Heritability of serum TSH, free T4 and free T3 concentrations: a study of a large UK twin cohort

OBJECTIVE

Thyroid hormone action influences many metabolic and synthetic processes, but the degree of regulation attributed to genes and environmental factors affecting normal variation remains controversial.

DESIGN

We investigated the magnitude of the genetic and environmental determination of serum concentrations of free (f) T3, fT4, TSH and the fT4 x TSH product and their variation, in a large cohort of twin pairs. Female dizygous and monozygous twins (849 and 213 pairs, respectively) from the TwinsUK registry (mean age 45.5, range 18-80 years) were studied.

RESULTS

Comparison of thyroid parameters within various groups showed no differences between smoking categories, and higher serum TSH and lower fT3 in subjects with positive thyroid antibodies. Using structural equation modelling, we estimated the heritable contribution to serum thyroid parameters (with 95% confidence intervals) to be 65% (58%-71%) for TSH, 65% (58%-71%) for the fT4 x TSH product, 39% (20%-55%) for fT4 and 23% (3%-41%) for fT3.

CONCLUSIONS

We conclude that genetic regulation is a particularly important determinant of TSH and the fT4 x TSH product, and is a less important determinant of fT4 and fT3 concentrations in Caucasian women. These data from a large well-characterized cohort suggest that while there is a strong heritable contribution to serum TSH, variation in fT4 and fT3 concentrations may be less explained by genetic factors and more driven by environmental effects than previously thought.

TUB is a candidate gene for late-onset obesity in women

AIMS/HYPOTHESES

We recently reported significant associations between BMI and three TUB single nucleotide polymorphisms (SNPs) in two Dutch cohorts enriched for type 2 diabetes. Here, we attempted a replication of these associations in a large population-based cohort of female twins comprehensively phenotyped for measures of general and central obesity.

METHODS

Two TUB SNPs (rs2272382, rs2272383) and a third (rs1528133), 22 kb distal to RIC3, were genotyped in 2694 Europid women from the St Thomas' UK Adult Twin Registry (Twins UK) (mean age +/- SD: 47.6 +/- 12.7 years; 42.8% postmenopausal). We explored the hypothesis that TUB is a candidate gene for late-onset obesity in humans through testing the interaction of the SNPs by menopausal status.

RESULTS

In the whole cohort, none of the three SNPs showed a significant main effect on measures of general or central obesity. However, for central obesity the rs2272382 SNP showed a significant interaction with menopausal status (p = 0.036). Postmenopausal women homozygous for the minor allele of rs2272382 showed significantly more general obesity (p = 0.022) and central obesity (p = 0.009) than carriers of the major allele. Differences (beta [95% CI]) between the two genotype groups were 0.92 kg/m2 (0.03-1.81) for BMI (p = 0.036), 2.73 cm (0.62-4.84) for waist circumference (p = 0.013) and 2.43% (0.27-4.60) for per cent central fat (p = 0.027). These associations were confirmed by a sibling transmission disequilibrium test for central obesity, waist circumference and per cent central fat.

CONCLUSIONS/INTERPRETATION

We have replicated associations of TUB SNP rs2272382 with measures of general and central obesity in normal postmenopausal women. These findings confirm TUB as a candidate gene for late-onset obesity in humans.

The additive effect of individual genes in predicting risk of knee osteoarthritis

OBJECTIVE

Genetic factors are important determinants of osteoarthritis (OA) but most individual genetic associations appear relatively modest. We aimed to answer whether carrying several genetic variants associated with knee OA could result in a greater risk of OA.

METHODS

Genotypes for 36 single nucleotide polymorphisms (SNPs) in 17 candidate genes previously associated with OA were analysed in 298 men and 305 women diagnosed with knee OA who met American College of Rheumatology (ACR) criteria, and in 297 male and 299 female age- and ethnicity-matched controls. The S-sum statistic method was used to select SNPs that contributed to knee OA, separately for men and women, and the coefficients from a logistic regression were used to add the genotypes in a new genetic risk variable.

RESULTS

The odds ratio for individuals in the top quartile of the "genetic risk" variable compared to those in the bottom quartile was found to be 8.68 (95% CI 5.20-14.49, p<2x10(-16)) for women and 5.06 (95% CI 3.10-8.27, p<1x10(-10)) for men.

