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MZ Twin Pairs (mz + twin_pair)
Selected AbstractsGene expression analysis in absence epilepsy using a monozygotic twin designEPILEPSIA, Issue 9 2008Ingo Helbig Summary Purpose: To identify genes involved in idiopathic absence epilepsies by analyzing gene expression using a monozygotic (MZ) twin design. Methods: Genome-wide gene expression in lymphoblastoid cell lines (LCLs) was determined using microarrays derived from five discordant and four concordant MZ twin pairs with idiopathic absence epilepsies and five unaffected MZ twin pairs. Gene expression was analyzed using three strategies: discordant MZ twins were compared as matched pairs, MZ twins concordant for epilepsy were compared to control MZ twins, and a singleton design of affected versus unaffected MZ twin individuals was used irrespective of twin pairing. An overlapping gene list was generated from these analyses. Dysregulation of genes recognized from the microarray experiment was validated using quantitative real time PCR (qRT-PCR) in the twin sample and in an independent sample of 18 sporadic absence cases and 24 healthy controls. Results: Sixty-five probe sets were identified from the three combined microarray analysis strategies. Sixteen genes were chosen for validation and nine of these genes confirmed by qRT-PCR in the twin sample. Differential expression for EGR1 (an immediate early gene) and RCN2 (coding for the calcium-binding protein Reticulocalbin 2) were reconfirmed by qRT-PCR in the independent sample. Discussion: Using a unique sample of discordant MZ twins, our study identified genes with altered expression, which suggests novel mechanisms in idiopathic absence epilepsy. Dysregulation of EGR1 and RCN2 is implicated in idiopathic absence epilepsy. [source] Long-Term Leisure Time Physical Activity and Properties of Bone: A Twin Study,,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 8 2009Hongqiang Ma Abstract Effects of physical activity on bone properties, when controlled for genetic effects, are not fully understood. We aimed to study the association between long-term leisure time physical activity (LTPA) and bone properties using twin pairs known to be discordant for leisure time physical activity for at least 30 yr. Volumetric BMD and geometric properties were measured at the tibia shaft and distal end using pQCT in 16 middle-aged (50,74 yr) same-sex twin pairs (seven monozygotic [MZ] and nine dizygotic [DZ] pairs) selected from a population-based cohort. Paired differences between active and inactive co-twins were studied. Active members of MZ twin pairs had larger cortical bone cross-sectional area (intrapair difference: 8%, p = 0.006), thicker cortex (12%, p = 0.003), and greater moment of inertia (Imax, 20%, p = 0.024) at the tibia shaft than their inactive co-twins. At the distal tibia, trabecular BMD (12%, p = 0.050) and compressive strength index (18%, p = 0.038) were also higher in physically active MZ pair members than their inactive co-twins. The trends were similar, but less consistently so, in DZ pairs as in MZ pairs. Our genetically controlled study design shows that LTPA during adulthood strengthens bones in a site-specific manner, that is, the long bone shaft has a thicker cortex, and thus higher bending strength, whereas the distal bone has higher trabecular density and compressive strength. These results suggest that LTPA has a potential causal role in decreasing the long-term risk of osteoporosis and thus preventing osteoporotic fractures. [source] Genetic Contribution to Bone Metabolism, Calcium Excretion, and Vitamin D and Parathyroid Hormone RegulationJOURNAL OF BONE AND MINERAL RESEARCH, Issue 2 2001D. Hunter Abstract A classical twin study was performed to assess the relative contribution of genetic and environmental factors to bone metabolism, calcium homeostasis, and the hormones regulating them. It was examined further whether the genetic effect is menopause dependent. The subjects were 2136 adult twins (98.3% female): 384 monozygotic (MZ) and 684 dizygotic (DZ) twin pairs. The intraclass correlations were calculated, and maximum likelihood model fitting was used to estimate genetic and environmental variance components. The intraclass correlations for all of the variables assessed were higher in MZ twin pairs. The heritabilities (95% CIs) obtained from model fitting for hormones regulating bone metabolism and calcium homeostasis were parathyroid hormone (PTH), 60% (54,65%); 25-hydroxyvitamin D [25(OH)D]; 43% (28,57%), 1,25-hydroxyvitamin D [1,25(OH)], 65% (53,74%); and vitamin D binding protein 62% (56,66%). The heritabilities (95% CIs) for markers of bone formation also were assessed; bone-specific alkaline phosphatase (BSAP), 74% (67,80%), and osteocalcin, 29% (14,44%); marker of bone resorption deoxypyridinoline (DPD), 58% (52,64%); and measure of calcium homeostasis 24 h urine calcium, creatinine (Cr), 52% (41,61%). The magnitude of genetic influence differed with menopause for most variables. This study provides evidence for the importance of genetic factors in determining bone resorption and formation, calcium excretion, and the hormones regulating these processes. It shows for the first time a clear genetic effect on bone resorption in premenopausal women and the regulation of PTH, vitamin D metabolism, and calcium excretion. The genes controlling bone hormones and markers are likely to be useful therapeutic and diagnostic targets. [source] Non-identical monozygotic twins, intermediate twin types, zygosity testing, and the non-random nature of monozygotic twinning: A review,AMERICAN JOURNAL OF MEDICAL GENETICS, Issue 2 2009Geoffrey Machin Abstract Monozygotic twins (MZ) are rarely absolutely "identical." This review discusses the types of genetic/epigenetic and prenatal environmental post-zygotic mechanisms that cause discordance within such twin pairs. Some of these mechanisms,ranging from heterokaryotypia to skewed X-chromosome inactivation,may