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Handedness has been extensively studied because of its relationship with language and the over-representation of left-handers in some neurodevelopmental disorders. Using data from the UK Biobank, 23andMe and the International Handedness Consortium, we conducted a genome-wide association meta-analysis of handedness (N = 1,766,671). We found 41 loci associated (P

Individuals with dyslexia are at an increased risk for anxiety disorders (e.g. generalized anxiety disorder, stress disorders, panic disorder). The extent to which this association is mediated by genetic and/or environmental influences is unclear. The current study explored the relationship between these two phenotypes using a large population-based twin sample. In total, 940 monozygotic and 903 dizygotic female twin pairs were included in the analyses. The presence of dyslexia and anxiety was determined by self-report of diagnosis by a health professional. Tetrachoric correlations confirmed an association between the two phenotypes, but suggested that there was no evidence for shared genetic risks. Bivariate twin modelling corroborated this finding and indicated the relationship between dyslexia and anxiety is mediated by shared environmental factors. Future research should seek to identifying the environmental factors that increase the vulnerability of individuals with dyslexia to emotional problems should be a priority for future research. (Contains 2 figures and 3 tables.)

The genetic relationship between intelligence and components of cognition remains controversial. Conflicting results may be a function of the limited number of methods used in experimental evaluation. The current study is the first to use CANTAB (The Cambridge Neuropsychological Test Automated Battery). This is a battery of validated computerised cognitive tests, which allows assessment across a number of domains. A sample of 278 female-female Caucasian twin pairs from the UK (aged 18-76) performed such tests to establish the importance of genetic factors on four composite cognitive measures: general memory ability, inspection time (IT), working memory, and reaction time (RT). Estimates of heritability (additive genetic variance) were found to be 57% (95% CI 44, 68) for general memory, 38% (23, 51) for IT and 31% (16, 45) for working memory. The National Adult Reading Test (NART), a measure of IQ, had a heritability of 76%. RT was explained by common environmental influences and nonshared environmental influences. Moderate phenotypic correlations between general memory and NART (r = 0.32) and general memory and working memory (r = 0.42) were also reported. Both relationships could be explained by shared genetic determinants.

A research was conducted on 278 female-female Caucasian twin pairs from the UK to find the significance of genetic factors on four composite cognitive components like general memory ability, inspection time (IT), working memory, and reaction time (RT). The computerized cognitive testing for genetic studies on application showed the heritabilities range for the composite scores and also highlighted the use of battery to assess the general cognitive functioning and its relationship with specific cognitive abilities.

Abstract Background Certain conditions characterised by blood vessel occlusion or vascular spasm have been found to cluster together in epidemiological studies. However the biological causes for these associations remain controversial. This study used a classical twin design to examine whether these conditions are linked through shared environmental exposures or by a common underlying genetic propensity to vasospasm. Methods We investigated the association between hypertension, migraine, Raynaud's phenomenon and coronary artery disease in twins from a national register. Phenotype status was determined using a questionnaire and the genetic and environmental association between phenotypes was estimated through variance components analysis. Results Responses were obtained from 2,204 individuals comprising 525 monozygotic and 577 dizygotic pairs. There was a significant genetic contribution to all four traits with heritabilities ranging from 0.34 to 0.64. Multivariate model-fitting demonstrated that a single common genetic factor underlies the four conditions. Conclusions We have confirmed an association between hypertension, migraine, Raynaud's phenomenon and coronary artery disease, and shown that a single genetic factor underlies them. The demonstration of a shared genetic factor explains the association between them and adds weight to the theory of an inherited predisposition to vasospasm.

Background: Motion sickness is a common and potentially debilitating condition that characteristically occurs in situations of conflicting sensory input. While the precise stimuli that give rise to this trait are increasingly well characterized, the underlying determinants of individual susceptibility to motion sickness remain unclear. This study uses a classical twin design to assess the influence of genetic and environmental factors., Methods: A postal survey was conducted in an age-matched sample of 3652 monozygotic (MZ) and dizygotic (DZ) adult female twins selected from the TwinsUK Registry. Study participants were asked to complete items from a validated questionnaire relating to their lifetime susceptibility to motion sickness. The relative contribution of genetic and environmental factors to motion sickness susceptibility was assessed using variance components analysis., Results: The response rate to the questionnaire was 78%. Approximately 40% of respondents reported at least moderate susceptibility to motion sickness. The pattern of responses among twins indicated a significant genetic contribution with heritability for a motion sickness factor score estimated as 57% (95% CI: 51%, 63%). The heritability of recalled motion sickness was at its highest in childhood (70% [59%, 80%]) and declined through puberty and the early adult years., Discussion and Conclusions: The findings highlight the importance of genetic factors in determining an individual's underlying propensity to motion sickness and should stimulate the search for specific susceptibility genes.

Sleep disorders, such as obstructive sleep apnoea (OSA) and restless legs syndrome (RLS), are very common. The relative importance of genetic and nongenetic (environmental) influences on the symptomatology of these conditions has not been well studied. This study uses the twin design to examine this by evaluating OSA and RLS symptoms in monozygotic (MZ) and dizygotic (DZ) twins. Six thousand six hundred unselected female twin pairs, identified from a national volunteer twin register, were asked to complete a medical questionnaire. This questionnaire included questions on OSA and RLS symptoms, as well as questions on subject demographics, past medical history, smoking history and menopausal status. Responses were obtained from 4503 individuals (68% response rate). A total of 1937 twin pairs were evaluable: 933 MZ pairs (mean [range] age 51 [20-76] years) and 1004 DZ pairs (age 51 [20-80] years). Concordance rates were higher for MZ than DZ twins for OSA and RLS symptoms. Multifactorial liability threshold modeling suggests that additive genetic effects combined with unique environmental factors provide the best model for OSA and RLS symptoms. Heritability was estimated to be 52% (95% confidence interval 36% to 68%) for disruptive snoring, 48% (37% to 58%) for daytime sleepiness, 54% (44% to 63%) for restless legs, and 60% (51% to 69%) for legs jerking. These estimates dropped only slightly after adjustment for potential confounding influences on the symptoms of snoring and daytime sleepiness. These results suggest a substantial genetic contribution to the symptomatology of OSA and RLS. More research is needed to identify the genes responsible, and may ultimately lead to new therapies.