The prevalence of a range of DSM-IV psychiatric disorders in a sample of 119 4 -16-year-old children with Williams syndrome (WS) was assessed using a structured diagnostic interview with their parents. Most children (80.7%) met criterion for at least one DSM-IV diagnosis. The most prevalent diagnoses were attention deficit/hyperactivity disorder (ADHD; 64.7%) and specific phobia (53.8%). There was a significant shift in predominant type of ADHD as a function of CA, from Combined for the youngest group (ages 4 -6 years) to Inattentive for the oldest group (ages 11 -16 years). The prevalence of generalized anxiety disorder (GAD) increased significantly with age. These findings are another step toward defining the behavioral phenotype of WS.

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Group-matching designs are commonly used to identify the diagnosis-specific characteristics of children with developmental disabilities. In this paper, we address three issues central to the use of this design. The first concerns the alpha level to be used for considering groups to be matched on the control variable(s). The second involves the measurement characteristics of the control and target variables. We discuss the properties of standard scores, raw scores, and age equivalents and argue against the use of age equivalents. In addition, we consider the appropriateness of the commonly made prediction that groups that are matched for a control variable such as language ability or nonverbal reasoning ability but are not matched for chronological age should perform at equivalent levels on the target variable. Finally, we discuss issues related to the interpretation of significant between-group differences on the target variable, assuming groups are well-matched on the control variables, and describe the benefits of a method that focuses on characterizing a disorder on a case-by-case basis and then aggregating the cases, using the measures of sensitivity and specificity from signal detection theory.

Two studies were conducted to consider the looking behavior of infants and toddlers with Williams syndrome (WS). In Study 1,the looking behavior of a 10-month-old girl with WS during play sessions with her mother and with a stranger was compared to that of 2 groups of infants who were developing normally (ND),1 matched for chronological age and the other for developmental age. The infant with WS spent more than twice as much time looking at her mother as the infants in either contrast group did. She also spent twice as much time looking at the stranger. In addition, during 78%of this time, her gaze at the stranger was coded as extremely intense. Looks of this intensity were virtually never made by the ND infants. In Study 2,the looking behavior of 31 individuals with WS ages 8 to 43 months during a genetics evaluation was compared to that of 319 control children in the same age range (242 with developmental delay due to causes other than WS).Twenty-three of the 25 participants with WS aged 33 months or younger demonstrated extended and intense looking at the geneticist. In contrast, none of the control participants looked extensively or intently at the geneticist. Findings are discussed in the context of previous research on arousal and focused attention during normal development and on temperament and personality of older children and adults with WS. It is argued that the unusual looking patterns evidenced by infants and toddlers with WS presage the unusual temperament and personality of older individuals with WS, and the possibility of a genetic basis for these behaviors is addressed.

Williams syndrome is caused by a microdeletion of at least 16 genes on chromosome 7q11.23. The syndrome results in mild to moderate mental retardation or learning disability. The behavioral phenotype for Williams syndrome is characterized by a distinctive cognitive profile and an unusual personality profile. Relative to overall level of intellectual ability, individuals with Williams syndrome typically show a clear strength in auditory rote memory, a strength in language, and an extreme weakness in visuospatial construction. The personality of individuals with Williams syndrome involves high sociability, overfriendliness, and empathy, with an undercurrent of anxiety related to social situations. The adaptive behavior profile for Williams syndrome involves clear strength in socialization skills (especially interpersonal skills related to initiating social interaction), strength in communication, and clear weakness in daily living skills and motor skills, relative to overall level of adaptive behavior functioning. Literature relevant to each of the components of the Williams syndrome behavioral phenotype is reviewed, including operationalizations of the Williams syndrome cognitive profile and the Williams syndrome personality profile. The sensitivity and specificity of these profiles for Williams syndrome, relative to individuals with other syndromes or mental retardation or borderline normal intelligence of unknown etiology, is considered. The adaptive behavior profile is discussed in relation to the cognitive and personality profiles. The importance of operationalizations of crucial components of the behavioral phenotype for the study of genotype/phenotype correlations in Williams syndrome is stressed. MRDD Research Reviews 2000;6:148‐158. © 2000 Wiley‐Liss, Inc.