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Biomedical subjects

Kirsten Ohm Kyvik

Publications and source records attributed to Kirsten Ohm Kyvik.

At least 19 recordsLinked to original sources
PubMed2006

Genetic and environmental interrelations between measurements of thyroid function in a healthy Danish twin population.

Serum thyrotropin (TSH), free thyroxine (T4), and free triiodothyronine (T3) levels illustrate the thyroid function set point, but the interrelations between these have never been characterized in detail. The aim of this study was to examine the associations between TSH and thyroid hormone levels in healthy euthyroid twins and to determine the extent to which the same genes influence more than one of these biochemical traits; 1,380 healthy euthyroid Danish twins (284 monozygotic, 286 dizygotic, 120 opposite-sex twin pairs) were recruited. Genetic and environmental associations between thyroid function measurements were examined using quantitative genetic modeling. In bivariate genetic models, the phenotypic relation between two measurements was divided into genetic and environmental correlations. Free T4 and free T3 levels were positively correlated (r=0.32, P<0.0001). The genetic correlation between serum free T4 and free T3 levels was rg=0.25 (95% CI 0.14-0.35), suggesting that a set of common genes affect both phenotypes (pleiotropy). The correlation between the environmental effects was re=0.41 (0.32-0.50). From this we calculated that the proportion of the correlation between free T4 and free T3 levels mediated by common genetic factors was 48%. Only 7% of the genetic component of serum free T3 levels is shared with serum free T4. Serum TSH and thyroid hormone levels did not share any genetic influences. In conclusion, thyroid hormone levels are partly genetically correlated genes that affect free T4 levels and exert pleiotropic effects on free T3 levels, although most of the genetic variance for these measurements is trait specific.

Adult↗
PubMed2006

Quality of life in unaffected twins discordant for affective disorder.

BACKGROUND: The disability and hardship associated with affective disorder is shared by the family members of affective patients and might affect the family member's quality of life. METHOD: In a cross-sectional, high-risk, case-control study, monozygotic (MZ) and dizygotic (DZ) twins with (High-Risk twins) and without (the control group/Low-Risk twins) a co-twin history of affective disorder were identified through nationwide registers. The aim of the present study was to investigate the hypothesis that a genetic liability to affective disorder is associated with a lower perception of quality of life. RESULTS: Univariate analyses showed that quality of life in all domains was impaired for the 121 High-Risk twins compared to the 84 Low-Risk twins. In multiple regression analyses, the differences remained significant after adjustment for sex, age, marital status and years of education. Adjusted for the effect of subclinical anxiety and depressive symptoms, the differences were significant on the domain environment and total WHOQoL-BREF and marginally significant on the domain physical health and overall quality of life. LIMITATIONS: It is not possible from the cross-sectional analyses to distinguish between subsyndromal state and trait scores. CONCLUSIONS: Perceived health related quality of life might share common familial vulnerability with affective disorders. Having a co-twin with affective disorder seem to have a negative influence on quality of life of the healthy co-twin and this influence might be due to the genetic liability to affective disorder. These findings need to be replicated in future family studies.

Adult↗
PubMed2006

Low birth weight is not associated with thyroid autoimmunity: a population-based twin study.

CONTEXT: Low birth weight has been proposed as a risk factor for the development of antibodies toward thyroid peroxidase (TPOAb) and thyroglobulin (TgAb) in adult life. However, the association could also be due to genetic or environmental factors affecting both birth weight and the development of thyroid autoantibodies. The effect of these confounders can be minimized through investigation of twin pairs. OBJECTIVE AND DESIGN: To examine the impact of low birth weight on the development of thyroid autoimmunity, we studied whether within-twin-cohort and within-twin-pair differences in birth weight are associated with differences in the serum concentration of TPOAb and TgAb in adult life. PARTICIPANTS: We studied 1024 euthyroid twin individuals who were distributed in 512 same-sex twin pairs. METHODS: Original midwife protocols were traced manually through the Provincial Archives of Denmark. TPOAb and TgAb were measured using solid-phase time-resolved fluoroimmunometric assays. RESULTS: There were no statistically significant associations between birth weight and serum concentrations of TPOAb [regression coefficient (beta) = 0.003 (95% confidence interval, -0.010 to 0.015); P = 0.67] or TgAb [beta = 0.002 (-0.010 to 0.014); P = 0.77]. When restricting the analysis to twin pairs with a within-pair difference in birth weight of 500 g or greater or to twin pairs born 4 wk or more before term, the regression coefficients were almost unchanged. Controlling for potential confounders (sex, zygosity, gestational age, TSH, and smoking) did not change the findings of nonsignificant regression coefficients. CONCLUSION: Low birth weight per se has no evident role in the etiology of thyroid autoimmunity.

