Biomedical subjects

Meike Bartels

Publications and source records attributed to Meike Bartels.

17 recordsLinked to original sources

PubMed2026

ENLIGHTENme: Translating the Benefits of Self-Administered Daytime Light Supplementation to Older Adults in the Real World.

Controlled studies have demonstrated that light supplementation benefits circadian entrainment, sleep and mood. Translating these findings into effective, real-world usage of light supplementation is, however, challenging because naturalistic and supplemental light exposure are shaped by personal habits and environmental light conditions. Bridging this translation gap is especially critical for older adults, given the reduced ocular light sensitivity associated with natural ageing, which exacerbates low daytime indoor light exposure in urban housing. We therefore set out to investigate the determinants of self-directed light supplementation in this population, and what the real-world feasibility and efficacy of daytime light supplementation is. We recruited 202 participants (63-92 years; 139 females) to our interventional, prospective, randomised study in three major EU cities at different latitudes (Amsterdam, Bologna, Tartu). Participants underwent a 2-week baseline assessment of light exposure, rest-activity patterns and sleep through wearables and daily diaries. Participants were then randomised to either 12 weeks of self-implemented indoor light supplementation using a lamp placed in their most frequently used room (> 8000 melanopic EDI, N = 98) or a no-intervention group. A subsequent 2-week reassessment showed that greater naturalistic light exposure was associated with increased daytime activity, consolidated wakefulness, better subjective sleep quality, and reduced metabolic disorder incidence. Individuals with lower naturalistic light exposure self-initiated earlier and longer indoor light supplementation across seasons, in which supplementation onset before 10:00 was associated with greater daytime activity and lower rest-activity fragmentation. These results confirm that this simple, non-pharmacological, and low-cost intervention has broad potential to support healthy ageing in urban settings.

Humans↗

PubMed2025

Genome-wide association meta-regression identifies stem cell lineage orchestration as a key driver of acne risk.

Over 85% of the population experience acne at some point in their lives, with its severity spanning a quantitative spectrum, from mild, transient outbreaks to more persistent, severe forms of the condition. Moderate to severe disease poses a substantial global burden arising from both the physical and psychological impacts of this highly visible condition. The analytical approach taken in this study aimed to address the impact of variation in the dichotomisation of acne case control status, driven by ascertainment and study design, on effect size estimates across independent genetic association studies of acne. Through a fixed intercept meta-regression framework, we combined evidence genome-wide for association with acne across studies in which case-control status had been ascertained in different settings, allowing for different severity threshold definitions. Across a combined sample of 73,997 cases and 1,103,940 controls of European, South Asian and African American ancestry we identify genetic variation at 165 genomic loci that influence acne risk. There is evidence for both shared and ancestry specific components to the genetic susceptibility to acne and for sex differences in the magnitude of effect of risk alleles at three loci. We observe that common genetic variation explains 13.4% of acne heritability on the liability scale. Consistent with the hypothesis that genetic risk primarily operates at the level of individual pilosebaceous units, a polygenic score derived from this case-control study of acne susceptibility is associated with both self-reported and clinically assessed acne severity in adolescence, further strengthening the link between genetic risk and disease severity. Prioritisation of causal genes at the identified acne risk loci, provides genetic validation of the targets of established and emerging acne therapies, including retinoid treatments. The identified acne risk loci are enriched for genes encoding downstream effectors of RXRA signalling, including SOX9 and components of the WNT and p53 pathways. Illustrating that the control of stem cell lineage plasticity and cellular fate are important mechanisms through which genetic variation influences acne susceptibility within the pilosebaceous unit.

Journal Article↗

PubMed2006

Genetic and environmental contributions underlying stability in childhood obsessive-compulsive behavior.

BACKGROUND: Little is known about the stability of obsessive-compulsive (OC) behavior during childhood. The objective of this study is to determine the developmental stability of pediatric OC behavior and the genetic and environmental influences on stability in a large population-based twin sample. METHODS: Maternal and paternal ratings on the 8-item Obsessive Compulsive Scale of the Child Behavior Checklist (CBCL-OCS) on Dutch mono- and dizygotic twin pairs from 8083 families were collected at ages 7, 10, and 12 years. Using a longitudinal twin design, stability of OC behavior and genetic and environmental influences on stability were determined. Using cutoff criteria, persistent, resilient, and new onset cases were identified in this sample. RESULTS: OC behavior assessed by the CBCL-OCS showed a moderate stability with phenotypic correlations of around .50 for boys and for girls. Stability of OC behavior was influenced by genetic factors, by environmental factors shared by children growing up in the same family, and by non-shared environmental factors. Stability for OCS was lower when categorical data were analyzed than when quantitative definitions were used. CONCLUSIONS: OC behavior is moderately stable in childhood. Stability of OC behavior is influenced by genetic, shared, and non-shared environmental factors.