CONCLUSIONS

Our data suggest that the additive information from a number of genetic variants can predict a substantial proportion of risk of knee OA.

Is telomere length in peripheral blood lymphocytes correlated with cancer susceptibility or radiosensitivity?

Mean terminal restriction fragment (TRF) lengths in white blood cells (WBCs) have been previously found to be associated with breast cancer. To assess whether this marker could be used as a test for breast cancer susceptibility in women, TRF length was measured in 72 treated female breast cancer patients and 1696 unaffected female controls between the ages of 45 and 77 from the Twin Research Unit at St Thomas' Hospital, as well as 140 newly diagnosed breast cancer cases and 108 mammographically screened unaffected controls from Guy's Hospital. Mean TRF was also tested for correlation with chromosome radiosensitivity and apoptotic response in the Guy's Hospital patients. After adjusting for age, smoking and body mass index, there was no significant difference in TRF lengths between the treated breast cancer patients and unaffected controls (P=0.71). A positive correlation between age-adjusted apoptotic response and mean TRF in newly diagnosed untreated breast cancer patients (P=0.008) was identified but no significant difference in TRF lengths between breast cancer patients and unaffected controls was detected (P=0.53). This suggests that TRF lengths in WBC, is not a marker of breast cancer susceptibility and does not vary significantly between affected women before and after treatment.

Effects of strontium ranelate on spinal osteoarthritis progression

OBJECTIVE

The aim of this study was to determine whether a 3-year treatment with strontium ranelate could delay the progression of spinal osteoarthritis (OA).

METHODS

This study was a post-hoc analysis of pooled data from the Spinal Osteoporosis Therapeutic Intervention (SOTI) and TReatment Of Peripheral OSteoporosis (TROPOS) trials performed on 1105 women with osteoporosis and concomitant radiological spinal OA at baseline, and for whom lumbar x-rays were available at baseline and over the 3-year treatment period. The presence and severity of osteophytes, disc space narrowing and sclerosis in the lumbar intervertebral spaces was graded according to a validated method, and an overall OA score was calculated for each intervertebral space. Back pain (measured on a five-point Likert scale only in SOTI) and health-related quality of life (SF-36 questionnaire) were assessed at baseline and after 3 years. Patients who suffered an incident or progressive vertebral fracture during the study were excluded from the analysis.

RESULTS

The proportion of patients with worsening overall spinal OA score was reduced by 42% in the strontium ranelate group, compared with placebo (RR, 0.58; 95% CI, 0.42 to 0.79; p = 0.0005). Significantly more patients in the strontium ranelate group experienced an improvement in back pain after 3 years, compared with placebo (p = 0.03), while no significant difference was observed in terms of health-related quality of life between these patient groups.

CONCLUSIONS

The results of this post-hoc analysis suggest that strontium ranelate could reduce the progression of the radiographic features of spinal OA and back pain in women with osteoporosis and prevalent spinal OA.

SHP-2 and PI3-kinase genes PTPN11 and PIK3R1 may influence serum apoB and LDL cholesterol levels in normal women

Insulin regulates apoB metabolism via activation of PI3K or regulation of MTP via MAPK/ERK signalling. SHP-2 enhances both pathways through increased IRS-1 phosphorylation. We hypothesized that variants in the SHP-2 gene PTPN11 and PI3K p85alpha subunit gene PIK3R1 may influence fasting levels of plasma apoB and/or LDL cholesterol. We tested association of tagging SNPs (tSNPs) in each gene with serum lipids in a large sample of unselected population-based Caucasian female twins (n=2771, mean age 47.4+/-12.5 years) and then tested interaction between tSNPs in determining apoB and LDL levels. PTPN11 tSNP rs11066322 was associated with apoB (P=0.007) and rs11066320 was associated with LDL cholesterol (P=0.016). PIK3R1 tSNP rs251406 was associated with apoB (P=0.0003) and rs706713 was associated with LDL cholesterol (P=0.009). PTPN11 tSNP rs11066322 interacted with PIK3R1 tSNP rs251406 in determining serum apoB levels (P=0.012) and with PIK3R1 tSNP rs40318 in determining LDL cholesterol levels (P=0.009). Association of single tSNPs with both apoB and LDL cholesterol as well as interactions between the two genes suggest that variants influencing SHP-2 activity may modulate the acute pathway by which insulin regulates these lipids.

