Neuroanatomical Distinctions Between Williams and Down Syndromes
Terry L. Jernigan Veterans Affairs Medical Center and University of California, San Diego
Ursula Bellugi The Salk Institute for Biological Studies
Williams syndrome (WS) is a rare developmental disorder characterized by mental retardation ( Jones & Smith, 1975; Preus, 1984; von Arnim & Engel, 1964; Williams, Barrett-Boyes, & Lowe, 1961). Several reports have appeared describing some of the neuropsychological deficits observed in WS subjects ( Crisco, Dobbs, & Mulhern, 1988; MacDonald & Roy, 1988; Udwin & Yule, 1991). Although these studies present conflicting results, most note their particularly poor visuospatial and visuomotor abilities. These studies have generally contrasted the performance of WS subjects on standardized tests to those of normal children or IQ-matched controls with mixed or nonspecific developmental disorders. In a series of recent neurobehavioral investigations, the unusual profile of higher cognitive functions in WS subjects has been illuminated ( Bellugi, Bihrle, Jernigan, Trauner, & Doherty, 1990; Bellugi, Bihrle, Neville, Jernigan, & Doherty, 1992; Bellugi, Sabo, & Vaid, 1988; see also chapter 2 of this volume).
Studies under the Neurodevelopmental Research Center focus on carefully selected WS children who have been clearly diagnosed as WS by genetic or metabolic markers, who are all in a similar age range (10 years and above), and who are contrasted with another well-defined genetically based disorder of mental retardation, Down syndrome (DS). The two groups are matched in age, gender, educational background, and IQ. Both groups of subjects undergo magnetic resonance imaging (MRI), neurological exams, and a