Adult↗
PubMed2006

Cognitive function in unaffected twins discordant for affective disorder.

BACKGROUND: Patients may present with cognitive impairment in the euthymic phase of affective disorder, but it is unclear whether the impairment is prevalent before onset of the illness. The aim of the present study was to examine the hypothesis that genetic liability to affective disorder is associated with cognitive impairment. METHOD: In a cross-sectional high-risk case-control study, healthy monozygotic (MZ) and dizygotic (DZ) twins with (High-Risk twins) and without (the control group/Low-Risk twins) a co-twin history of affective disorder were identified through nationwide registers. Cognitive performance of 203 High-Risk and Low-Risk twins was compared. RESULTS: Healthy twins discordant for unipolar disorder showed lower performance on almost all measures of cognitive function: selective and sustained attention, executive function, language processing and working and declarative memory, and also after adjustment for demographic variables, subclinical symptoms and minor psychopathology. Healthy twins discordant for bipolar disorder showed lower performance on tests measuring episodic and working memory, also after adjustment for the above-mentioned covariables. The discrete cognitive impairment found seemed to be related to genetic liability, as the MZ High-Risk twins showed significant impairment on selective and sustained attention, executive function, language processing and working and declarative memory, whereas the DZ High-Risk twins presented with significantly lower scores only on language processing and episodic memory. CONCLUSIONS: The hypothesis that discrete cognitive impairment is present before the onset of the affective disorder and is genetically transmitted was supported. Thus, cognitive function may be a candidate endophenotype for affective disorders.

Adult↗
PubMed2006

Data collection on multiple births -- establishing twin registers and determining zygosity.

Twins are a valuable resource not only for studies on multiple births themselves, but on the etiology of diseases and other phenotypes. The method of ascertainment and selection of twins can be crucial for such studies and population based twin registries are thus of great importance as tools of research. Accurate determination of zygosity and chorionicity is essential in all studies of multiple births and in their professional care. The parents and the multiples ask for it. It is of pre-and postnatal medical importance and now considered as a prerequisite in several domains of twin research. It is also important for educational reasons as it helps the multiples and their parents and teachers to ascertain identity. The methods are briefly described and a plea is made to the obstetricians and pediatricians to use them systematically at birth. The distribution of zygosity and chorionicity types among spontaneous and induced twin births are illustrated.

Data Collection↗
PubMed2006

Genetic and environmental contributions to hay fever among young adult twins.

BACKGROUND: The susceptibility to develop hay fever is putatively the result both of genetic and environmental causes. We estimated the significance and magnitude of genetic and environmental contributions to hay fever among young adult twins. METHODS: From the birth cohorts 1953-82 of The Danish Twin Registry 11,750 twin pairs were identified through a nationwide questionnaire survey. Subjects were regarded hay fever cases when responding affirmatively to the question 'Do you have, or have you ever had hay fever?' Latent factor models of genetic and environmental effects were fitted to the observed data using maximum likelihood methods. RESULTS: The overall cumulative prevalence of hay fever was 12.6%. Identical twins were significantly more likely to be concordant for hay fever than were fraternal twins (P<0.001). Additive genetic effects accounted for 71% and non-shared environmental effects accounted for 29% of the individual susceptibility to hay fever. The same genes contributed to the susceptibility to hay fever both in males and in females. In families with asthma, the susceptibility to develop hay fever was, in addition to genes, to a great extent ascribable to family environment, whereas the aetiology of 'sporadic' hay fever was mainly genetic. CONCLUSIONS: The susceptibility to develop hay fever is attributable to major genetic influences. However, effects of family environment and upbringing are also of importance in families where asthma is present. These results indicate that different sub-forms of hay fever may have different aetiologies.

