPs) and a variable-number tandem repeat (VNTR) polymorphism from within the IL-1 ligand genes IL1A, IL1B, and IL1RN were genotyped in a cohort of 557 OA cases and 557 age-matched controls.

RESULTS

None of the variants demonstrated association in the unstratified data set. However, when cases were stratified according to sex and site of disease (hip or knee), 4 SNPs showed marginal evidence for association (P < 0.1) in knee cases (n = 136) and male knee cases (n = 58). For 2 of these SNPs, evidence for association was enhanced when probands from 60 knee-only affected sibling pair families were genotyped and combined with the original knee cases (P < or = 0.05). Further analysis revealed that the associated alleles at 2 of these SNPs were markers for the same haplotype, the frequency of which was significantly elevated when knee cases and knee probands were combined (P = 0.01, odds ratio [OR] 1.4) and when male knee cases and male knee probands were combined (P = 0.009, OR 1.7). Furthermore, linkage analysis of 2q revealed suggestive evidence for linkage to the IL-1 gene clusters in affected sibling pairs concordant for knee OA but no evidence for linkage in affected sibling pairs concordant for hip OA.

CONCLUSION

The IL-1 ligand cluster encodes for susceptibility to knee OA but not to hip OA, highlighting the genetic heterogeneity of this common, complex disease.

Genetics of menopause-associated diseases

Menopause is the permanent cessation of menstruation resulting from the loss of ovarian follicular activity. It is estimated that perhaps 50 million women worldwide will go into menopause annually. Atherosclerotic cardiovascular disease, osteoporotic fractures and Alzheimer's dementia are common chronic disorders after menopause, representing major health problems in most developed countries. Apart from being influenced by environmental factors, these chronic disorders recognize a strong genetic component, and there are now considerable clinic evidences that these disorders are related to low hormonal milieu of postmenopausal women. Here, we review up-to-date available data suggesting that genetic variation may contribute to higher susceptibility to four sporadic chronic syndromes such as osteoporosis (OP), osteoarthritis (OA), Alzheimer's disease (AD) and coronary artery disease (CAD). For these four syndromes candidate genes that today appear as major loci in genetic susceptibility encode for proteins specific of a given system, as the vitamin D receptor (VDR) gene for the skeleton and, therefore, OP or angiotensin converting enzyme (ACE) for the cardiovascular system and, therefore, CAD. The investigation of gene polymorphisms in various pathological conditions typical of postmenopause offer an explanation not only of their genetic inheritance but also of their co-segregation in given individuals. In this view, it may be possible to identify a common set of genes whose variants contribute to a common genetic background for these different disorders. Ideal candidates appear genes of the estrogen response cascade [i.e. estrogen receptor (ERs), enzymes involved in estrogen metabolism or co-activators and co-inhibitors]. All together this information may represent the basis both for future recognition of individuals at risk and for the pharmacogenetic driving of drug responsiveness.

A large Icelandic family with early osteoarthritis of the hip associated with a susceptibility locus on chromosome 16p

OBJECTIVE

To describe a large kinship with inherited hip osteoarthritis (OA) and its associated susceptibility locus.

METHODS

Four generations of a kinship with familial hip OA were identified and characterized by family history and by clinical, radiographic, and histopathologic examination. In the genome-wide search for a susceptibility locus, OA cases were defined as those who had undergone total hip replacement associated with a clinical and radiographic diagnosis of hip OA. A genome-wide scan was performed using a framework set of microsatellite markers with an average spacing of 10 cM.

RESULTS

The hip OA of this family was indistinguishable from that of idiopathic, nonfamilial hip OA. There was no apparent evidence of spondyloepiphyseal dysplasia or other dysplasias usually associated with mutations in collagen genes. The genome-wide scan revealed a locus on chromosome 16p between 28 cM and 47 cM from the telomere, and this locus met the criteria for suggestive linkage (multipoint allele-sharing logarithm of odds [LOD] score 2.58, P = 1.6 x 10(-4)). Two additional regions with LOD scores of >1.5 were obtained.

CONCLUSION

We have identified and described the largest kinship with familial hip OA reported to date. Evidence for linkage in this family suggests that a gene for susceptibility to hip OA exists on chromosome 16p. This represents an independent identification of a susceptibility locus previously reported for hip OA in this geographic region.

