Genetics of parentally reported asthma, eczema and rhinitis in 5-yr-old twins.

The aim of the present study was to examine the genetic and environmental contributions to the individual differences in susceptibility to asthma, eczema and rhinitis in childhood and their role in the association among these conditions. Information on asthma, eczema and rhinitis was obtained by parental report. Parents were asked whether a physician had ever diagnosed the condition. Complete data were available for 8,633 5-yr-old twin pairs born between 1986 and 1998. The frequency of parentally reported asthma, eczema and rhinitis was 8.7, 16.8 and 4.4%, respectively, and was higher in males than females. Genetic factors accounted for ∼90% of the variance in the susceptibility to asthma, eczema and rhinitis. The magnitude of genetic factors did not differ between males and females. The remaining part of the variance was explained by environmental factors not shared by family members. The phenotypic correlations between parentally reported asthma, eczema and rhinitis were moderate and mainly mediated by the same genetic factors. The high heritability and the limited influence of shared environmental factors may point to gene x environment interactions. Future research should focus on this type of interaction processes. Copyright © ERS Journals Ltd 2007

Genetics of the human electroencephalogram (EEG) and event-related brain potentials (ERPs): a review

Twin and family studies of normal variation in the human electroencephalogram (EEG) and event related potentials (ERPs) are reviewed. Most of these studies are characterized by small sample sizes. However, by summarizing these studies in one paper, we may be able to gain some insight into the genetic influences on individual differences in central nervous system functioning that may mediate genetically determined differences in behavior. It is clear that most EEG parameters are to a large extent genetically determined. The results for ERPs are based on a much smaller number of studies and suggest medium to large heritability. © 1994 Springer-Verlag

Comparison of Naturally Conceived and IVF-DZ Twins in the Netherlands Twin Registry: A Developmental Study

In a large set of twin pairs, we compared twins born after IVF to naturally conceived twins with respect to birth characteristics, growth, attainment of motor milestones, and emotional and behavioral problems. Twin families were registered with the Netherlands Twin Register. We included 1534 dizygotic (DZ) twins born after IVF, 5315 naturally conceived (NC) DZ twins, and 1504 control NC DZ twins who were matched to the IVF twins based on maternal age, maternal educational level, smoking during pregnancy, gestational age, and offspring sex. Data were obtained by longitudinal surveys sent to fathers, mothers, and teachers at ages 1, 2, 3, 7, 10, and 12 years. Results showed no differences in growth, in attainment of motor milestones, and in behavioral development between IVF and matched NC twins. It can be concluded that for nearly all aspects, development in IVF and NC children is similar

Genetic and environmental influences on cross-gender behavior and relation to behavior problems: A study of Dutch twins at ages 7 and 10 years.

The aim of this study was to investigate the prevalence of cross-gender behavior during childhood, to estimate the influence of genotype and environment on variation in cross-gender behavior, and to explore the association of cross-gender behavior with maternal ratings of behavior problems as indexed by the Internalizing and Externalizing scales of the Child Behavior Checklist (CBCL). Cross-gender behavior was assessed by two items from the CBCL: "behaves like opposite sex" and "wishes to be of opposite sex." As part of an ongoing longitudinal study of the Netherlands Twin Registry, mothers were asked to complete the CBCL for their twins when they were 7 (n∼14,000 twins) and 10 years old (n∼8,500 twins). The prevalence of cross-gender behavior (as measured by maternal report of behaving like or wishing to be the opposite sex) was 3.2% and 5.2% for 7-year-old boys and girls, respectively, and decreased to 2.4% and 3.3% for 10-year-old boys and girls. Surprisingly, the prevalence rate of cross-gender behavior of girls with a male co-twin was lower than of girls with a female co-twin. At both ages, the similarity for cross-gender behavior was greater in monozygotic than in dizygotic twins pairs. Genetic structural equation modeling showed that 70% of the variance in the liability of cross-gender behavior could be explained by genetic factors, at both ages and for both sexes. Cross-gender behavior was associated with higher scores on Internalizing and Externalizing problems, both in boys and in girls. © 2006 Springer Science+Business Media, Inc

Causes of stability of aggression from early childhood to adolescence: A longitudinal genetic analysis in Dutch twins

Aggressive behavior (AGG) in childhood is a stable behavioral trait that persists to a considerable degree into adulthood. For example, Verhulst and van der Ende (1995) investigated the developmental course of proble

Effects of twin separation in primary school

We studied the short- and long-term effects of classroom separation in twins on behavior problems and academic performance. Short-term effects were studied at age 7 in twins separated at age 5 and long-term effects at age 12 in twins who had been separated or together most of the time at school. Behavior problems were rated by mothers (Child Behavior Checklist at ages 3, 7 and 12) and teachers (Teacher Report Form at ages 7 and 12). Academic achievement was measured at age 12 using a national academic achievement test (CITO). At age 7, twins from separated pairs had more internalizing and externalizing problems than non-separated twins, as rated by both mothers and teachers. Only for the maternal ratings of internalizing problems, however, could these effects be attributed to the separation itself and not to preexisting problems (at age 3) between separated and nonseparated twins. Long-term effects of separation were significant for maternal and teacher ratings of internalizing and externalizing problems, but these effects could be explained by preexisting differences between separated and nonseparated groups. There were no differences in academic achievement between the separated and nonseparated group. These results suggest that the decision to separate twins when they go to school is based in part on the existing behavioral problems of the twins and that, in the long run, separation does not affect problem behavior or academic achievement. The findings were the same for monozygotic and dizygotic twins

Genetic contributions to the association between height and intelligence: Evidence from Dutch twin data from childhood to middle age.