Adolescent↗
PubMed2006

Subclinical psychopathology and socio-economic status in unaffected twins discordant for affective disorder.

BACKGROUND: The most potent risk factor for affective disorders is a family history of affective disorder but the specific factors that are transmitted in families are unknown. It is possible to investigate the relation between risk factors and affective disorder by using a high-risk design e.g.: a study of the healthy relatives of patients with affective disorders. AIM: To compare psychopathology and socio-economic status between twins with a co-twin history of affective disorder and twins without. METHODS: In a cross-sectional high-risk case-control study, healthy monozygotic and dizygotic twins with (High-Risk twins) and without (Low-Risk twins) a co-twin history of affective disorder were identified through nation-wide registers. Participants were assessed using semi-structured psychiatric interviews and self-rating of psychopathology. RESULTS: High-Risk twins had a lower education level, a lower work position and tendency towards being more often unemployed and early retired than the Low-Risk twins. Furthermore, they presented higher rates of subclinical affective symptoms and were more likely to experience a minor psychiatric diagnosis. CONCLUSION: Healthy twins with a high genetic liability to affective disorder seem to present lower socio-economic status, higher rates of subclinical affective symptoms and more often experience a minor psychiatric diagnosis than twins with no familial history of affective disorder. It is not possible from the present cross-sectional data to determine the causality of these findings, thus genetic liability to affective disorder, socio-economic status and minor psychopathology seem to have a complex interrelation.

Adult↗
PubMed2006

Are lifestyle-factors in adolescence predictors for adult low back pain? A cross-sectional and prospective study of young twins.

INTRODUCTION: With more than half of the population experiencing low back pain (LBP) before the age of 20, research must focus on young populations. Lifestyle-factors might be important elements of prevention, since they are modifiable in nature. Therefore, the objective of the present study is to investigate the association between smoking, alcohol consumption and overweight in adolescence and 1) present LBP (cross-sectionally) and 2) the risk of future LBP (longitudinally). METHODS: Data from 9,600 twins, aged 12-22, were analysed cross-sectionally with respect to associations between the above-mentioned lifestyle-factors and LBP. Eight years later, a follow-up survey (n = 6,554) was conducted and LBP at follow-up was correlated to the lifestyle-factors at baseline. Finally, the associations found to be significant were tested in a twin-control study design. RESULTS: Our cross-sectional study demonstrated small, but statistically significant, positive associations between all three investigated life-style factors and LBP. In the longitudinal study, smoking at baseline showed a monotonic dose-response relationship with LBP at follow-up (OR up to 4.0 for those smoking >20 cig./day). There was also evidence of temporality (smoking preceding LBP). Adult LBP was negatively associated with adolescent alcohol consumption. We found no evidence of a dose-response relationship or temporality. There were no associations detected between adolescent overweight and adult LBP. In the twin-control study, the directions of associations were the same, but none of these associations attained statistical significance. CONCLUSION: Several of the Bradford Hill criteria for causality were fulfilled for smoking whereas the crucial aspect of temporality was missing for alcohol consumption and overweight. The twin-control study failed to confirm a statistically significant link between smoking and LBP.

Adolescent↗
PubMed2006

The course of low back pain from adolescence to adulthood: eight-year follow-up of 9600 twins.

STUDY DESIGN: Prospective study with 8-year follow-up. OBJECTIVE: To describe the evolution of low back pain from adolescence into adulthood. SUMMARY OF BACKGROUND DATA: High prevalence rates of low back pain among children and adolescents have been demonstrated in several studies, and it has been theorized that low back pain in childhood may have important consequences for future low back pain. It is important to understand the nature of such a link if effective preventive programs are to be established. METHODS: Almost 10,000 Danish twins born between 1972 and 1982 were surveyed by means of postal questionnaires in 1994 and again in 2002. The questionnaires dealt with various aspects of general health, including the prevalence of low back pain, classified according to number of days affected (0, 1-7, 8-30, >30). RESULTS: Low back pain in adolescence was found to be a significant risk factor for low back pain in adulthood with odds ratios as high as four. We also demonstrated a dose-response association: the more days with low back pain at baseline, the higher the risk of future low back pain. Twenty-six percent of those with low back pain for more than 30 days during the baseline year also had more than 30 days with low back pain during the follow-up year. This was true for only 9% of the rest of the sample. CONCLUSIONS: Our study clearly demonstrates correlations between low back pain in childhood/adolescence and low back pain in adulthood. This should lead to a change in focus from the adult to the young population in relation to research, prevention, and treatment.

