Genetic influences on osteoarthritis in women: a twin study

Heritabilities of radiologic osteoarthritis in peripheral joints and of disc degeneration of the spine

OBJECTIVE

To estimate the genetic influence on the occurrence of radiologic osteoarthritis (ROA) in the knees, hips, and hands and disc degeneration of the spine in the general population.

METHODS

A random sample of 1,583 individuals was drawn to estimate the prevalence of ROA and disc degeneration in the general population. Of 118 probands with multiple affected joint sites who were derived from this sample, we were able to recruit 257 siblings. The variance of ROA and disc degeneration within sibling pairs was compared with the variance between sibling pairs. Heritability estimates for ROA in the knees, hips, and hands and for disc degeneration of the spine were calculated. OA was defined according to radiologic criteria, using the Kellgren/Lawrence grading system.

RESULTS

We observed that hand ROA and disc degeneration of the spine were statistically significantly more frequent in siblings than in the random sample, whereas the prevalence of knee and of hip ROA was similar and lower, respectively. Heritability estimates for hand ROA and disc degeneration were statistically significant, P = 0.56 (95% confidence interval [95% CI] 0.34-0.76) and P = 0.75 (95% CI 0.30-1.00), respectively. For knee and hip ROA, no evidence of a genetic effect in the general population was found. Finally, the heritability estimate for a score that summed the number of joints affected in the knees, hips, hands, and spine was 0.78 (95% CI 0.52-0.98). All heritability estimates were adjusted for age, sex, body mass index, and bone mineral density.

CONCLUSION

The present study shows that in the general population, there is a strong genetic effect for hand ROA and disc degeneration of the spine. The findings on the total number of joints affected at multiple sites suggest genetic susceptibility to generalized OA.

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.

Molecular markers of bone and cartilage metabolism

Molecular markers of bone and cartilage metabolism are increasingly used as helpful tools in the diagnosis and early detection of joint disease. Their quantification may help to improve the ability for therapeutic monitoring and follow-up of patients affected with rheumatic or degenerative cartilage disorders. The biochemical background and the functional properties of markers of bone, cartilage, and synovial tissue turnover are described. Current clinical applications and the diagnostic and prognostic validity of these metabolites are presented with special emphasis on recent research activities. Finally, molecular aspects of bone and joint diseases are discussed, highlighting genetic contributions to the development of joint disease.

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.

Genetic influences on cervical and lumbar disc degeneration: a magnetic resonance imaging study in twins

OBJECTIVE

Degenerative intervertebral disc disease is common; however, the importance of genetic factors is unknown. This study sought to determine the extent of genetic influences on disc degeneration by classic twin study methods using magnetic resonance imaging (MRI).

METHODS

We compared MRI features of degenerative disc disease in the cervical and lumbar spine of 172 monozygotic and 154 dizygotic twins (mean age 51.7 and 54.4, respectively) who were unselected for back pain or disc disease. An overall score for disc degeneration was calculated as the sum of the grades for disc height, bulge, osteophytosis, and signal intensity at each level. A "severe disease" score (excluding minor grades) and an "extent of disease" score (number of levels affected) were also calculated.

RESULTS

For the overall score, heritability was 74% (95% confidence interval [95% CI] 64-81%) at the lumbar spine and 73% (95% CI 64-80%) at the cervical spine. For "severe disease," heritability was 64% and 79% at the lumbar and cervical spine, respectively, and for "extent of disease," heritability was 63% and 63%, respectively. These results were adjusted for age, weight, height, smoking, occupational manual work, and exercise. Examination of individual features revealed that disc height and bulge were highly heritable at both sites, and osteophytes were heritable in the lumbar spine.

CONCLUSION

These results suggest an important genetic influence on variation in intervertebral disc degeneration. However, variation in disc signal is largely influenced by environmental factors shared by twins. The use of MRI scans to determine the phenotype in family and population studies should allow a better understanding of disease mechanisms and the identification of the genes involved.