Primary osteoarthritis of the hip: etiology and epidemiology

Primary osteoarthritis (OA) of the hip has a distinct etiology and epidemiology compared with other types of arthropathy in the hip joint. Arthritis of the hip can be secondary to conditions such as osteonecrosis, trauma, sepsis, or rheumatoid arthritis. Certain conditions, such as congenital hip disease and slipped capital femoral epiphysis, involve predisposing anatomic abnormalities; in such cases, the term "secondary OA" is used. When either an anatomic abnormality cannot be determined or other specific causative entities are not identified, primary OA is the diagnosis of exclusion. The prevalence of hip OA is about 3% to 6% in the Caucasian population and has not changed in the past four decades. In contrast, studies in Asian, black, and East Indian populations indicate a very low prevalence of hip OA. Statistics on patients who underwent total hip replacement for primary OA in San Francisco and Hawaii demonstrate a virtual absence of the condition in Asians and low rates in the black and Hispanic populations. Family studies from Sweden, Britain, and the United States show increased rates of hip OA in first-degree relatives of the index patient when compared with the normal population. Occupations requiring heavy lifting, farming, and elite sports activity are associated with increased rates of hip OA. The low prevalence of hip OA in Asian and black populations in their native countries; the low incidence of total joint replacement for primary OA in Asian, black, and Hispanic populations in North America; and the familial association of hip OA in Caucasians all suggest that genetic factors may be involved in the occurrence of this disease.

Genetic epidemiology of primary osteoarthritis

Primary osteoarthritis (OA) is a late onset disease that fits most accurately into the oligogenic, multifactorial class of genetic diseases. Twin pair and family risk studies have highlighted a surprisingly large genetic component to OA and have prompted the search for predisposing genes. These searches have taken three forms: (1) parametric linkage analysis of rare families in which OA segregates as a Mendelian trait, (2) model-free linkage analysis of affected sibling pairs, and (3) association analysis of known candidate genes. Within the past year linkage analysis studies have highlighted that chromosomes 2, 4, 6, 7, 11, 16, and the X may each harbor an OA susceptibility gene. Chromosomes 2, 4, and 16 were identified in multiple genome scans and are therefore the most likely to encode susceptibility. Association analysis of candidates suggests that the syntenic genes for type II collagen and the vitamin D receptor (12q12--q13.1) may also encode for OA susceptibility.

Genetic markers of osteoarticular disorders: facts and hopes

Osteoarthritis and osteoporosis are the two most common age-related chronic disorders of articular joints and skeleton, representing a major public health problem in most developed countries. Apart from being influenced by environmental factors, both disorders have a strong genetic component, and there is now considerable evidence from large population studies that these two disorders are inversely related. Thus, an accurate analysis of the genetic component of one of these two multifactorial diseases may provide data of interest for the other. However, the existence of confounding factors must always be borne in mind in interpreting the genetic analysis. In addition, each patient must be given an accurate clinical evaluation, including family history, history of drug treatments, lifestyle, and environment, in order to reduce the background bias. Here, we review the impact of recent work in molecular genetics suggesting that powerful molecular biology techniques will soon make possible both a rapid accumulation of data on the genetics of both disorders and the development of novel diagnostic, prognostic, and therapeutic approaches.

The inheritance of hip osteoarthritis in Iceland

OBJECTIVE

To assess, in a population-wide study in Iceland, the genetic contribution to hip osteoarthritis (OA) leading to total hip replacement (THR).

METHODS

Information from 2 population-based databases in Iceland was combined: a national registry of all THRs performed between 1972 and 1996, and a genealogy database of all available Icelandic genealogy records for the last 11 centuries. A genetic contribution to THR for OA was assessed by 1) identifying familial clusters of OA patients with THR, 2) applying the minimum founder test (MFT) to estimate the minimum number of ancestors ("founders") that would account for the genealogy of all 2,713 patients with THR for OA, compared with the average number of founders for control lists, 3) calculating an average pairwise kinship coefficient (KC) for the patient list and control lists, and 4) estimating the relative risk (RR) for THR among relatives of OA patients who have undergone the procedure. One thousand matched control lists, each the same size as the patient list, were created using the genealogy database.

