ABSTRACT
Genetic factors play an important etiologic role for many forms of mental retardation. A recent paper detailing the gene map of mental retardation (Wahlstrom, 1990) found mental retardation to be involved in 503 diseases, for which 69 were mapped to an autosome, 73 to the X-chromosome and more than 300 were identified as having a genetic origin with unknown location. Two genetic disorders, Down syndrome and fragile X syndrome, will typically account for one third of the identified genetic cases in samples of individuals affected by mental retardation (Bregman & Hodapp, 1991).