Incidence and risk factors for radiographic knee osteoarthritis in middle-aged women: the Chingford Study

OBJECTIVE

To examine the natural history, role of risk factors, and incidence of knee osteoarthritis (OA) in a prospective study of women from a population cohort.

METHODS

Women from the Chingford Study who had been recruited in 1989 were followed up with knee radiographs 4 years later. A total of 715 paired radiographs (71% of the original sample) were graded for osteophytes and 644 for joint space narrowing (JSN). Women whose radiographs had been graded as 0 in 1989 and as > or =14 years later were classified as having incident disease. Incident cases were compared with controls for associations with a number of risk factors.

RESULTS

Eighty-one women (12.6%) developed JSN of the knee, equating to an incidence of 3.1% per year. No clear risk factors for JSN were identified. Reproducibility of measures of joint space is poor, however, leading to inaccuracy of definition. Incident knee osteophytes developed in 95 women (133%), equating to an incidence of 3.3% per year. Compared with controls, women with incident knee osteophytes were older, heavier, and had more hand OA and knee symptoms. Women in the top tertile of obesity (body mass index >26.4) had a significantly increased risk of incident knee osteophytes (odds ratio [OR] 2.38, 95% confidence interval [95% CI] 1.29-4.39). Incident knee osteophytes increased by 20% per 5-year age increase. A nonsignificant protective effect for incident knee osteophytes was seen with current estrogen replacement therapy (ERT) (OR 0.41, 95% CI 0.12-1.42). No effect was associated with smoking, physical activity, hysterectomy, or previous knee injury.

CONCLUSION

Obesity and aging are associated with a high risk of new knee OA developing in women. Evidence of a protective effect of ERT was seen. No clear association was found for incident JSN, suggesting that different etiologic mechanisms are operating or that standard radiographs are an inaccurate measure of incident narrowing.

Grip strength and the risk of developing radiographic hand osteoarthritis: results from the Framingham Study

OBJECTIVE

In knees, quadriceps strength may protect against osteoarthritis (OA). Muscle activity is a major determinant of forces at the hand joints, and grip is a common task during which high muscle forces are sustained, especially at the proximal hand joints (metacarpophalangeal [MCP] joints and thumb base). This longitudinal study of radiographic hand OA examined the association between incident OA at different hand joints and maximal grip strength.

METHODS

Four hand joint groups were studied: distal interphalangeal (DIP), proximal interphalangeal (PIP), MCP, and the base of the thumb (carpometacarpal and scaphotrapezial combined). Subjects were members of the Framingham OA Study who had a baseline radiograph in 1967-1969 and a followup radiograph in 1992-1993 (mean followup 24 years) and had no prevalent radiographic OA in any hand joint at baseline. Incident disease was defined as development of OA defined as a modified Kellgren/Lawrence grade of > or =2. Grip strength was measured in kilograms by dynamometer in 1958-1961 and again in 1960-1963, and the 2 measures were averaged and divided into sex-specific tertiles. Joint-based analysis was performed by adjusting for age, physical activity, and occupational category using the lowest grip strength tertile as the referent.

RESULTS

Baseline and followup radiographs were obtained from 746 subjects. Of these, 453 subjects with no prevalent OA at baseline were eligible for analysis. In men, higher maximal grip strength was associated with an increased risk of OA in the PIP (highest tertile odds ratio [OR] 2.8 compared with lowest tertile, 95% confidence interval [95% CI] 1.2-6.7), MCP (highest tertile OR 2.9, 95% CI 1.1-7.4), and thumb base joints (highest tertile OR 2.8, 95% CI 1.1-7.4). In women, there was increased risk of OA in the MCP joints (highest tertile OR 2.7, 95% CI 1.1-6.4).

CONCLUSION

Men with high maximal grip strength are at increased risk for the development of OA in the PIP, MCP, and thumb base joints, and women, in the MCP joints. No association was found between maximal grip strength and incident OA in the DIP joints of men or women.

Evidence for genetic anticipation in nodal osteoarthritis

OBJECTIVE

Evidence was sought for genetic anticipation (disease occurring at an earlier age in subsequent generations, with increasing severity) in nodal osteoarthritis (NOA).