Telomere length in leukocytes correlates with bone mineral density and is shorter in women with osteoporosis

Telomere length decreases with age and is associated with osteoblast senescence. In 2,150 unselected women, leukocyte telomere length was significantly correlated with bone mineral density. Clinical osteoporosis was associated with shorter telomeres, suggesting that telomere length can be used as a marker of bone aging.

INTRODUCTION

The length of telomeres in proliferative cells diminishes with age. Telomere shortening and telomerase activity have been linked to in vitro osteoblast senescence and to increased secretion of pro-inflammatory cytokines. We explored whether bone mineral density correlates with telomere length in leukocytes.

MATERIALS AND METHODS

The relationship between leukocyte telomere length, bone mineral density (BMD) and osteoporosis (as defined by the World Health Organization) was examined in a cohort of 2,150 women from a population-based twin cohort aged 18-79.

RESULTS

After adjusting for age, body mass index, menopausal status, smoking, hormone replacement therapy status, telomere length was positively correlated with BMD of the spine (p < 0.005), forearm (p < 0.013), but not the femoral neck (p < 0.06). Longer telomeres were associated with reduced the risk of clinical OP at two or more sites (odds ratio = 0.594 95% CI 0.42-0.84 p < 0.003) and in women over the age of 50, clinical osteoporosis was associated with 117 bp shorter telomere length (p < 0.02) equivalent to 5.2 years of telomeric aging.

CONCLUSIONS

Shortened leukocyte telomere length is independently associated with a decrease in BMD and the presence of osteoporosis in women. Our data provide evidence that leukocyte telomere length could be a marker of biological aging of bone.

The heritability of plasma homocysteine, and the influence of genetic variation in the homocysteine methylation pathway

BACKGROUND

The extent of genetic influence on plasma homocysteine, a risk factor for ischaemic heart disease, is uncertain. Many association studies have investigated common polymorphisms and their role in hyperhomocysteinaemia, but only the thermolabile variant of methylene tetrahydrofolate reductase (MTHFR) has shown an association (small but robust).

AIM

To estimate the heritability of plasma homocysteine and the contributions of well-studied common SNPs in the three main candidate genes in the homocysteine methylation pathway.

DESIGN

Twin study.

METHODS

We studied 216 monozygotic and 790 dizygotic pairs of twins; all were women. Blood was collected after overnight fasting for measurement of homocysteine, folate, vitamin B12, and extraction of DNA. Heritability was estimated by structural modelling, including correction for known environmental influences, particularly serum folate. The frequency of a common coding SNP in MTHFR and methionine synthase (MTR), and two coding SNPs in methionine synthase reductase (MTRR) were measured in dizygotic twins by ABI 7700 Sequence Detection, and the contribution of each to homocysteine variance was determined.

RESULTS

The heritability of homocysteine was 57% (95%CI 51-63%). The highest contribution to homocysteine was serum folate, accounting for 10.13% of variance. This was twice the total genetic contribution of 4.56%, and only the C1763T SNP of MTRR showed significant association with homocysteine.

DISCUSSION

Homocysteine has one of the highest heritabilities of common risk factors for ischaemic heart disease. This is not accounted for by the commonly studied SNPs in MTHFR, MTR and MTRR.

Lumbar disc disease shows linkage to chromosome 19 overlapping with a QTL for hand OA

OBJECTIVE

Cervical and lumbar degenerative disc disease (CDD and LDD, respectively) form part of the spine osteoarthritis (OA) phenotype and are known to be influenced by genetic factors. A genome-wide linkage analysis was performed to identify new chromosomal regions of interest.

METHODS

Dizygotic healthy female twin volunteers (n = 348) from the TwinsUK register who had magnetic resonance imaging scans 10 years ago coded for degenerative disease, were identified. Multipoint genome-wide linkage analysis was conducted using 737 highly polymorphic markers of approximate spacing 10 cM.