Adolescent↗
PubMed2006

The Funen Neck and Chest Pain study: analysing non-response bias by using national vital statistic data.

OBJECTIVE: To describe the Funen Neck and Chest Pain (FNCP) study and carry out a comprehensive non-response analysis of the quality of the survey. METHODS: The FNCP questionnaire was sent out to 7000 randomly selected individuals aged 20-71 years living in Funen County, Denmark. A full description of the FNCP survey, analysis of selection bias (representativeness of the background population), selective bias (non-responder bias), and item non-response bias was performed by using Danish vital statistics. RESULTS: The adjusted response rate was 60%. Men, retired individuals, and individuals with lower income tended to be late responders. Women, people aged 50+, married individuals, and individuals with two or three children, with a higher educational level, living in a single house or with a high income were more likely to participate. Conversely, men, younger individuals, singles or divorced persons, individuals living in residential caring homes, and with lower educational level were less likely to participate. Adjustments based on design and logical omissions gave an overall missing data rate of 1.0%. In general, the frequency of missing data increased with age and was higher for women. The frequency of inconsistent answers was 0.34%. CONCLUSIONS: A comprehensive non-response analysis showed some sociodemographic discrepancies between the FNCP study and the background population. The pattern of missing data was strongly associated with the design of the questionnaire and with participants' willingness to answer only questions they considered relevant. These factors must be taken into consideration when results from the FNCP study are presented.

Adult↗
PubMed2006

Sex differences in heritability of neck pain.

Experimental studies have suggested biological factors as a possible explanation for gender disparities in perception of pain. Recently, heritability of liability to neck pain (NP) has been found to be statistically significantly larger in women compared to men. However, no studies have been conducted to determine whether the sex differences in heritability of NP are due to sex-specific genetic factors. Data on lifetime prevalence of NP from a population-based cross-sectional survey of 33,794 Danish twins were collected and age-stratified univariate biometrical modeling using sex-limitation models was performed based on 10,605 dizygotic (DZ) twins of opposite sex to estimate the qualitative sex differences. In a full sex-limitation model the genetic component in females were higher than in males, but the genetic and the shared environmental correlations were equal to what is normally assumed between same-sex DZ twins. A 'no-sex-effects' model showed the overall best model fit which confirms absence of sex-related gene interaction. The age-stratified sex-limitation models showed similar results. Thus, there is no evidence for a sex-specific genetic influence in the liability of heritability of NP.

Adult↗
PubMed2006

Prevalence, concordance, and heritability of Scheuermann kyphosis based on a study of twins.

BACKGROUND: The purpose of this study was to establish a cohort of symptomatic twins with Scheuermann kyphosis to provide estimates of prevalence, concordance, odds ratio, and heritability. These estimates indicate to what extent genetic factors contribute to the etiology of this disease. METHODS: The Odense-based Danish Twin Registry is unique in that it contains data on all 73,000 twin pairs born in Denmark over the last 130 years. For the present study, all 46,418 twins born from 1931 through 1982 received a seventeen-page questionnaire, in which one question was "Have you been diagnosed with Scheuermann disease by a doctor"? The prevalence of self-reported Scheuermann disease was calculated, with the total number of answers used as the general population. Pairwise and probandwise concordance, odds ratio, tetrachoric correlations, and heritability were calculated. RESULTS: We found that the overall prevalence of Scheuermann disease was 2.8%, with a prevalence of 2.1% among women and 3.6% among men (p < 0.0001). The pairwise concordance for monozygotic twins was 0.19 compared with 0.07 for dizygotic twins. The probandwise concordance was 0.31 for monozygotic twins and 0.13 for dizygotic twins. The odds ratios were 32.92 and 6.25 in the monozygotic and dizygotic twins, respectively. These differences were significant (p < 0.01). Heritability was 74%. CONCLUSIONS: In a large cohort of twins that included almost 35,000 individuals, the self-reported overall prevalence of Scheuermann disease was 2.8% and the male-to-female ratio was close to 2:1. Because the pairwise and probandwise concordance and the odds ratio were two to three times higher in monozygotic than in dizygotic twins and the heritability was high, we concluded that there is a major genetic contribution to the etiology of Scheuermann disease.