Child↗

PubMed2006

Individual differences in puberty onset in girls: Bayesian estimation of heritabilities and genetic correlations.

: We report heritabilities for individual differences in female pubertal development at the age of 12. Tanner data on breast and pubic hair development in girls and data on menarche were obtained from a total of 184 pairs of monozygotic and dizygotic twins. Genetic correlations were estimated to determine to what extent the same genes are involved in different aspects of physical development in puberty. A Bayesian estimation approach was taken, using Markov-chain Monte Carlo simulation to estimate model parameters. All three phenotypes were to a significant extent heritable and showed high genetic correlations, suggesting that a common set of genes is involved in the timing of puberty in general. However, gonadarche (menarche and breast development) and adrenarche (pubic hair) are affected by different environmental factors, which does not support the three phenotypes to be regarded as indicators of a unitary physiological factor.

Bayes Theorem↗

PubMed2006

The heritability of perceived stress.

BACKGROUND: Exploration of the degree to which perceived chronic stress is heritable is important as these self-reports have been linked to stress-related health outcomes. The aims of this study were to estimate whether perceived stress is a heritable condition and to assess whether heritability estimates vary between subjective stress reactivity and stress related to external demands. METHOD: A sample of 103 monozygotic and 77 dizygotic twin pairs completed three questionnaires designed to measure perceived stress: the Perceived Stress Scale (PSS), the Measure for the Assessment of Stress Susceptibility (MESA) and the Trier Inventory for the Assessment of Chronic Stress (TICS). The TICS assesses the frequency of stressful experiences on six scales, the MESA assesses subjective stress reactivity, and the PSS takes both factors into account. RESULTS: A multivariate model-fitting procedure revealed that a model with common additive genetic and shared environmental factors best fit the eight scales (PSS, MESA, six TICS scales). Heritabilities for the best-fitting model varied between 5% and 45%, depending on the scale. CONCLUSIONS: The present data suggest that perceived stress is in part heritable, that nearly half of the covariance between stress scales is due to genetic factors, and that heritability estimates vary considerably, depending on the questionnaire. Beyond methodological considerations that pertain to the validity of the questionnaires, these data suggest that studies assessing the heritability of perceived chronic stress should take the specific questionnaire focus into account.

Adult↗

PubMed2006

Five types of personality continuity in childhood and adolescence.

This study examines 5 types of personality continuity--structural, mean-level, individual-level, differential, and ipsative--in a representative population (N=498) and a twin and sibling sample (N=548) of children and adolescents. Parents described their children on 2 successive occasions with a 36-month interval using the Hierarchical Personality Inventory for Children (I. Mervielde & F. De Fruyt, 1999). There was evidence for structural continuity in the 2 samples, and personality was shown to be largely differentially stable. A large percentage had a stable trait profile indicative of ipsative stability, and mean-level personality changes were generally small in magnitude. Continuity findings were explained mainly by genetic and nonshared environmental factors.

Adolescent↗

PubMed2006

Influences on achieving motor milestones: a twin-singleton study.

In order to determine if twinning impacted achievement of motor milestones the attainment of early motor milestones in twins was examined and compared to published data from singletons of the same age from the same culture and birth years. We examined the influence of twinning, sex, zygosity and birth cohort (1987-2001) on the motor development of twins aged 0 to 24 months. Data on the attainment of motor milestones (turn, sit, crawl, stand and walk) of twins were collected from maternal reports. All data were corrected for gestational age. Data from the twin sample were compared to normative data from singletons, which were available from Child Health Clinics (CHC). Analyses across twin data and the CHC singleton data revealed no differences between twins and singletons in achievement of motor milestones. Girls were able to sit without support slightly earlier than boys, otherwise there were no other sex differences. Birth-order analyses revealed minimal but significant differences in turning over from back to belly and for sitting without support between the first- and second-born. Dizygotic (DZ) twins were faster than monozygotic (MZ) twins in achieving the moment of sit, crawl, stand and walk. Twins born in earlier cohorts were faster in reaching the moment of crawl, sit and walk. It is concluded that there are no differences in time of reaching motor milestones between twins and singletons within the normal range. Sex has minimal to no effect on motor development in early childhood. DZ twins achieve motor milestones sooner than MZ twins. Attainment of gross motor milestones (crawl, stand and walk) is delayed in later birth cohorts.