METHODS

Age at symptom onset and disease severity was compared within 30 parent/offspring pairs with NOA. Correlation between the offspring age of disease onset and the parental age at conception was also assessed.

RESULTS

The age at onset of nodal symptoms was earlier in the offspring (43 years (95% confidence intervals (CI) 38 to 47) v 61 (CI 58 to 65); mean difference 18 years (CI 13 to 22): p < 0.001) as was larger joint symptom onset (48 years (CI 41 to 55) v 67 (CI 61 to 73); mean difference 20 years (CI 13 to 27): p < 0.01). A negative correlation existed between age of offspring symptom onset and parental age at conception. Fifteen (50%) offspring had similar or more extensive disease than their parents.

CONCLUSIONS

These results suggest genetic anticipation occurs in NOA and if confirmed a search for trinucleotide repeats is warranted.

Familial aggregation of osteoarthritis: data from the Baltimore Longitudinal Study on Aging

OBJECTIVE

To evaluate the familial aggregation of osteoarthritis (OA) in a cohort of healthy volunteers drawn from a community setting.

METHODS

Hand radiographs obtained between 1978 and 1991 and bilateral standing knee radiographs obtained between 1984 and 1991 were read for changes of OA, using Kellgren-Lawrence (K-L) scales. The hand sites were distal interphalangeal (DIP) joints, proximal interphalangeal (PIP) joints, and first carpometacarpal (CMC1) joints. For each joint group, the presence of OA in at least 1 joint in a joint group, the number of affected digits in each joint group, and the sum of the K-L grade across all joints were analyzed. Polyarticular OA was recorded if there were OA findings in 2 of 3 hand joint groups plus 1 or both knees. Data from 167 families with hand radiographs, 157 families with knee radiographs, and 148 families with both hand and knee radiographs were analyzed for sib-sib correlations.

RESULTS

After adjustment for age, sex, and body mass index, clinically relevant sib-sib common correlations were found for OA of the DIP, PIP, and CMC1 joints, for OA at 2 or 3 hand sites, and for polyarticular OA (r = 0.33-0.81) when OA was defined according to the number of affected joints or as the sum of the K-L grade across all joints.

CONCLUSION

These results from a cohort of volunteers drawn from a community setting and ascertained without regard to OA status demonstrate familial aggregation of OA and contribute to the evidence for heritability of OA.

Evidence for a Mendelian gene in a segregation analysis of generalized radiographic osteoarthritis: the Framingham Study

OBJECTIVE

To investigate the inheritance of generalized osteoarthritis (OA).

METHODS

OA was identified on hand and knee radiographs obtained from members of the Framingham Study cohort (the parents) in 1967-1970 and 1992-1993, and from their adult children in the Framingham Offspring Study in 1993-1994. All hand and knee radiographs evaluated for OA were graded using the Kellgren and Lawrence (K/L) scale. A measure of generalized OA was defined as the count of the number of hand and knee joints affected, as determined by the proportion of joints with a K/L grade > or =2. The OA count, treated as a continuous variable, was adjusted for age, body mass index, and a measure of physical activity for each joint area (hand or knee). Calculations were made separately for each generation and each sex, and correlations were analyzed against the standardized residual of OA. Segregation analysis was used to test whether OA aggregated in families, and if its transmission fit a Mendelian pattern.

RESULTS

A total of 337 nuclear families with 2 parents and at least 1 biologic offspring were studied. In parents, the mean age was 61.2 years at the time of hand radiographs and 72.8 years at the time of knee radiographs, which were mostly obtained at a later examination. The mean age at the time of radiographs in offspring was 53.9 years. Using standardized residuals, parent-offspring and sibling-sibling correlations ranged from 0.115 to 0.306. In segregation analyses, models testing the hypotheses of no familial aggregation, no familial transmission, or a Mendelian gene alone were all rejected (P < 0.001 for each of these models). The best-fitting models were mixed models with a Mendelian mode of inheritance and a residual multifactorial component. The Mendelian recessive model provided the best fit.