RESULTS

The mean age of the twins was 52 years. Significant linkage peaks (log of the odds (LOD) >3) were identified for LDD at three chromosomal regions. These included chromosome 1 (position 285 cM), chromosome 5 (position 175 cM) and chromosome 19 (position 80 cM). The peak on chromosome 19 had LOD = 4.06, and the empirical p = 6.7x10(-4) confirmed reliability of the linkage signal. It lies close to a linkage peak previously obtained by our group for hand OA.

CONCLUSIONS

This genome-wide linkage study of CDD and LDD shows evidence of linkage for LDD on chromosome 19. The region of interest is likely to harbour genes that are common to LDD and hand OA.

Polymorphisms in ALOX12, but not ALOX15, are significantly associated with BMD in postmenopausal women

The murine arachidonate 15-lipoxygenase gene (Alox15) has recently been identified as a negative regulator of peak bone mineral density (BMD). The human ALOX15 gene shares significant sequence homology with the murine Alox15 gene; however, the human arachidonate 12-lipoxygenase gene (ALOX12) is functionally more similar to the mouse gene. Multiple single-nucleotide polymorphisms (SNPs) in the human ALOX15 and ALOX12 genes have previously been reported to be significantly associated with BMD in humans. On the basis of these data, we carried out our own investigation of the human ALOX15 and ALOX12 genes and their relationship with hip and spine BMD parameters. The study population consisted of 779 postmenopausal women with a mean (+/- standard deviation) age of 62.5 +/- 5.9 years at BMD measurement and was recruited from a single large general practice in Chingford, northeast London. Three SNPs from ALOX15 and five from ALOX12 were analyzed. None of the SNPs that we analyzed in ALOX15 were significantly associated with any of the BMD parameters or fracture data. However, we found that three SNPs from ALOX12, all previously associated with spine BMD in women, were significantly associated with spine and various hip BMD parameters in our cohort (P = 0.029-0.049). In conclusion, we found no association between polymorphism in ALOX15 and BMD phenotypes but were able to replicate previous findings that genetic variation in ALOX12 seems to play a role in determining bone structure in Caucasian women.

Attitudes towards human reproductive cloning, assisted reproduction and gene selection: a survey of 4600 British twins

BACKGROUND

Surveys have shown opposition to human reproductive cloning (HRC) in many countries. Views of identical (monozygotic, MZ) twins are of particular interest, as they naturally share 100% of their genes. We investigated attitudes of British twins towards HRC in the context of assisted reproduction technologies (ART) and gene selection.

METHODS

About 4651 identical and non-identical (dizygotic, DZ) twins expressed their degree of agreement or disagreement to nine statements relating to ART, gene selection and HRC in a self-completion questionnaire.

RESULTS

Most subjects (70% and 78% respectively) did not regard the use of medical technologies to treat infertility as interfering with either nature or God's will, despite believing that infertility is not a disease (54%). Attitudes to gene selection and HRC were context dependent, with more favourable views towards preventing serious diseases than towards enhancing traits. About 44% supported a permanent ban of HRC. MZ twins were significantly more likely to agree that HRC should be allowed for medical purposes, such as saving a sibling's life, than were DZ twins. Increasing religiosity generally correlated with more negative attitudes.

CONCLUSIONS

Many attitudes are context dependent. More positive views of MZ twins towards HRC could be linked to their experience with being genetically identical.

Association between KLOTHO gene and hand osteoarthritis in a female Caucasian population

OBJECTIVE

Osteoarthritis (OA) is a common complex disease with strong heritable components. In this study, we investigated the association between four putatively functional genetic variants in KLOTHO gene, a strong ageing-related gene, and hand OA in a large female Caucasian population.

METHODS

Subjects (n=1015, age range 33-74 years) were selected from the TwinsUK Registry. Radiographs of both hands were taken for each individual with standard posteroanterior view. The presence/absence of radiographic OA, osteophyte and joint space narrowing (JSN) was assessed using a standard atlas. Four putatively functional single nucleotide polymorphisms (SNPs) in KLOTHO gene were genotyped using allelic discrimination assay. Association was initially estimated using Pearson's chi(2) or Fisher's exact test at allelic and genotypic levels. The direction and magnitude of significant association were further investigated by robust logistic regression with age as a covariate.