Analysis of Variance↗

PubMed2006

Heritability of testosterone levels in 12-year-old twins and its relation to pubertal development.

The aim of this study was to estimate the heritability of variation in testosterone levels in 12-year-old children, and to explore the overlap in genetic and environmental influences on circulating testosterone levels and androgen-dependent pubertal development. Midday salivary testosterone samples were collected on 2 consecutive days in a sample of 183 unselected twin pairs. Androgen-induced pubertal development was assessed using self-report Tanner scales of pubic hair development (boys and girls) and genital development (boys). A significant contribution of genetic effects to the variance in testosterone levels was found. Heritability was approximately 50% in both boys and girls. The remaining proportion of the variance in testosterone levels could be explained by nonshared environmental influences. The relatively high correlation between testosterone levels of opposite-sex dizygotic twins suggests that sex differences in genes influencing variation in testosterone levels have not yet developed in pre- and early puberty. Variance in pubertal development was explained by a large genetic component, moderate shared environmental influences, and a small nonshared environmental effect. Testosterone levels correlated moderately (r = .31) with pubertal development; the covariance between testosterone levels and pubertal development was entirely accounted for by genetic influences.

Child↗

PubMed2006

Body size in five-year-old twins: heritability and comparison to singleton standards.

The aim of this study is to examine causes of individual differences in height, weight and body mass index (BMI) in 5-year-old children registered with the Netherlands Twin Register. In addition, we examine whether the results of twin studies can be expanded to the singleton population by comparing the data from twins to Dutch reference growth data and by looking at the twins' target height, which was derived from parental height. For 2996 5-year-old twin pairs, information on height and weight and on parental height was available. Univariate and bivariate genetic analyses of height and weight and univariate analyses of BMI were conducted. In order to compare the twins to the singleton population, standard deviation scores (SDS) for height, BMI and target height were calculated based on Dutch reference growth charts for the general population from 1997. Genetic influences were an important source of variation in height, weight and BMI and the main source of covariation between height and weight. Additive genetic factors accounted for 69% and 66% of the individual differences in height in boys and girls, respectively. For weight, heritability estimates were 59% in boys and 78% in girls and for BMI 34% and 74%. The influence of common environment on height was 25% and 27%, on weight 24% and 10% and on BMI 44% and 12% in boys and girls. The bivariate model showed a large overlap between the genes influencing height and weight. Genes explain 78% (in boys) and 76% (in girls) of the covariance between weight and height. At the age of 5 years, female twins were as tall as singleton children, while male twins were shorter than singletons. For both boys and girls, however, mean height SDS was 0.6 standard deviation scores below the mean target height. All twins had lower BMI than singletons. Twins grow fairly well compared to singletons, but they grow below their target height. This may be due to the above average height of twin parents.

Body Height↗

PubMed2005

Eating disorders: from twin studies to candidate genes and beyond.

Substantial effort has been put into the exploration of the biological background of eating disorders, through family, twin and molecular genetic studies. Family studies have shown that anorexia (AN) and bulimia nervosa (BN) are strongly familial, and that familial etiologic factors appear to be shared by both disorders. Twin studies often focus on broader phenotypes or subthreshold eating disorders. These studies consistently yielded moderate to substantial heritabilities. In addition, there has been a proliferation of molecular genetic studies that focused on Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association, 1994) AN and BN. Seven linkage regions have been identified in genome-wide screens. Many genetic association studies have been performed, but no consistent association between a candidate gene and AN or BN has been reported. Larger genetic association studies and collaborations are needed to examine the involvement of several candidate genes and biological pathways in eating disorders. In addition, twin studies should be designed to assist the molecular work by further exploring genetic determinants of endophenotypes, evaluating the magnitude of contribution to liability of measured genotypes as well as environmental risk factors related to eating disorders. In this manner twin and molecular studies can move the field forward in a mutually informative way.

Anorexia↗

PubMed2005

Genetic contributions to subtypes of aggression.