CONCLUSION

These analyses support a significant genetic contribution to OA, with evidence for a major recessive gene and a multifactorial component, representing either polygenic or environmental factors.

Allelic variation in the vitamin D receptor, lifestyle factors and lumbar spinal degenerative disease

OBJECTIVE

To describe the relation between spinal degenerative disease, allelic variation in the vitamin D receptor gene, and lifestyle factors in a population-based association study.

METHODS

Random population-based sample of 110 men and 172 women over 60 years of age participating in the Dubbo Osteoporosis Epidemiology Study who had spinal radiographs (performed according to a standardised approach), assessment of lifestyle factors, bone densitometry as well as blood taken for genotyping.

RESULTS

Spinal degenerative disease of varying severity was common in this sample. Multivariate analysis of genetic and lifestyle factors simultaneously strengthened the statistical significance of each indicating the presence of additive gene environment interaction. Allelic variation in the vitamin D receptor gene was associated with severity of osteophytosis (adjusted OR "TT" v "tt" 0.41, 95% CI 0.17, 0.97), presence of disc narrowing (adjusted OR "TT" v "tt" 0.45, 95% CI 0.20, 0.99) and weakly with presence of osteophytosis (adjusted OR "TT" v "tt" 0.47, 95% CI 0.19, 1.16) but not with severity of disc narrowing (OR "TT" v "tt" 1.05, 95% CI 0.40, 2.72) or apophyseal arthritis (OR "TT" v "tt" 0.63, 95% CI 0.24, 1.59). Adjustment for femoral neck bone density did not change these findings suggesting that the association is not mediated through bone density. Presence and severity of spinal degenerative disease increased with age at all sites. Current smoking increased both the presence (adjusted OR 9.70, 95% CI 2.08, 45.1) and severity (adjusted OR 2.91, 95% CI 1.16, 9.03) of spinal osteophytosis with intermediate values for past smokers. Severity of osteophytosis was also independently associated with body mass index and quadriceps strength consistent with a contributory effect of physical loading.

CONCLUSIONS

In this elderly sample, both genetic and lifestyle factors were associated with the presence and severity of spinal degenerative disease. There were site specific differences in associations at the spine, which may be because of misclassification of disease status or may indicate possible environmental and genetic differences in the pathophysiology of spinal degenerative disease. Further studies are required to confirm these findings in different population samples and to further explore potential aetiological mechanisms particularly gene environment interaction.

What is the relationship between osteoarthritis and osteoporosis?

Several epidemiological studies have shown a lower incidence and prevalence of hip fractures in people with osteoarthritis (OA) and vice versa which has led to numerous studies examining the association between OA and osteoporosis more generally. There is felt to be an inverse relationship between these two diseases and the evidence for and against this association is discussed. The evidence for an association with osteoporosis is stronger for large joint OA than hand OA or primary generalized OA. A number of possible mechanisms for this association are discussed such as genetic factors, common risk factors, role of subchondral bone in cartilage damage and growth factors. The incidence and prevalence of one disease in the presence of the other is discussed. Despite the inverse relationship seen in some studies, there is currently no evidence that treatment of one disease can have a detrimental effect on the other.

What is the evidence that osteoarthritis is genetically determined?

Although for many years it was speculated that osteoarthritis was genetically determined, little data were available to support this contention. A major problem with early work was a lack of consistency in the definition of osteoarthritis. Based on a radiographical definition of osteoarthritis, which is currently the optimal method for epidemiological and genetic studies, data from a recent twin study have provided an estimate of the hereditable component of osteoarthritis to be in the order of 50 to 65%. In addition, sophisticated molecular biology techniques are being increasingly used to explore potential genetic abnormalities in cartilage and matrix components in osteoarthritis. These exciting new data are examined as we address the role of genetic factors in osteoarthritis.