RESULTS

We found significant association between SNP G-395A and the presence/absence of radiographic hand OA and osteophyte, but not JSN. Allele G significantly increased the risk for radiographic hand OA and osteophytes with odds ratios (ORs) of 1.44 (P=0.008, 95% confidence interval (CI) 1.09-1.91) and 1.36 (P=0.006, 95% CI 1.09-1.70), respectively. From logistic regression modelling, genotype GG showed more than three-fold increased risk for both radiographic hand OA (OR=3.10, 95% CI 1.10-8.76) and osteophyte (OR=3.10, 95% CI 1.10-8.75) when compared to genotype AA. After adjustment for age, ORs for genotype GG further increased to 4.39 (P=0.006, 95% CI 1.51-12.74) for radiographic hand OA and to 4.47 (P=0.005, 95% CI 1.56-12.77) for osteophytes.

CONCLUSIONS

Our results suggest that one variant in KLOTHO gene is associated with the susceptibility of hand OA and appears to act through osteophyte formation rather than cartilage damage.

Serum adiponectin and bone mineral density in women

CONTEXT

Bone mineral density (BMD) is positively associated with body weight. This association persists even at non-load bearing sites, suggesting that a nonmechanical factor such as an adipocyte-derived hormone may modulate BMD.

OBJECTIVE

The objective of the study was to evaluate the relationship between adiponectin, an adipocyte-derived hormone, and BMD.

DESIGN, SETTING, PARTICIPANTS

A total of 1735 nondiabetic women were recruited from a large, population-based cohort (mean age, 50.0 yr). We employed linear regression methods to estimate the relationship between adiponectin and BMD.

MAIN OUTCOME MEASURES

Percentage change in BMD (as measured at total hip, spine, femoral neck, and forearm) and markers of bone turnover associated with a doubling of fasting serum adiponectin levels were measured.

RESULTS

Employing age-adjusted analysis, each doubling of serum adiponectin was associated with a mean 2.7% decrease in BMD [total hip, -3.2% (95% confidence interval, -4.1, -2.3); femoral neck, -3.1% (-4.0, -2.1); forearm, -2.0 (-2.6, -1.4); spine, -2.6 (-3.5, -1.7)]. After adjustment for potential confounding factors, including BMI, serum leptin, central fat mass, hormone replacement therapy, smoking, and exercise, this relationship persisted, although decreased in magnitude. When stratified by menopausal status, the relationship between serum adiponectin and BMD strengthened in postmenopausal women but disappeared in premenopausal women. Serum adiponectin was positively associated with serum osteocalcin but not with urine deoxypyridinoline.

CONCLUSIONS

After adjustment of measures of body fat, increasing levels of adiponectin were associated with a decrease in BMD, even at non-load bearing sites. These data suggest that adiponectin, an adipocyte-derived hormone, may play a role in bone metabolism through nonmechanical mechanisms and that this effect may be mediated by menopausal status.

An analysis of which anti-osteoporosis therapeutic regimen would improve compliance in a population of elderly adults

OBJECTIVE

Although medications to prevent osteoporotic fractures have been proven to be effective, compliance to these therapies is generally poor. Therapeutic regimens for different anti-osteoporotic medications differ widely and it is currently unknown which regimen would be most preferred by patients.

RESEARCH DESIGN AND METHODS

We conducted a large, population-based study to discern which therapeutic attributes would be most preferable to a population representative of the age and sex distribution of patients with osteoporosis.

RESULTS

Our study sample was restricted to persons aged 55 years and over and comprised 2485 individuals (mean age of 64.5 years). The study population was predominantly female (90.3%) and two-thirds of the respondents reported current daily medication use. Nearly half (45%) of the study population preferred to take medications daily, while one in five preferred weekly therapy and 30% preferred monthly therapy (p < 0.0001 for between proportion comparisons). When given the option of choosing between three different medication regimen scenarios, those subjects not currently using anti-osteoporotic medications preferred a theoretical regimen which was daily and did not involve subsequent fasting and maintaining an upright posture.

CONCLUSIONS

Our data suggest that compliance with osteoporotic medications could be improved if patients are able to choose a therapeutic regimen best suited to their particular needs. The majority of subjects preferred a drug which was taken daily and with minimal inconvenience, rather than a weekly drug with slightly more inconvenience. Given that most physicians currently prescribe anti-osteoporotic therapy as a weekly regimen, at the time of diagnosis physicians should ascertain which regimen would be most preferable to patients prior to initiating therapy.

