FG syndrome: The trias mental retardation, hypotonia and constipation reviewed: A family with FG syndrome in two males and mild features in their mothers is reported. The data of the present family are compared with the 56 patients from the literature. At birth, affected individuals present with hypotonia and constipation and/or anal anomalies and joint hyperlaxity. Mental deficiency is the rule. Craniofacial dysmorphism is nonspecific. Macrocephaly may be present at birth or develop later in life. Features in older patients include joint contractures and a typical pleasant personality, sometimes with sudden aggressive outbursts. FG syndrome has a variable clinical presentation and clinical diagnosis is difficult, especially in sporadic patients. A thorough family examination with special attention to mild symptoms in female relatives is emphazised.