Adult↗
PubMed2005

High frequency of skewed X-chromosome inactivation in females with autoimmune thyroid disease: a possible explanation for the female predisposition to thyroid autoimmunity.

CONTEXT: Autoimmune thyroid diseases (AITD) comprise Graves' disease (GD) and Hashimoto's thyroiditis (HT). They are characterized by loss of immunological self-tolerance and female preponderance. Theoretically, X chromosome inactivation (XCI) and resultant tissue chimerism could offer an explanation for the female predisposition to AITD. AIM: Our aim was to examine whether skewed XCI is associated with AITD. DESIGNS: We first conducted a classical case-control study of twin individuals with and without AITD, and then a case-control study of twin pairs discordant for AITD. PARTICIPANTS: Participants included 32 female twins with AITD and a control group of 96 healthy female twin individuals. METHODS: XCI analysis was performed by enzymatic predigestion of DNA with a methylation-sensitive enzyme followed by PCR of the polymorphic CAG repeat of the androgen receptor gene. The XCI pattern was classified as skewed when 80% or more of the cells preferentially inactivated the same X chromosome. MAIN OUTCOME MEASURES: We assessed the prevalence of skewed XCI. RESULTS: The frequency of skewed XCI in female twins with AITD, GD, and HT was 34, 37, and 31%, respectively, which was higher than the prevalence in the corresponding control populations, 11% (P = 0.003), 14% (P = 0.045), and 8% (P = 0.057), respectively. Similar results were found in twin pairs discordant for AITD. Overall, skewed XCI was associated with an increased risk of developing AITD, with an odds ratio of 9.0 (95% confidence interval, 1.64-49.4) (P = 0.022). CONCLUSION: These observations suggest a possible role of XCI in the etiology of AITD and may in part explain the female preponderance of AITD.

Adult↗
PubMed2005

The prevalence of neck pain in the world population: a systematic critical review of the literature.

The objective of this study was to determine the prevalence of neck pain (NP) in the world population and to identify areas of methodological variation between studies. A systematic search was conducted in five databases (MEDLINE, EMBASE, CINAHL, OSH-ROM, and PsycINFO), followed by a screening of reference lists of relevant papers. Included papers were extracted for information and each paper was given a quality score. Mean prevalence estimates were calculated for six prevalence periods (point, week, month, 6 months, year, and lifetime), and considered separately for age, gender, quality score, response rate, sample size, anatomical definition, geography, and publication year. Fifty-six papers were included. The six most commonly reported types of prevalence were point, week, month, 6 months, year, and lifetime. Except for lifetime prevalence, women reported more NP than men. For 1-year prevalence, Scandinavian countries reported more NP than the rest of Europe and Asia. Prevalence estimates were not affected by age, quality score, sample size, response rate, and different anatomical definitions of NP. NP is a common symptom in the population. As expected, the prevalence increases with longer prevalence periods and generally women have more NP than men. At least for 1-year prevalence Scandinavian countries report higher mean estimates than the rest of Europe and Asia. The quality of studies varies greatly but is not correlated with the prevalence estimates. Design varies considerably and standardisation is needed in future studies.

Asia↗
PubMed2005

The relative importance of genetic and environmental factors in the aetiology of thyroid nodularity: a study of healthy Danish twins.