Boys and girls may display different styles of aggression. The aim of this study was to identify subtypes of aggression within the Child Behavior Checklist (CBCL) aggression scale, and determine their characteristics for both sexes. Maternal CBCL ratings of 7449 7-year-old twin pairs were analyzed using principal components analyses to identify subtypes of aggression, and structural equation modeling to carry out genetic analyses. Two aggression subtypes were identified: relational and direct aggression. The correlation between these subtypes was .58 for boys and .47 for girls. Boys had higher mean scores for both subtypes of aggression, but sex differences were largest for direct aggression. For relational aggression, 66% of the variance was due to additive genetic influences, 16% to shared environment and 18% to nonshared environment. For direct aggression, additive genetic effects accounted for 53% of the variance in males and 60% in females, shared environment explained 23% of the variance in males and 13% in females, and nonshared environmental effects explained 24% of the variance in males and 27% in females. Covariance between the aggression subtypes was mostly accounted for by additive genetic (55% for boys, 58% for girls) and shared environmental influences (33% for boys, 30% for girls). Direct and relational aggression were both influenced by one underlying set of shared environmental factors, but only partly by the same genes (the genetic correlation was .54 for boys and .43 for girls). These findings may have implications for how aggressive behavior should be assessed in boys and girls.

Aggression↗

PubMed2004

Genetic and environmental contributions to the Child Behavior Checklist Obsessive-Compulsive Scale: a cross-cultural twin study.

CONTEXT: We have reported elsewhere on the development of an 8-item Obsessive-Compulsive Scale (OCS) contained in the Child Behavior Checklist (CBCL) to identify children who meet criteria for DSM-IV obsessive-compulsive disorder. Twin studies of obsessive-compulsive disorder have indicated a significant genetic component to its expression. OBJECTIVE: To determine the relative contributions of genetic and environmental influences on childhood obsessive-compulsive behavior using the CBCL OCS in twin samples. DESIGN: The CBCL data were received by survey of twins in the Netherlands Twin Registry (NTR) and the Missouri Twin Study (USA/MOTWIN). SETTING: General community twin samples. PARTICIPANTS: Participants were 4246 twin pairs aged 7 years, 2841 aged 10 years, and 1562 aged 12 years (who also participated in the study at 7 and 10 years of age) from the NTR and 1461 mixed-age twin pairs (average age, approximately 9 years) from the USA/MOTWIN. MAIN OUTCOME MEASURES: Model fitting to test for genetic and environmental influences, sex differences, and sibling interaction/rater contrast effects on the CBCL OCS. RESULTS: In each case, the best-fitting model was one that indicated significant additive genetic influences (range, 45%-58%; 95% confidence interval [CI], 45%-61%), and unique environmental influences (range, 42%-55%; 95% CI, 39%-55%), with shared environmental influences in the NTR sample aged 12 years (16%). Sex differences were seen in the mixed-age USA/MOTWIN model, but not in the NTR samples. No evidence of dominance, sibling interaction, or rater-contrast effects was seen. These data were relatively consistent across age and cultures. CONCLUSIONS: The CBCL OCS is influenced by genetic factors (approximately 55%) and unique environmental factors (approximately 45%) in the younger sample, with common environmental influences only at 12 years of age. These effects do not vary with differences in sex or sibling interaction/rater contrast effects. Our data reveal higher genetic influences for obsessive-compulsive behavior and do not demonstrate genetic differences across sex.

Age Factors↗

PubMed2004

Disentangling genetic, environmental, and rater effects on internalizing and externalizing problem behavior in 10-year-old twins.

Previous studies have emphasized the importance of rater issues in studying the etiology of variation in internalizing and externalizing problems in children. Earlier results indicate only moderate agreement between parents, and assume that parents assess a specific aspect of their child's behavior. In comparable samples of younger children, additive genetic effects are the main factor explaining individual differences in both internalizing and externalizing behavior. It is unknown whether this pattern of rater influences and variance decomposition will be consistent in older children. Child Behavior Checklists (Achenbach, 1991), completed by both parents, were collected in a sample of 2956 Dutch 10-year-old twin pairs. The etiology of individual differences in internalizing and externalizing syndromes was examined using a model that corrected for possible rater bias, rater-specific effects and unreliability. The best fitting model suggested that disagreement between the parents is not merely the result of unreliability and/or rater bias, but each parent also provides specific information from his/her own perspective on the child's behavior. Significant influences of additive genetic, shared environmental and unique environmental factors were found for internalizing and externalizing syndromes.

Child↗

PubMed2003

Heritability of daytime cortisol levels in children.

Individual differences in the level of the stress hormone cortisol play a prominent role as an explanatory variable in studies on psychopathology. Relatively few studies have paid attention to individual differences in cortisol levels and the etiology of these differences, in particular their possible genetic basis. All these studies have been in adults. The aim of this study was to estimate genetic and environmental influences on basal cortisol levels in 12-year-old children. To this end, four samples of salivary cortisol were collected on two consecutive days in a sample of 180 twin pairs. Low correlations were found between cortisol levels at different points in time during the day. A significant genetic contribution was found to the variation of basal cortisol levels in the morning and afternoon samples, but not in the evening sample. Heritability did not differ for boys and girls and was highest (60%) for cortisol levels during the sample taken about 45 minutes after awakening. This cortisol awakening response provides a useful endophenotype in the search for genes that may affect hypothalamic-pituitary adrenocortical functioning in children.

