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Individuals with ADHD, as well as their family members who do not meet clinical criteria, have shown deficits in executive function. However, it remains unclear whether underlying neural alterations are familial or ADHD-specific. To investigate this issue, neural activation underlying executive function was assessed using functional magnetic resonance imaging during performance of a Stroop task in three groups of individuals: 20 young adults who were diagnosed with ADHD in childhood, their 20 dizygotic co-twins without ADHD in childhood, and 20 unrelated controls selected from dizygotic twin pairs in which neither twin had ADHD in childhood (total n=60). Implicating the frontoparietal network as a location of effects specific to ADHD, activation in the superior frontal (Brodmann's Area - BA 6) and parietal regions (BA 40) was significantly reduced in twins with childhood ADHD compared to both their control co-twins and unrelated control twins. Consistent with familial influences, activity in the anterior cingulate and insula was significantly reduced in both the twins with ADHD and their co-twins compared to the unrelated controls. These results show that both ADHD-specific and familial influences related to an ADHD diagnosis impact neural systems underlying executive function., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Objectives: A twin-based comparative study on the genetic influences in metabolic endophenotypes in two populations of substantial ethnic, environmental, and cultural differences was performed., Design and Methods: Data on 11 metabolic phenotypes including anthropometric measures, blood glucose, and lipids levels as well as blood pressure were available from 756 pairs of Danish twins (309 monozygotic and 447 dizygotic twin pairs) with a mean age of 38 years (range: 18-67) and from 325 pairs of Chinese twins (183 monozygotic and 142 dizygotic twin pairs) with a mean age of 40.5 years (range: 18-69). Twin modeling was performed on full and nested models with the best fitting models selected., Results: Heritability estimates were compared between Danish and Chinese samples to identify differential genetic influences on each of the phenotypes. Except for hip circumference, all other body measures exhibited similar heritability patterns in the two samples with body weight showing only a slight difference. Higher genetic influences were estimated for fasting blood glucose level in Chinese twins, whereas the Danish twins showed more genetic regulation over most lipids phenotypes. Systolic blood pressure was more genetically controlled in Danish than in Chinese twins., Conclusions: Metabolic endophenotypes show disparity in their genetic determinants in populations under distinct environmental conditions., (Copyright © 2012 The Obesity Society.)

To understand a mechanism for the difference in clinical manifestations of congenital cytomegalovirus (CMV) infection between dizygotic twins, the placentas of the dizygotic twins were evaluated for the number of the cells infected with CMV by immunohistochemical and in situ hybridization studies. A Japanese woman with dizygotic twin pregnancy had immunoglobulin M antibodies to CMV at 15 weeks gestation. Intrauterine growth retardation was noted only in the first twin. At birth, CMV was isolated from urine culture in both twins. Clinical manifestations for CMV, such as petechiae, jaundice, hepatosplenomegaly, and deafness were more pronounced in the first twin than in the second twin. Immunohistochemical and in situ hybridization studies showed CMV-positive cells two or three times more densely distributed in the placenta of the first twin compared with the second twin. These data suggest the severity of CMV manifestations of dizygotic twins may be in accord with the number of CMV-positive cells in the placenta.