Differential Brain Development with Low and High IQ in Attention-Deficit/Hyperactivity Disorder

Attention-Deficit/Hyperactivity Disorder (ADHD) and intelligence (IQ) are both heritable phenotypes. Overlapping genetic effects have been suggested to influence both, with neuroimaging work suggesting similar overlap in terms of morphometric properties of the brain. Together, this evidence suggests that the brain changes characteristic of ADHD may vary as a function of IQ. This study investigated this hypothesis in a sample of 108 children with ADHD and 106 typically developing controls, who participated in a cross-sectional anatomical MRI study. A subgroup of 64 children also participated in a diffusion tensor imaging scan. Brain volumes, local cortical thickness and average cerebral white matter microstructure were analyzed in relation to diagnostic group and IQ. Dimensional analyses investigated possible group differences in the relationship between anatomical measures and IQ. Second, the groups were split into above and below median IQ subgroups to investigate possible differences in the trajectories of cortical development. Dimensionally, cerebral gray matter volume and cerebral white matter microstructure were positively associated with IQ for controls, but not for ADHD. In the analyses of the below and above median IQ subgroups, we found no differences from controls in cerebral gray matter volume in ADHD with below-median IQ, but a delay of cortical development in a number of regions, including prefrontal areas. Conversely, in ADHD with above-median IQ, there were significant reductions from controls in cerebral gray matter volume, but no local differences in the trajectories of cortical development

Reactive oxygen species, vascular disease, and hypertension

Reactive oxygen species (ROS) influence many physiological processes including host defense, hormone biosynthesis, fertilization, and cellular signaling. Increased ROS bioavailability and altered redox signaling (oxidative stress) have been implicated in chronic diseases including atherosclerosis and hypertension. Although oxidative injury may not be the sole etiology of hypertension, it amplifies blood pressure elevation in the presence of other pro-hypertensive factors, such as salt loading, activation of the renin-angiotensin system, and sympathetic hyperactivity. Oxidative stress is a multisystem phenomenon in hypertension and involves the heart, kidneys, nervous system, and vessels. A major source for cardiovascular, renal, and neural ROS is a family of non-phagocytic NADPH oxidases, including the prototypic Nox2 homologue-based NADPH oxidase, as well as other NADPH oxidases, such as Nox1 and Nox4. Other possible sources include mitochondrial electron transport enzymes, xanthine oxidase, cyclooxygenase, lipoxygenase, and uncoupled nitric oxide synthase (NOS). Cross talk between Noxes and mitochondrial oxidases is increasingly implicated in cellular ROS production. Convincing findings from experimental and animal studies support a causative role for oxidative stress in the pathogenesis of hypertension. However, there is still no solid evidence that oxidative stress is fundamentally involved in the pathogenesis of human hypertension. Reasons for this are complex and relate to heterogeneity of populations studied, inappropriate or insensitive methodologies to evaluate oxidative state clinically, and suboptimal antioxidant therapies used. Nevertheless, what is becoming increasingly evident is that oxidative stress is important in the molecular mechanisms associated with cardiovascular and renal injury in hypertension and that hypertension itself can contribute to oxidative stress. This chapter provides a comprehensive review of the role of ROS in the (patho)physiology of vascular injury and discusses the importance of Noxes in vascular oxidative stress. Implications in experimental and human hypertension are highlighted