Developmental anomalies of the brain in mental retardation

Intuitively it is understood that persons with mental retardation must have 'something' different about the structure and organization of the central nervous system. In the past, defining what that something might be was usually a high cost, low yield endeavour. Recent advances in neuroimaging techniques have greatly enhanced our ability to identify structural changes in CNS development that correlate closely with the patient's neurodevelopmental abnormalities. In this article we review the most common identifiable developmental CNS anomalies seen in patients with mental retardation. We describe both overt (gross) malformations and the more recently appreciated 'subtle markers of cerebral dysgenesis: For selected conditions we also discuss recent insights into the etiologic and pathogenetic basis of the condition from many of the exciting new developments in molecular biology.