Investigation of the association of the CRTM and CRTL1 genes with radiographically evident osteoarthritis in subjects from the Rotterdam study

OBJECTIVE

To investigate whether radiographically evident osteoarthritis (ROA) in 55-65-year-old men and women is associated with specific alleles or genotypes of the cartilage matrix protein (CRTM) and cartilage link protein (CRTL1) genes.

METHODS

Cases were selected from a population-based study on the presence of ROA of the knee or hip. Further radiographic analysis included scoring for spine and hand ROA. Controls, selected from the same population, were free of ROA in all joints.

RESULTS

The CRTM locus was significantly associated with hip ROA in men (odds ratio 0.50, 95% confidence interval 0.26-0.95). A significant association between ROA and the CRTL1 gene was not observed.

CONCLUSION

These results suggest that the CRTM locus may play a role in the sex- and joint site-specific pattern of ROA development.

Association of early osteoarthritis of the knee with a Taq I polymorphism of the vitamin D receptor gene

OBJECTIVE

To determine whether a polymorphism of the vitamin D receptor (VDR) gene, already associated with osteoporosis, might also relate to the risk of osteoarthritis (OA).

METHODS

A population cohort of 351 postmenopausal women (ages 45-64 years) was studied using anteroposterior radiographs of the knee, which were graded for OA according to the Kellgren and Lawrence classification system. The VDR genotype was determined by using polymerase chain reaction and by digestion with the restriction enzyme Taq I.

RESULTS

The VDR allele "T" was associated with an increased risk of knee OA compared with the "t" allele, with an odds ratio of 2.82 (95% confidence interval 1.16-6.85; P = 0.02). A dominant pattern of risk was suggested. The frequency of the VDR genotype differed significantly between OA cases and controls (P = 0.03 by Fisher's exact test).

CONCLUSION

A Taq I polymorphism of the VDR gene appears to be associated with an increased risk of knee OA. This is the first genetic locus that has been shown to influence the risk of early knee OA within the general population.

Vitamin D receptor genotype is associated with radiographic osteoarthritis at the knee

Osteoporosis and osteoarthritis are age-related disorders of the skeleton with genetic components. Low bone density is a risk factor for osteoporotic fracture while osteoarthritis is associated with increased bone density. The 1,25-dihydroxyvitamin D3 receptor (VDR) gene locus was previously found to be associated with bone density. We therefore studied the relationship between radiographic osteoarthritis at the knee and VDR genotype in a population-based sample (n = 846), using molecular haplotyping of anonymous intragenic DNA polymorphisms. Radiographic osteoarthritis was defined using the Kellgren score, which is based on the assessment of osteophytes and joint space narrowing (JSN). We show that one VDR haplotype allele is significantly overrepresented in individuals with knee osteoarthritis and associated with a 2.27-fold increased relative risk (95% confidence interval 1.46, 3.52). Adjustment for bone density at the femoral neck did not change these results, indicating that the association is not mediated by bone density. The association appeared to be largely explained by the presence of osteophytes rather than JSN. Our results indicate a role of the VDR gene in the pathogenesis of osteophytes while linkage disequilibrium with another nearby gene, i.e., the collagen type IIa1 gene encoding the most abundant protein in cartilage, might contribute to the association.

Genetic and environmental components of the population variance in bone density

Understanding of the genetic and environmental factors contributing to the differences in fracture rates between young and old, between women and men, and between races is limited. The reasons for this may partly relate to the lack of a detailed understanding of the structural basis of bone fragility. This information, although difficult to obtain because of the invasiveness of bone biopsy, will be required if advances are to occur. aBMD cannot be relied upon as an endpoint in the study of the pathophysiology of osteoporosis. Advances will require the description of the age-, gender and race-specific means and variances in trabecular number, thickness, spacing and orientation, cortical thickness, and bone size and shape in women and men of different racial groups. Subsequent comparison of the structures in young versus old, female versus male, and in racial groups may reveal the structural differences from which inferences may be made concerning the differences in fracture rates between these groups. By defining the structural basis for bone fragility, the genetic and modifiable environmental determinants of these structures may then be identified, providing hypotheses to be tested in randomized trials aimed at reducing the incidence of fractures in these groups.