Jacob F. Orlebeke

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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)
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)
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)
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)
OBJECTIVE To compare blood pressure-regulating mechanisms during mental stress in two groups of offspring with contrasting risk for hypertension. DESIGN Cardiovascular reactivity to two different types of mental stressors was studied in adolescents and young adults with two hypertensive or two normotensive parents. The two tasks used were intended to(More)
This study evaluates the effects of vitamin B-6 supplementation (20 mg pyridoxine HCL daily for 3 months) on mood and performance in 38 self-supporting healthy men, aged between 70–79 years. Effects were compared with 38 controls who received placebo and were matched for age, plasma pyridoxal-5′-phosphate (PLP) concentration and intelligence score. Before(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)
Twin-singleton differences in problem behaviours in 2-3-year-olds were studied. Maternal ratings of children's problem behaviours were obtained with the CBCL/2-3. The twin sample consisted of 1363 twin pairs (456 MZ, 907 DZ), the sample of singletons consisted of 420 children from the general population. Results indicated that the general level of problem(More)