BIOLOGICAL CORRELATES OF ATTENTION-DEFICIT HYPERACTIVITY DISORDER (ADHD)

This paper reviews the literature available in relation to biological basis of attention deficit-hyperactivity disorder (ADHD). Twin, adopti on, family-genetic and segregation analysis studies have emphasized th e existence of an important genetic contribution to the etiology of AD HD. Overall, data are concordant with the notion of a poligenetic inhe ritance. On the other hand, from a neurochemical point of view, severa l neurotransmitters have been involved in the genesis of this disorder . The fact that stimulant drugs act as dopaminergic and noradrenergic agonists has lead to the ''catecholamines hypothesis''. However, no co mprehensive model has been proposed which successfully describes the u nderlying pathophysiology of ADHD and the mechanisms by which psychost imulants ameliorate the symptomatology. Likewise, we examine several n euroendocrinological investigations which have demonstrated a dysfunct ion of thyroid system in the ADHD as well as the main studies using st ructural and functional neuroimaging techniques which have showed a cl ear fronto-striatal-cortical dysfunction in these patients. Finally, w e describe some recent neuroimmunological studies which indicate that C4B levels may be an important marker for ADHD.