Learn More
In a study of 1600 Dutch adolescent twin pairs we found that 59% of the inter-individual variation in smoking behaviour could be attributed to shared environmental influences and 31% to genetic factors. The magnitude of the genetic and environmental effects did not differ between boys and girls. However, environmental effects shared by male twins and(More)
The inheritance of spontaneous dizygotic (DZ) twinning was investigated in 1,422 three-generation pedigrees ascertained through mothers of spontaneous DZ proband twins. DZ twinning was modelled as a trait expressed only in women. The penetrance was modelled first as a parity independent and secondly as parity dependent. The observed frequencies of maternal(More)
The effects of tyrosine on mood, performance, heart rate and blood pressure of 16 healthy young subjects were assessed. Subjects were tested on two separate days, one test session after ingestion of 100 mg/kg tyrosine and the other test session after placebo, in random order. While performing a number of stress sensitive tasks, subjects were exposed to a(More)
The Netherlands Twin Register (NTR) began in 1987 with data collection in twins and their families, including families with newborn twins and triplets. Twenty-five years later, the NTR has collected at least one survey for 70,784 children, born after 1985. For the majority of twins, longitudinal data collection has been done by age-specific surveys. Shortly(More)
A pilot study was carried out to investigate the relationship between exposure to lead and attention in children. The participants were 43 boys, 8 to 12 years of age, attending special schools for children with educational and/or learning problems (so called LOM schools). Children with probable causes of attentional or memory problems other than lead(More)
Men and women differ in temperament and personality traits, such as aggression and sensation seeking. The sex hormone testosterone could play a role in the origin of these differences, but it remains unclear how and when testosterone could have these effects. One way to investigate the prenatal exposure effect of testosterone is to compare opposite-sex (OS)(More)
A model to analyze resemblances of twins and parents using LISREL is outlined and applied to sports participation and heart-rate data. Sports participation and heart rate were measured in 44 monozygotic and 46 dizygotic adolescent twin pairs and in their parents. Genetic factors influence variation in both sports behavior and heart rate, while there is no(More)
Respiratory sinus arrhythmia (RSA) has been shown to be a sensitive index of vagal cardiac control. We studied the genetic and nongenetic influences on individual differences in RSA in a sample of 160 adolescent twins. RSA was measured during rest and across two different tasks. Results show that heritability is task dependent. The amount of genetic(More)
The primary goal of the present study was to examine whether in the elderly with mild cognitive impairment (MCI), the effect of physical activity measured directly following treatment, was reflected in an improvement in cognitive functioning in general or in executive functions (EF) in particular. Secondly, this study aimed to compare the effectiveness of(More)