The classical twin study, wherein the similarity of monozygotic (MZ) twins is compared with that of dizygotic (DZ) twins to estimate the heritability of a trait (proportion of total Variance due to genetic

Identical (monozygotic) twins have attracted special attention for the study of behavior genetics. Some of the assumptions and results of these studies are reviewed with special attention given to the natural experiment of identical twins adopted by different families. However, the correlation for any behavior between the adopted twins of a monozygotic pair is affected by their common prenatal ...

OBJECTIVE Monozygotic twins are usually discordant (only one twin affected) for type 1 diabetes. Discordance for disease between such twins implies a role for nongenetically determined factors but could also be influenced by a decreased load of diabetes susceptibility genes. The aim of this study was to determine whether two susceptibility genes were less prevalent in discordant twins compared ...

BACKGROUND Atrial fibrillation (AF) is a common arrhythmia. Several studies have shown association of genetic variants with AF and that familial AF increases the risk of AF. We have previously shown a substantial heritability of AF in a twin study. The objective of this study was to determine whether having a co-twin with AF influences mortality. METHODS AND RESULTS We identified all Danish t...

We report monozygotic twins with longitudinal radial hypoplasia and low (L5) spina bifida occulta, but with differing severity. There is only one previous report of similar twins. We report these identical twins with the expression of longitudinal radial hypoplasia with mirror image pattern on contralateral sides, and the association of low spina bifida occulta.

The occurrence of trisomy 13 in twins is very rare. We report a pair of genotypically identical twins with trisomy 13 discordant for major anomalies. This case contributes to the already published data on the contribution of non-genetic factors to the aetiology of congenital malformations in monozygotic twins.

Purpose To determine the genetic contribution to the pattern of retinal vascular branching expressed by its fractal dimension. Methods This was a cross-sectional study of 50 monozygotic and 49 dizygotic, same-sex twin pairs aged 20 to 46 years. In 50°, disc-centered fundus photographs, the retinal vascular fractal dimension was measured using the box-counting method and compared within monozy...

We report a case of discordant phenotypic sex in monozygotic twins mosaic 47,XXY/46,XX: monozygotic heterokaryotypic twins. The twins presented with cognitive and comprehension delay, behavioural and language disorders, all symptoms frequently reported in Klinefelter syndrome. Molecular zygosity analysis with several markers confirmed that the twins are in effect monozygotic (MZ). Array compara...

STUDY DESIGN Clinical, radiological, and genetic determination of zygosity of twin pairs from the Danish Twin Registry who self-reported having adolescent idiopathic scoliosis (AIS). OBJECTIVE To establish concordance rates of AIS. SUMMARY OF BACKGROUND DATA The etiology of and the true mode of inheritance of AIS remain unclear. Studies on concordance in twin pairs provide a basis for analy...

BACKGROUND Hereditary pancreatitis (HP) is a rare autosomal dominant disorder with variable expression and an overall lifetime penetrance of 80%. We hypothesised that (1) monozygotic twins within similar environments would develop the typical signs of HP at a similar age, and (2) if penetrance were due to modifier genes or environment, all twin pairs would be concordant for expression of HP. ...