cause extreme discordance, but these extremes are merely the more emphatic examples of discordance that, to some degree, underlies the majority of MZ twin pairs. Because of the entrenched misconception that MZ twins are necessarily identical, many MZ twin pairs are mistakenly designated as dizygotic (DZ). Clinical benefits to accurate zygosity determination include correct solid organ transplantation matching, if one twin requires donation for a non-genetically mediated disease; the opportunity of preventive management for disorders that do not manifest synchronously; and better counseling to parents regarding their individually unique, and often psychologically puzzling, twin offspring. In twin pairs with complex and confusing biological origins, more detailed zygosity testing may be required. For example, intermediate trigametic and tetragametic chimeric dizygotic twins are reviewed, some of whom are, nevertheless, monochorionic (MC). Because of inter-fetal vascular anastomoses in MC twins, genetic results from blood samples may not accurately reflect discordance in solid organs. Previously, it was thought that MZ twinning was some sort of embryological fluke. However, familial monozygotic twinning is more common than suggested by the literature. Seven new families are presented in an accompanying paper. Despite the difficulties and dangers of twin pregnancy (especially so for MC twins), human twinning persists, and continues to both challenge and fascinate parents, clinicians and geneticists. © 2009 Wiley-Liss, Inc. [source] Familial monozygotic twinning: A report of seven pedigrees,AMERICAN JOURNAL OF MEDICAL GENETICS, Issue 2 2009Geoffrey Machin Abstract Seven families contained 19 MZ twin pairs (2.7 pairs/family), diagnosed by low-stringency variable number tandem repeats in DNA from placental tissue or blood. Chorion status was known in 10 pairs, 6 dichorionic, 4 monochorionic. Sex ratio was equal. Autosomal dominant inheritance is apparent. © 2009 Wiley-Liss, Inc. [source] Genetic and environmental influence on language impairment in 4-year-old same-sex and opposite-sex twinsTHE JOURNAL OF CHILD PSYCHOLOGY AND PSYCHIATRY AND ALLIED DISCIPLINES, Issue 2 2004Essi Viding Background:, We investigated the aetiology of language impairment in 579 four-year-old twins with low language performance and their co-twins, members of 160 MZ twin pairs, 131 same-sex DZ pairs and 102 opposite-sex DZ pairs. Methods:, Language impairment in 4-year-olds was defined by scores below the 15th percentile on a general factor derived from an extensive language test battery. Language impairment of different degrees of severity was investigated by using multiple cut-offs below the 15th percentile. Results:, DeFries,Fulker extremes analysis indicated that language impairment as measured by the general language scale is under strong genetic influence. In addition, group differences heritability showed an increasing trend (from 38% to 76%) as a function of severity of language impairment. Although more boys are impaired than girls, incorporating opposite-sex DZ pairs into the analysis found neither quantitative nor qualitative differences between boys and girls in genetic and environmental aetiologies. Conclusions:, Language impairment at four years is heritable. This finding replicates previous research on language impairment and extends it by showing that language impairment is heritable in twins selected from a representative community sample. Despite the mean difference between boys and girls, genetic and environmental influences are quantitatively and qualitatively similar for language impairment for boys and girls. For both boys and girls, heritability appears to be greater for more severe language impairment, indicating stronger influence of genes at the lower end of language ability. [source] Prevalence and side preference for tooth grinding in twinsAUSTRALIAN DENTAL JOURNAL, Issue 3 2006KV Dooland Abstract Background: Estimates of the prevalence of tooth grinding in children range considerably, reflecting different methods of recording. The main aims of this study were to determine the prevalence of tooth grinding in monozygotic (MZ) and dizygotic (DZ) twin pairs by assessing wear faceting on the primary canines, and to compare the faceting on the right and left to determine whether children have a side preference for grinding. Methods: The sample consisted of 116 MZ twin pairs and 124 dizygous DZ twin pairs, all participants in an ongoing study of dento-facial development at the dental schools in Adelaide and Melbourne. Evidence of wear faceting on primary maxillary and mandibular canine tips was recorded from dental casts, and the side with the larger wear facet recorded. Types of occlusal relationship, handedness, zygosity and gender were also recorded, and associations between variables analysed statistically. Results: Canine tip wear facets were found in 100 per cent of the sample, and grinding was lateralized in 59 per cent of children. MZ twin pairs showed a higher discordance for grinding side preference than DZ twin pairs (33.8 per cent compared with 16.8 per cent), providing evidence of a mirror-imaging effect for grinding side preference. There was no strong evidence that individuals had the same preference for grinding side and handedness, although right-handers (RH) showed a preference for a grinding side more often than non-righthanders (NRH) (63.6 per cent compared with 51.2 per cent), consistent with previous findings that RHs display more cerebral lateralization than NRHs. Conclusions: Tooth grinding appears to be a universal phenomenon in children and is commonly expressed more on one side than the other. The significantly higher discordance for grinding side preference in MZ twin pairs compared with DZ twin pairs may reflect a mirror-imaging effect in the former. However, at present we have no evidence to suggest that handedness and preferred tooth grinding side are associated. [source] | ||||||||||