RESULTS

A large number of familial clusters of patients with THR for OA were identified. The MFT showed that OA patients descended from fewer founders than did subjects in the control groups (P < 0.001). The average pairwise KC among patients with OA was greater than in the control population (P < 0.001). The RR for THR among siblings of OA patients was 3.05 (95% confidence interval 2.52-3.10).

CONCLUSION

This population-based study shows that Icelandic patients with hip replacement for OA are significantly more related to each other than are matched controls drawn from the Icelandic population. These findings support a significant genetic contribution to a common form of OA and encourage the search for genes conferring an increased susceptibility to OA.

Assessment of a genetic contribution to osteoarthritis of the hip: sibling study

OBJECTIVES

To study the influence of genetics on the development of hip osteoarthritis as determined by structural change on plain radiographs.

DESIGN

Sibling study.

SETTING

Nottinghamshire, England.

PARTICIPANTS

392 index participants with hip osteoarthritis of sufficient severity to warrant total hip replacement, 604 siblings of the index participants, and 1718 participants who had undergone intravenous urography.

MAIN OUTCOME MEASURE

Odds ratios for hip osteoarthritis in siblings.

RESULTS

The age adjusted odds ratios in siblings were 4.9 (95% confidence interval, 3.9 to 6.4) for probable hip osteoarthritis and 6.4 (4.5 to 9.1) for definite hip osteoarthritis. These values were not significantly altered by adjusting for other risk factors.

CONCLUSION

Siblings have a high risk of hip osteoarthritis as shown by structural changes on plain radiographs. One explanation is that hip osteoarthritis is under strong genetic influence.

The genetic contribution to radiographic hip osteoarthritis in women: results of a classic twin study

OBJECTIVE

To assess the genetic contribution to radiographic hip osteoarthritis (OA) by measuring the distribution of disease features in monozygotic (MZ) and dizygotic (DZ) twins.

METHODS

A population-based, cross-sectional study was conducted of 135 MZ and 277 DZ healthy female twin pairs, 50 years of age and older, who were recruited into the St. Thomas' UK Adult Twin Registry. Pelvic radiographs were read by a single observer who was blinded to the pairing and zygosity of the twins. The films were assessed for overall OA grade using a modification of the Kellgren and Lawrence scheme, and assessed for individual radiographic features.

RESULTS

There was evidence of significant familial clustering for grade I and grade II OA changes, with an excess concordance in MZ twins compared with DZ twins, suggesting a genetic effect. The MZ versus DZ excess was also apparent for those classified as having more severe disease, although the number of pairs with these disease features was small. Familial clustering attributable to genetic factors was evident for joint space narrowing of <2.5 mm. Familial, but not genetic, clustering was seen for subchondral sclerosis. The number of pairs concordant for definite osteophytes in the sample was too low to assess this feature alone. These results translate into a significant heritability of 58% for OA overall and 64% for joint space narrowing. The heritability estimates decreased a little when the potential confounding influences of age, body mass index, and hip bone density were taken into account.

CONCLUSION

Genetic factors have a significant contribution to OA at the hip in women and account for approximately 60% of the variation in population liability to the disease.

Adjacent genes, for COL2A1 and the vitamin D receptor, are associated with separate features of radiographic osteoarthritis of the knee

OBJECTIVE

To study the association of the COL2A1 genotype, in relation to the vitamin D receptor (VDR) genotype, with features of radiographic osteoarthritis (ROA) in a population of elderly men and women.

METHODS

In this cross-sectional study, we analyzed a population-based sample of 851 men and women ages 55-80 years from a large cohort study, the Rotterdam Study. We determined the prevalence of ROA of the knee according to the Kellgren/Lawrence (K/L) score and features of ROA (presence of osteophytes and narrowing of the joint space [JSN]) without considering clinical parameters of the disease. Genotypes were determined at a variable-number tandem repeats marker 1 kb downstream of the COL2A1 gene using a newly developed heteroduplexing method. The VDR genotype was previously determined by a direct molecular haplotyping polymerase chain reaction method to establish the phase of alleles at 3 adjacent restriction fragment length polymorphisms for Bsm I, Apa I, and Taq I.

