Two unrelated males with mental retardation (Figure 1 and Figure 2). Southern blot patterns of DNA from family members of a child with mental retardation (Figure 3).
Denouement and Discussion
Fragile X Syndrome
Fragile X syndrome is the most common familial form of mental retardation known. The incidence is one in 1000 to 1500 males in the general population and one case of a generally milder mental handicap in every 2000 to 2500 females. The syndrome typically presents with the combination of mental retardation with developmental and speech delay, abnormal facial features, and macroorchidism. Behavioral abnormalities are common, including hyperactivity, short attention span, hand flapping movement disorders, poor eye contact, and poor gross motor coordination, features that often suggest autism. A mild connective tissue dysplasia may be associated with this syndrome as evidenced by the presence of hyperextensibility of the joints, pes planus, mitral valve prolapse, or mild aortic