A positive association between intelligence (IQ) and height has been reported previously. It is generally assumed that this association reflects the effect of childhood environment on IQ, but there is still little research supporting directly this hypothesis. We studied the association between height and IQ in 209 Dutch twin pairs at the ages of 5, 7, 10 and 12 years, 208 twin pairs at 16 and 18 years of age and 567 twin pairs and their siblings in adulthood. The heritability of height was high in all cohorts and across all ages (

Heritability of self-reported asthma and allergy: A study in adult Dutch twins, siblings and parents.

The present study assessed the prevalence of asthma and allergy, and estimated the importance of genetic and environmental influences on asthma and allergy liability and their association. Longitudinal data on self-reported, doctor-diagnosed asthma and allergy were collected in over 14,000 individuals registered with the Netherlands Twin Register. Structural equation modeling was used for univariate and bivariate genetic analyses on data from twins, their siblings, and parents. Results showed no sex, age, and minimal birth cohort effects for asthma prevalence (11.8%). For allergy, prevalence was higher in women (19.8%) than in men (13.9%). Allergy prevalence at ages 22, 23, and 24 years increased from the 1970 to the 1980 birth cohort. The prevalence of allergy, but not of asthma, was higher in nontwin siblings than in twins. No assortative mating was observed. High (broad-sense) heritabilities were found for asthma (75%) and allergy (66%), with evidence for nonadditive genetic effects in asthma. The association between asthma and allergy (correlation = .65) was largely due to common genes (70%). No sex differences in genetic architecture were found. In conclusion, the prevalence of allergy but not of asthma increased in recent years. Individual differences in the liability to asthma, allergy and their co-occurrence are for a large part accounted for by differences in genetic background. Nonadditive gene action is important, which may have consequences for gene hunting strategies

A genetic perspective on the developing brain: electrophysiological indices of neural functioning in young and adolescent twins.

Changes in genetic and environmental influences on electroencephalographic (EEG) and event-related potential (ERP) indices of neural development were studied in two large cohorts of young (N = 418) and adolescent (N = 426) twins. Individual differences in these indices were largely influenced by genetic factors, and throughout development, the stable part of the variance was mainly genetic. Both EEG power (which describes the amount of variability in brain electrical potentials that can be attributed to different frequencies) and long-distance EEG coherence (which is the squared cross-correlation between two EEG signals at different scalp locations and can be regarded as an index for cortico-cortical connectivity) were highly heritable. ERP-P300 latencies and amplitudes were low to moderately heritable. Clear differences between young children and adolescents could be observed in the heritabilities of EEG and ERP indices. The heritabilities of EEG power and EEG coherence were higher in adolescents than in children, whereas the heritabilities of P300 latencies were lower. Both cohorts (young children and adolescents) were measured twice: The children were tested when they were 5 and again at 7 years, the adolescents when they were 16 and again at 18 years. Therefore, within these age ranges a more detailed analysis of age-related changes in heritabilities and in the emergence of new genetic influences could be studied. The heritabilities of EEG powers and P300 amplitudes and latencies did not change much from age 5 to age 7 and from age 16 to 18 years. The heritabilities of a substantial number of connections within the cortex, however, as indexed by EEG coherence, changed significantly from age 5 to age 7, though not from age 16 to 18. The only changes in the heritabilities in adolescents were connections within the prefrontal cortex, which is in agreement with theories of adolescent development. These age-related changes in the heritabilities may reflect a larger impact of maturation on cortico-cortical connectivity in childhood than in adolescence. Evidence was found for qualitative changes in brain electrophysiology in young children: New genetic factors emerged at age 7 for posterior EEG coherences and for P300 latency at some scalp locations. This supports theories of qualitative stage transitions in this age range, as previously suggested using behavioral and EEG data

Stability of genetic and environmental influences om P300 amplitude: a longitudinal study in adolescent twins

Examined the stability of genetic and environmental influences on individual differences in P300 amplitude during adolescence. The P300 component is an event-related brain potential (ERP) that has attracted much attention as a biological marker for disturbed cognitive processing in psychopathology. Understanding the genetics of this biological marker may contribute to understanding the genetics of the associated psychopathologies. In a group of 213 adolescent twin pairs, the P300 component was measured twice, the first time at age 16 and the second time 18 months later. A large part of the variance of the P300 amplitude could be explained by familial factors, with estimates ranging from 30% to 81%. Whether the familial resemblance was due to genetic or shared environmental factors depended on sex. For males, genetic factors explained familial resemblance in P300 amplitude, but for females such resemblance was likely due to shared environmental factors. The phenotypic stability of the P300 amplitude from 16 to 18 years was high in both sexes, and stability could be attributed largely to the same familial factors. There was no evidence that new familial influences emerged at age 18