Rational evaluation of the adolescent with mental retardation.

Mental retardation in adolescents presents multiple challenges. Among these is the frequent lack of an accurate etiologic diagnosis. Retarded youngsters may enter adolescence without an established diagnosis; in many, no attempt at diagnosis has been made. The diagnostic approach is often more difficult in adolescents than in younger children because of the effects of age on physical features and changes in the family structure. Despite these challenges, advances in cytogenetic technology, cranial imaging, and molecular diagnostics offer patients and families real hope that a diagnosis can be achieved, even when previous attempts have failed. This chapter discusses the benefits and yield of such evaluations. The appropriate clinical and laboratory diagnostic evaluations are discussed with attention to the indications for chromosomal analyses, molecular testing, cranial imaging, and targeted metabolic testing.