Biomarkers↗

PubMed2003

A study of parent ratings of internalizing and externalizing problem behavior in 12-year-old twins.

OBJECTIVE: Studies on 3-, 7-, and 10-year-old twins' internalizing and externalizing problems have emphasized the importance of understanding sources of agreement and disagreement between maternal and paternal ratings. A psychometric model that assumes that each parent assesses rater-specific aspects of the child's behavior provided the best explanation for parental disagreement. This study investigates two models that have been used to explain the agreement and disagreement between mothers and fathers in the ratings of their children. METHOD: Child Behavior Checklists filled in by mothers and fathers were collected for a sample of 1,481 twelve-year-old twin pairs. Genetic and environmental influences on internalizing and externalizing problems were estimated using models that corrected for rater bias, rater-specific effects, and unreliability. RESULTS: The psychometric model fitted the data significantly better than a rater bias model. Significant influences of genetic, shared, and nonshared environmental factors were found for internalizing and externalizing behavior. Parent-specific views, rater bias, and unreliability were significant. CONCLUSIONS: The best-fitting model implies that disagreement between parents is due to the fact that mothers and fathers provide information from their own perspective. This information should be seen as important and adding to the diagnostic formulation rather than as a point of disagreement. The finding that internalizing and externalizing problems are influenced by genetic and environmental factors fosters the understanding that it is the interaction of nature and nurture that puts children at risk for common behavioral disorders.

Adolescent↗

PubMed2002

Netherlands Twin Register: a focus on longitudinal research.

In 1986 we began The Netherlands Twin Register (NTR) by recruiting young twins and multiples a few weeks or months after birth. Currently we register around 50% of all newborn multiples in The Netherlands. Their parents receive a questionnaire at registration and afterwards when the children are 2, 3, 5, 7, 10 and 12 years of age. Teachers are asked to rate the behavior of the children at ages 7, 10 and 12 years. Adolescent and young-adult twins were recruited through City Councils in the early 1990s. These twins, their parents and siblings participate in longitudinal survey studies that include items about health, fertility, lifestyle, addiction, personality and psychopathology, religion, socioeconomic status, and educational attainment. The total number of twins and multiples registered with the NTR is currently over 60,000. Subgroups of twins and siblings take part in studies of cognitive development, brain function and neuropsychological indices of attention processes, and molecular genetic studies of classical and behavioral cardiovascular risk factors. DNA samples are currently collected in selected twin families for two large linkage studies, which aim to find QTLs for anxious depression and for nicotine addiction. Sisters who are mothers of DZ twins contribute DNA samples for a linkage study of DZ twinning. Large cohorts of phenotyped family members from the general population are very valuable for genetic epidemiological studies and permit selection of informative families for gene finding studies.

Adolescent↗

PubMed2002

Heritability of educational achievement in 12-year-olds and the overlap with cognitive ability.

In order to determine high school entrance level in the Netherlands, nowadays, much value is attached to the results of a national test of educational achievement (CITO), administered around age 12. Surprisingly, up until now, no attention has been paid to the etiology of individual differences in the results of this national test of educational achievement. No attempt has been made to address the question about the nature of a possible association between the results of the CITO and cognitive abilities, as measured by psychometric IQ. The aim of this study is to explore to what extent psychometric IQ and scholastic achievement, as assessed by the CITO high school entrance test, are correlated. In addition, it was investigated whether this expected correlation was due to a common genetic background, shared or nonshared environmental influences common to CITO and intelligence or a combination of these influences. To this end multivariate behavior genetic analyses with CITO and IQ at ages 5, 7, 10 and 12 years have been conducted. The correlations were.41,.50,.60, and.63 between CITO and IQ assessed at age 5, 7, 10, and 12 respectively. The results of the analyses pointed to genetic effects as the main source of variance in CITO and an important source of covariance between CITO and IQ. Additive genetic effects accounted for 60% of the individual differences found in CITO scores in a large sample of Dutch 12-year-olds. This high heritability indicated that the CITO might be a valuable instrument to assess individual differences in cognitive abilities in children but might not be the right instrument to put the effect of education to the test.

Child↗