ABSTRACT
University of Texas Health Science Center at San Antonio, San Antonio, Texas, U.S.A.
I. INTRODUCTION
Most neurodevelopmental disorders are recognized either by their phenotype (physical appearance) and/or by their genotype (chromosomal and/or molecular appearance). Unfortunately, there is neither a specific phenotype nor a consistent genotype that reliably defines autism spectrum disorder (ASD). Relatively new to the field of neurodevelopmental disorders is the recognition of “behavioral” phenotypes. Although the characteristic behaviors of some “syndromes” have been recognized for quite some time, it has only been in the recent past that sophisticated genetic diagnostic techniques [e.g., fluorescent in situ hybridization (FISH)] have provided the corresponding genetic characteristics allowing the two to be reliably linked to one another. Examples of such behavioral phenotypes (and their corresponding genotype) include, but are not limited to: hand-wringing and hyperventilation characteristic of Rett’s syndrome (MECP2), selfhugging in Smith-Magenis (17p11.2 deletion), excessive smiling and wide-based puppetlike gait in Angelman’s syndrome (15 q11-13 deletion of maternal origin), extreme hyperphagia in Prader-Willi syndrome (15 q11-13 deletion of paternal origin), 5 and selfbiting and tissue destruction of lips and hands in Lesch-Nyhan (X q26-27).
