Therefore, the major source of variation is genetic, and the location of the relevant genes can be assessed from the linkage analysis carried out on a subset of the dizygotic
And nondependent people at intermediate genetic risk who had dizygotic
co-twins with histories of alcohol dependence had scores that fell between the two former high-risk groups and the control group (Heath et al.
The sequential cohort study included data from 749 monozygotic twin pairs and 687 dizygotic
twin pairs between the age of 8 and 17 and their parents.
The probability that a dizygotic
twin with IBS would have a mother with IBS was greater than the chance that the twin would have a cotwin with IBS (Gastroenterology 121:799-804, 2001).
Interestingly, in patients younger than 50, concordance was dramatically different between monozygotic twins (where four of four twin pairs were concordant) and dizygotic
twins (where only 2 of 12 twin pairs were concordant).
The presence of a genetic factor in schizophrenia is well documented by twin studies and adoption studies: Concordance rates are significantly higher among monozygotic than dizygotic
twins, and prevalence of the disorder is higher among biologic than adoptive relatives of probands.
This analysis, like all studies based on twin pairs reared together, depends on the assumption that environments are equally similar for monozygotic and dizygotic
1) Though it can occur in dizygotic
gestation most commonly seen in monozygotic twinning.
Moderate to substantial genetic influences and modest to moderate environmental influences on substance use appeared in a study of 345 monozygotic (MZ) and 337 dizygotic
(DZ) twin pairs, aged 12-19 years.
twinning, the prevalence of MZ twinning has been remarkably constant worldwide (Dunn and Macfarlane 1996; Guttmacher 1953; Hur et al.
That ADHD is highly influenced by genetic factors has been suggested by repeated twin studies, all of which have found much higher concordance in monozygotic than dizygotic
There is a 100-150 times increased risk in monozygotic twins, but no such association has been found in cases of dizygotic