The neuronal group selection theory: promising principles for understanding and treating developmental motor disorders.

Abstract

There are two major forms of developmental motor disorders: cerebral palsy (CP) and clumsiness. CP is an umbrella term covering a group of non-progressive, but often changing, motor impairment syndromes secondary to lesions or anomalies of the brain arising in the early stages of development. It affects about 1 in 500 live-born children. Clumsy children nowadays are classified according to DSM-IV as having developmental coordination disorder (DCD), a term denoting children who have such poor motor coordination that it affects daily activities at home and at school, but with normal intelligence and without obvious neurological pathology. The prevalence of DCD is about 10% (6 to 13%). The understanding of the motor problems in both groups of children is hampered by the large heterogeneity within each group. In both groups children differ in the expression of their motor dysfunction, in comorbidity such as the presence of cognitive and behavioural disorders, and in aetiology. In addition, the relation between the various motor disorders and the structural abnormalities of the brain is far from simple. CP is, by definition, attributed to lesions or anomalies of the young brain, but the abnormalities of the brain cannot always be visualized with imaging techniques. Despite there being some relation between lesions of the periventricular white matter and spastic diplegia, and between unilateral lesions and spastic hemiplegia, the site of the lesion does not correlate exactly with the type of motor dysfunction. In children with DCD the connection between structural abnormalities of the brain and motor dysfunction is still more ambiguous. Recently Hadders-Algra and Touwen argued that indications for pre- and perinatal brain damage can be found only in one third of children with minor motor dysfunction. This could imply that most clumsy children do not have macroscopic anomalies of the brain, but dysfunctions at the microscopic level of the nervous system, with abnormalities in the neurotransmitter or receptor systems, for example.