Genetic influence on the progression of radiographic knee osteoarthritis: a longitudinal twin study

OBJECTIVE

Genetic influences on rates of osteoarthritis (OA) progression are unknown. Our aim was to estimate the heritability of progression of radiographic knee OA using a longitudinal twin study.

METHODS

Unselected monozygotic (MZ) and dizygotic (DZ) twin pairs from the TwinsUK registry were utilized. Anteroposterior radiographs were performed on both knees at baseline and follow-up using the same protocol. Radiographic features of knee OA including osteophyte and joint space narrowing (JSN) were assessed on a four-point scale using a standard atlas. Progression of knee osteophyte and JSN was defined as the difference in the corresponding score between follow-up and baseline > or =1. Liability threshold modelling using logistic regression was utilized for heritability estimation.

RESULTS

A total of 114 MZ pairs and 195 DZ pairs were studied. The average follow-up time was 7.2 years. Medial progression of osteophyte and JSN was more common than lateral progression. Prevalence of progression was generally higher in the MZs than the DZs. Similarly, concordances and tetrachoric correlations for both osteophyte and JSN were higher in the MZs than the DZs although only significant for overall and medial JSN and osteophyte. The heritability estimates were 69% [95% confidence interval (CI) 42-97%] and 80% (95% CI 50-100%) for medial osteophyte and JSN, respectively. The estimates were reduced by 7-15% after adjustment for age, body mass index (BMI), and the severity of osteophyte/JSN at baseline.

CONCLUSION

Our data documented a substantial genetic influence on the progression of knee OA--as seen in the medial compartment, providing a solid basis to search for genes involved in this highly relevant clinical trait.

Schmorl's nodes: Common, highly heritable, and related to lumbar disc disease

OBJECTIVE

Schmorl's nodes (SN) are common, but little is known of their relationship with degenerative change and back pain or genetic and environmental factors influencing their expression. We studied healthy female twin volunteers to determine the prevalence and clinical features associated with SN.

METHODS

Serial sagittal T1- and T2-weighted magnetic resonance images of the lower thoracic and lumbar spine were analyzed in 516 healthy female twins (150 monozygotic and 366 dizygotic). The images were scored for lumbar degenerative change. Presence of SN was noted at cranial and caudal vertebral levels T9 to L5. Data on physical activity and back pain were collected by questionnaire. Heritability of SN was calculated using variance components modeling.

RESULTS

SN were found in 30% of subjects. Of the 374 SN, 153 (41%) were in the lumbar spine and 221 (59%) were in the thoracic spine. SN heritability was >70%. There was a positive association between SN and lumbar disc disease (LDD). SN were more frequent in subjects with back pain (for >/=2 SN: odds ratio [OR] 2.68, 95% confidence interval [95% CI] 1.11-6.47, P = 0.03), but this was largely accounted for by the association of SN with LDD (OR 1.97, 95% CI 0.78-5.0, P = 0.15 adjusted for LDD). No independent association of SN with back pain was identified.

CONCLUSION

SN are common in middle-aged women and are strongly genetically determined. They are associated with lumbar degenerative change, which is a risk factor for back pain, but are not themselves an independent risk factor for back pain.

Prevalence of premature ovarian failure in monozygotic and dizygotic twins

BACKGROUND

Premature ovarian failure (POF) before 40 years of age from natural causes affects approximately 1% of adult women, with minor variations between ethnic groups. A recent case of ovarian transplantation between young monozygotic (MZ) twins in which one had undergone unexplained POF at 14 years has prompted a study of the prevalence of POF.

METHODS

Menopausal ages of 832 Australian and UK female twin-pairs were extracted from volunteer national twin registry databases containing medical, reproductive and lifestyle data surveyed by mail questionnaire. Surgical menopause was an exclusion criterion.

RESULTS

The prevalence of POF in both MZ and dizygotic (DZ) twins was similar in both registries and 3- to 5-fold greater than the general population at age thresholds 40 and 45 years. No specific factors were found to account for the higher risk of early menopause. Some twins of both zygosities were highly discordant for menopausal age (>or=10 years). Nevertheless, there was significant intra-twin dependence, especially for MZ twins, and the average age difference at last menses was greater in DZ twin-pairs.

