Introduction

A major challenge in both clinical practice and research in the field of intellectual disabilities and of learning disorders is to identify the underlying causes: the genetic, chromosomal, and environmental factors that have important influences on a person's development and behavior. Advances in clinical genetics have led to an increased recognition of specific syndromes. In recent years, cytogenetic and molecular genetic tools have resulted in the identification of the underlying genetic defects in a large number of disorders e.g., the 22q11.2 microdeletion in velo-cardio-facial syndrome (VCFS).

For many years, interest was focused on the delineation of the somatic aspects of the phenotypes and their underlying pathogenetic mechanisms. However, in the last decade, researchers have paid more attention to the cognitive and behavioral features of various genetic conditions, the so-called “behavioral phenotype.” A behavioral phenotype is broadly defined as “a behavioural pattern, including cognitive processes and social interaction style, consistently associated with, and specific to, a syndrome with a chromosomal or a genetic aetiology” (Flint, 1996). This definition does not propose a simple, one-to-one or universal relationship link between the behavioral phenotype and the associated biological/genetic disorder. On the contrary, the relationships are complex and varied.

It was not until 1992 that submicroscopic deletions on chromosome 22q11 were identified, confirming that VCFS is indeed a specific syndrome (Scambler et al., 1991; Driscoll et al., 1992).