RESULTS

We found the COL2A1 genotype to be associated with a 2-fold increased risk for JSN, but not with osteophytes or the K/L score. We had previously found the VDR genotype to be associated with osteophytes and the K/L score, but not with JSN. When the COL2A1 genotype was analyzed in combination with the VDR genotype, we found evidence suggesting that the presence of haplotypes of the 2 genes was associated with increased risk for ROA.

CONCLUSION

Our findings demonstrate that both the COL2A1 gene and the VDR gene are involved in ROA, but in separate features. The COL2A1 genotype is associated with JSN, while the VDR genotype is associated with osteophytes.

What can we do about osteoarthritis?

Osteoarthritis is complex in genetics, pathogenesis, monitoring and treatment. Current treatment of osteoarthritis does not influence progression. Much could be gained by more effective 'low-tech-low-cost' treatment. However, many patients have rapidly progressive disease, multiple joint involvement, and severe disease. We need to clarify the genetics of osteoarthritis, identify those at risk for progression and severe disease, and identify molecular processes critical for joint survival and failure. Will saving the cartilage improve patient pain and function? Effective outcome measures are needed to accelerate testing of new treatments. Further improvement is needed in joint implant technology to decrease costs, wear and loosening.

Osteoarthritis-susceptibility locus on chromosome 11q, detected by linkage

We present a two-stage genomewide scan for osteoarthritis-susceptibility loci, using 481 families that each contain at least one affected sibling pair. The first stage, with 272 microsatellite markers and 297 families, involved a sparse map covering 23 chromosomes at intervals of approximately 15 cM. Sixteen markers that showed evidence of linkage at nominal P</=.05 were then taken through to the second stage, with an additional 184 families. This second stage confirmed evidence of linkage for markers on chromosome 11q. Additional markers from this region were then typed to create a denser map. We obtained a maximum single-point LOD score, at D11S901, of 2.40 (P=.0004) and a maximum multipoint-LOD score of 3.15, between markers D11S1358 and D11S35. A subset of 196 of the 481 families, comprising affected female sibling pairs, generated a corrected LOD score of 2.54 (P=.0003) for marker D11S901, with evidence for linkage extending 12 cM proximal to this marker. When we stratified for affected male sibling pairs there was no evidence of linkage to chromosome 11. Our data suggest that a female-specific susceptibility gene for idiopathic osteoarthritis is located on chromosome 11q.

Prevalence of hip osteoarthritis in Iceland

OBJECTIVE

To assess the prevalence of primary hip osteoarthritis (OA) in Iceland. To compare the prevalence of primary hip OA in Iceland with published rates of primary hip OA for related Scandinavian populations.

METHODS

Roentgenographs were examined of 1530 Icelandic people 35 years or older (653 males, 877 females) subjected to colon radiography during the years 1990-1996. The radiographs examined represent approximately 40% of all colon radiographs taken in Iceland during this period. After exclusion of non-primary hip OA cases, the minimum hip joint space was measured with a mm ruler. Presence of hip OA was defined as a minimum joint space of 2.5 mm or less on an anteroposterior radiograph. Intraclass correlation coefficients for inter and intraobserver variability of assessment of mm joint space were 0.91 and 0.95, respectively.

RESULTS

Of the 1517 people included, 227 hips in 165 patients (77 men, 88 women) were diagnosed as having radiological primary hip OA. The mean age at colon examination for these patients was 68 (35-89) years. The overall prevalence of coxarthrosis among all examined patients 35 years and older was 10.8% (12% for men, 10% for women), rising from 2% at 35-39 years to 35.4% for those 85 years or older. If the population structure (age and sex distribution) for those older than 35 years in Iceland was used to standardise prevalence for both Iceland and south Sweden (using previously published data for south Sweden), the age and sex standardised prevalence of hip OA for those older than 35 years in Iceland was 8%, compared with 1.2% for south Sweden.

CONCLUSIONS

The prevalence of radiological primary hip OA is very high in Iceland, and in excess of fivefold higher than the prevalence found by using similar techniques in studies on related populations in southern Scandinavia. The rate difference is particularly notable for those younger than 70 years.