CONCLUSION

Both MZ and DZ twins are at higher risk of POF. Despite some striking differences within MZ twin-pairs, menopausal ages were more concordant than for DZ twin-pairs, confirming that the timing of menopause has a heritable component.

Reduction of leucocyte telomere length in radiographic hand osteoarthritis: a population-based study

BACKGROUND

Although age is the strongest predictor of osteoarthritis, the exact mechanism underlying this disorder remains elusive.

OBJECTIVE

To examine the association between leucocyte telomere length (LTL), a bio-indicator of ageing, and radiographic hand osteoarthritis.

METHODS

An unselected, predominantly female sample from the TwinsUK Adult Twin Registry (Twin Research and Genetic Epidemiology Unit, St Thomas Hospital, London, UK) was studied. Radiographs of both hands were obtained with a standard posteroanterior view and assessed for radiographic osteoarthritis according to the Kellgren/Lawrence (K/L) score. Individual radiographic features including osteophytes and joint space narrowing (JSN) were also assessed on a four-point scale using a standard atlas. Hand osteoarthritis was defined radiographically as having >or=3 osteoarthritis-affected joints of both hands (K/L score>or=2). Severity of hand osteoarthritis was indicated semiquantitatively by total K/L scores, osteophytes, JSN scores and proportion of joints affected. Mean LTL was measured by the terminal restriction fragment length using the Southern blot.

RESULTS

A total of 1086 Caucasian subjects (mean (SD) age 55 (8.0) years) were studied. LTL was 6.95 (0.64) kb and was inversely correlated with age. After adjustment for age, sex, body mass index and smoking, LTL was significantly shorter by 178 bp in subjects with hand osteoarthritis (n = 160) than in those without (n = 926; p = 0.04). LTL was also significantly associated with semicontinuous measures of osteoarthritis (eg, total K/L score, JSN score, osteophyte score and proportion of joints affected) after adjustment (all p<or=0.02) in a dose-response fashion.

CONCLUSION

Shorter LTL equivalent to around 11 years of annual loss in normal people is associated with radiographic hand osteoarthritis and disease severity, suggesting potential shared mechanisms between osteoarthritis and ageing, and implicating oxidative stress and low-level chronic inflammation in both conditions.

The effects of social status on biological aging as measured by white-blood-cell telomere length

Low socio-economic status (SES) is associated with a shortened life expectancy, but its effect on aging is unknown. The rate of white-blood-cell (WBC) telomere attrition may be a biological indicator of human aging. We tested the hypothesis that SES is associated with telomere attrition independent of known risk factors influencing the aging process. We studied 1552 female twins. A venous blood sample was taken from each twin and isolated WBCs used for extraction of DNA. Terminal restriction fragment length (TRFL) was measured. Questionnaire data were collected on occupation, education, income, smoking, exercise, height and weight. Standard multiple linear regression and multivariate analyses of variance tested for associations between SES and TRFL, adjusting for covariates. A discordant twin analysis was conducted on a subset to verify findings. WBC telomere length was highly variable but significantly shorter in lower SES groups. The mean difference in TRFL between nonmanual and manual SES groups was 163.2 base pairs (bp) of which 22.9 bp (approximately 14%) was accounted for by body mass index, smoking and exercise. Comparison of TRFL in the 17 most discordant SES twin pairs confirmed this difference. Low SES, in addition to the harmful effects of smoking, obesity and lack of exercise, appears to have an impact on telomere length.

The big finger: the second to fourth digit ratio is a predictor of sporting ability in women

BACKGROUND

The second to fourth finger length ratio (2d:4d) is thought to be related to diverse traits including cognitive ability, disease susceptibility, and sexuality.

OBJECTIVE

To examine the relationship between 2d:4d and sports ability in women.

METHODS

Hand radiographs from 607 women (mean age 54 years) were used to estimate 2d:4d. Ranking of sports ability was on a scale (1-5).

RESULTS

The highest achieved level of participation in any sport was significantly negatively associated with 2d:4d (b = -4.93, p = 0.01) as was the relationship between 2d:4d and running level (b = -6.81, p = 0.034). Ability in other sports also showed a negative relationship albeit non-significant.