BACKGROUND: A large proportion of healthy, euthyroid, nongoitrous individuals have thyroid nodules. The aetiology of these ultrasonographically detected morphological abnormalities is largely unknown. Factors such as age, gender, iodine intake, smoking and parity are associated with nodularity of the thyroid. Whether there is a genetic susceptibility is unclear. AIM: To gain insight into the aetiology of thyroid nodularity by investigating a large cohort of healthy euthyroid monozygotic and dizygotic twins. DESIGN: A cross-sectional twin study. PARTICIPANTS: A representative sample of self-reported healthy twin pairs was identified through the Danish Twin Registry. A total of 520 individuals divided into 104 monozygotic (MZ), 107 dizygotic same sex (DZ) and 49 opposite sex (OS) twin pairs were investigated. MEASUREMENTS: Probandwise concordance and tetrachoric correlations. Quantitative genetic modelling was used to elucidate the relative importance of genetic and environmental effects for the variation in the liability of nodularity. RESULTS: A higher concordance rate for thyroid nodularity was found in MZ twins [0.57 (95% CI 0.36-0.76)] than in DZ twins [0.36 (95% CI 0.17-0.56, P = 0.074)]. The same was true for tetrachoric correlations: 0.67 (95% CI 0.34-0.87) in MZ twins and 0.17 (CI - 0.28-0.56, P = 0.053) in DZ twins. The difference, although not significant, was more pronounced for multiple nodules than for solitary nodules. Controlling for covariates (age, gender and smoking habits), it was calculated that genetic factors accounted for 67% (95% CI 35-87%) and environmental factors for 33% (95% CI 13-65%) of the individual differences in the liability to thyroid nodularity. CONCLUSIONS: This study suggests that genetic factors are of aetiological importance for thyroid nodularity in clinically healthy and euthyroid individuals, and indicates a difference in the aetiology of solitary and multiple thyroid nodules.

Adult↗
PubMed2005

Risk for multiple sclerosis in dizygotic and monozygotic twins.

We investigated the risks of twins for multiple sclerosis (MS). Our data are linked registers of all Danish twins and of all Danes born between 1920 and 1970 in whom MS was diagnosed before 1997. We compared differences in the risks for MS by Cox regression and standardized incidence ratios. Our analyses suggest that dizygotic twins have an approximately 60% lower risk for MS than monozygotic twins and a 20% lower risk than singletons. Monozygotic twins appear to have a somewhat higher risk for MS than singletons albeit not statistically significant. We offer no biological explanation for our findings, but suggest that either sharing fetal life with a genotypically different individual is beneficial for the immune system or that there is a linkage between the genes that influence dizygotic twinning and other genes that protect against MS.

Adult↗
PubMed2004

Comorbidity with low back pain: a cross-sectional population-based survey of 12- to 22-year-olds.

STUDY DESIGN: Cross-sectional, population-based survey. OBJECTIVES: To investigate the pattern of comorbidity with low back pain in adolescents. SUMMARY OF BACKGROUND DATA: Low back pain is usually dealt with as a specific and independent entity. However, the existing literature shows comorbidity to be common with low back pain, suggesting that low back pain may be part of a broader pattern of general health. The present knowledge is based on studies of adult populations; therefore, associations could be explained by work and lifestyle factors. Information in this area is lacking regarding subjects still unaffected by such factors. METHODS: A questionnaire-survey about general health, including low back pain, was carried out among twins registered in the population-based Danish Twin Registry. Associations between disorders were calculated and patterns of comorbidity investigated, by means of logistic regression and a finite mixture model. Finally a twin-control study was conducted. RESULTS: A total of 9,567 individuals, 12 to 22 years of age, responded to the questionnaire. Positive associations between low back pain and asthma and headache/migraine were demonstrated, mainly because of study participants with several disorders. No association between low back pain and atopic dermatitis/hay fever was found. The presence of two other disorders increased the probability of low back pain considerably more than the presence of only one other disorder. The finite mixture model indicated that the probability of belonging to a frail subgroup decreased from 60% at age 13 to 25% at age 21, and in the frail subgroups nearly all report low back pain and headache in the older ages. Furthermore, increasing duration of low back pain increased the likelihood of having other disorders. Results from the twin-control study were similar. CONCLUSION: Young people are more likely to suffer from asthma and headache, but not from atopic dermatitis/hay fever, if they have low back pain. All of the investigated disorders cluster in some individuals. A model of common origin for these seemingly independent disorders should be considered.

Adolescent↗