Behavioral phenotypes in genetic syndromes: genetic clues to human behavior.

A behavioral phenotype is the characteristic cognitive, personality, behavioral, and psychiatric pattern that typifies a disorder. A number of genetic syndromes have been identified as having this type of distinctive and consistent behavior pattern. It may act as an important diagnostic sign, like a malformation or characteristic facial appearance. Such patterns are also useful for the physician's anticipatory guidance from an educational, rehabilitative, and parenting perspective. In addition, because they are the consequences of known genetic alterations, behavioral phenotypes can be potentially highly valuable clues to the identification of genes in the population that are important to determination of cognitive skills or deficits, personality determinants, behavioral abnormalities, or psychiatric disorders. The nature of a behavioral phenotype and its potential for genetic insight can be appreciated through the examples of Williams syndrome, Prader-Willi syndrome, and Angelman syndrome. The cognitive and behavioral characteristics of these disorders are distinctive. Williams syndrome is known for its association with remarkable conversational verbal abilities and excessive empathy, whereas Prader-Willi syndrome is known for temper tantrums and obsessive-compulsive features, and Angelman syndrome is associated with a constantly happy affect and hyperactivity. The genetic basis for each of these disorders is known, and the pathophysiology and genotype-phenotype correlations are beginning to provide insight into genes responsible for personality characteristics and behavioral abnormalities.