CONCLUSIONS

These results suggest that a low 2d:4d ratio is related to increased female sports ability. It can be postulated that this ratio may predict potential sports ability. Understanding the mechanisms underpinning this relationship may give important insights into musculoskeletal fitness, health and disease.

Heritability of DNA-damage-induced apoptosis and its relationship with age in lymphocytes from female twins

Apoptosis is a physiological form of cell death important in normal processes such as morphogenesis and the functioning of the immune system. In addition, defects in the apoptotic process play a major role in a number of important areas of disease, such as autoimmune diseases and cancer. DNA-damage-induced apoptosis plays a vital role in the maintenance of genomic stability by the removal of damaged cells. Previous studies of the apoptotic response (AR) to radiation-induced DNA damage of lymphoid cells from individuals carrying germline TP53 mutations have demonstrated a defective AR compared with normal controls. We have also previously demonstrated that AR is reduced as individuals age. Results from the current study on 108 twins aged 18–80 years confirm these earlier findings that the AR of lymphoid cells to DNA damage is significantly reduced with increasing age. In addition this twin study shows, for the first time, that DNA-damage-induced AR has a strong degree of heritability of 81% (95% confidence interval 67–89%). The vital role of DNA-damage-induced apoptosis in maintaining genetic stability, its relationship with age and its strong heritability underline the importance of this area of biology and suggest areas for further study.

AMP-kinase alpha2 subunit gene PRKAA2 variants are associated with total cholesterol, low-density lipoprotein-cholesterol and high-density lipoprotein-cholesterol in normal women

BACKGROUND

5'-AMP-activated protein kinase (AMPK) inactivates critial ensymes in fatty acid and cholesterol synthesis. We hypothesised that the serum lipid profile may be influenced by genetic variation in the AMPK catalytic alpha2 subunit.

METHOD

We examined association of 5 tagging SNPs (tSNPs) in the PRKAA2 gene with serum lipids in 2777 normal Caucasian females (mean age 47.4+/-12.5 years).

RESULTS

All tSNPs were associated with total- and LDL-cholesterol, (p<0.001 to 0.034), explaining variances of 0.13-0.59% and 0.11-0.55% respectively. One haplotype (frequency 34.7%) showed lower total- and LDL-cholesterol compared with the most common haplotype (frequency 45.7%) (p< or =0.001), explaining 0.78% of total- and 0.75% of LDL-cholesterol. Another haplotype (frequency 10.5%) was significantly associated with lower HDL-cholesterol (p = 0.005), explaining 0.59% of variance.

CONCLUSIONS

PRKAA2 gene variants are significantly associated with serum lipoproteins in a large sample of normal female Caucasians.

The relation between progressive osteoarthritis of the knee and long term progression of osteoarthritis of the hand, hip, and lumbar spine

BACKGROUND

The association between progression of knee osteoarthritis and progression of osteoarthritis at sites distant from the knee is unclear because of a lack of multisite longitudinal progression data.

OBJECTIVE

To examine the association between radiological progression of knee osteoarthritis and osteoarthritis of the hands, hips, and lumbar spine in a population based cohort.

METHODS

914 women had knee x rays taken 10 years apart, which were read for the presence of osteophytes and joint space narrowing (JSN). Progression status was available for hand, hip, and lumbar spine x rays over the same 8 to 10 year period. The association between progression of knee osteoarthritis and osteoarthritis at other sites was analysed using odds ratios (OR) and 95% confidence intervals (CI) in logistic regression models.

RESULTS

89 of 133 women had progression of knee osteoarthritis based on osteophytes, and 51 of 148 based on JSN definition. Progression of JSN in the knee was predicted by progression in lumbar spine disc space narrowing (OR = 2.9 (95% CI 1.2 to 7.5)) and hip JSN (OR = 2.0 (1.0 to 4.2)). No consistent effects were seen for hand osteoarthritis. The associations remained after adjustment for age and body mass index.

CONCLUSIONS

Progression of knee osteoarthritis is associated with progression of lumbar spine and hip osteoarthritis. This may have implications for trial methodology, the selection of patients for osteoarthritis research, and advice for patients on prognosis of osteoarthritis.