Genetic epidemiology of osteoarthritis: Studies of familial aggregation and candidate genes

O steoalthritis eO A) is the most common rheumatic disease and an i.mportant cause of disability in the elderly (l,2). It is characterized by a progressive degeneration of articular cartilage of diarthrodial joint::; without synovial inflammation or bone erosions. Il leads in a minority of subjects to clinical OA, Le. joint pain, limited range of motion of the affected jOint, joint effusion, local inflanul1atory reaction or crepitus. The dinical diagnosis of OA is confirmed by radiographic evidence, reflecting deterioration of cal1ilage with narrowing of joint space, formation of osteophytes at the joint margins, development of sclerosis of subchondral bone and development of pseudocystic areas in subchondral bone. OA is a chronic disease with a multifactorial etiology that includes genetic factors (e.g. skeletal disorders, heritable forms of obesity\\ other systemic factors (e.g. age, sex, race, bone mineral density), biomechanical factors (e.g. trauma, joint deformity, muscle weakness) and environmental factors (e.g. nutrition, spons, estrogen replacement therapy). The genetic influence on the etiology of OA has long been recognized for women with Heberden's nodes and for patients with generalized OA 0,4). There is growing evidence from POFulationbased studies, that comnlOn forms of OA, such as hand and knee OA, are also heritable (5-7). Various mutations in several genes have been detected in families with severe early-onset OA associated with heritable disorders as osteochondrodysplasia, Stickler syndrome, chondrocalcinosis or epiphyseal dysplasia (8,9). It remains largely unclear which genes are involved in causing common forms of OA that occur in an elderly population. Finally, genetic susceptibility to OA could also result from genetic influences on risk factors for OA, like obesity and increased bone mineral density. This thesis first describes some issues of consideration when studying the genetic epidemiology of a complex disease as osteoarthritis (Chapter 2.1). Next, the methods of the studies presented in this thesis are described

Age affects joint space narrowing in patients with early active rheumatoid arthritis

Background: Joint space narrowing ( JSN) in rheumatoid arthritis (RA) may be a manifestation of (primary) osteoarthritis becoming more prominent with age. We investigated the severity and predictors of JSN progression among different age groups. Methods: 10-year follow-up data of the BeSt study, a randomised controlled treat-to-target trial in early RA were used. Annual X-rays of hands and feet were scored using the Sharp/van der Heijde score (SHS). Subgroups were defined by age at baseline: 55, 40<55 and <40 years. JSN progression predictors were assessed by Poisson regression. Results: Baseline JSN scores (median (IQR)) were igher in patients 55 (2.0 (0.0-6.0)) compared with the other age groups: 1.0 (0.0-3.0) 40<55 and 0.3 (0.0-3.0) <40, p<0.001. After 10 years, total JSN and SHS were similar in all age groups. In patients 55 the mean erythrocyte sedimentation rate (ESR) over time (relative risk 1.02 (95% CI 1.00 to 1.03)

Insulin-like growth factor I gene promoter polymorphism, collagen type II alpha1 (COL2A1) gene, and the prevalence of radiographic osteoarthritis: the Rotterdam Study

OBJECTIVE: To examine the role of an IGF-I gene promoter polymorphism in the prevalence of radiographic osteoarthritis (ROA), and study its interaction with the COL2A1 gene. METHODS: Individuals genotyped for IGF-I (n = 1546) and COL2A1 gene polymorphisms (n = 808) were selected from a random sample (n = 1583) derived from the Rotterdam study. The presence of ROA was defined as a Kellgren score of 2 or more in at least one of four joints (knee, hip, hand, and spine). Genotype specific odds ratios (OR) were adjusted for age, sex, body mass index, and bone mineral density using logistic regression. Interaction with the COL2A1 genotype was tested. RESULTS: Overall, no association was found between the IGF-I polymorphism and ROA. In subjects aged 65 years or younger (n = 971), the prevalence of ROA increased with the absence of the 192 base pair (bp) allele (p for trend = 0.03). Compared with homozygotes for the 192 bp allele, the prevalence of ROA was 1.4 times higher in heterozygotes (95% confidence interval, 1.0 to 1.8) and 1.9 times higher in non-carriers (1.1 to 3.3). There was evidence of interaction between the IGF-I and COL2A1 genes. Individuals with the risk genotype of both genes had an increased prevalence of ROA (OR 3.4 (1.1 to 10.7)). No effect was observed in subjects older than 65 years. CONCLUSIONS: SUBJECTS: with genetically determined low IGF-I expression (non-carriers of the 192 bp allele) may be at increased risk of ROA before the age of 65 years. Furthermore, an interaction between the IGF-I and COL2A1 genes is suggested

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 (CRTLl) genes. __Methods:__ Cases were selected from a populationbased 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 CRTLl 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

Heritabilities of radiologic OA in peripheral joins 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