ABSTRACT
Introduction and terminology This chapter provides an introduction to the concept of syndromes and describes some genetically determined syndromes that are or may be associated with learning disability. Some basic genetic terms and concepts are discussed in Chapter 2. Terms that are used to describe how common diseases are include incidence and prevalence. The incidence of a disease is the rate of occurrence of new cases in a defined population over a given period of time. Prevalence is the proportion of a defined population that has a disease at a given point in time or over a given period of time.
