FG syndrome(FGS) is a genetic condition that affects many parts of the body and occurs almost exclusively in males. "FG" represents the surname initials of the first individuals diagnosed with the disorder. People with FG syndrome frequently have intellectual disability ranging from mild to severe, hypotonia, constipation and/or anal anomalies, a distinctive facial appearance, broad thumbs and great toes, a large head compared to body size (relative macrocephaly), and abnormalities of the corpus callosum. Medical problems including heart defects, seizures, undescended testicle, and an inguinal hernia have also been reported in some affected individuals. Researchers have identified five regions of the X chromosome that are linked to FG syndrome in affected families.Mutations in the MED12 gene appears to be the most common cause of this disorder, leading to FG syndrome 1. Other genes involved with FG syndrome include FLNA (FGS2), CASK (FGS4), UPF3B (FGS6), and BRWD3 (FGS7). FGS is inherited in an X-linked recessive pattern. Individualized early intervention and educational services are important so that each child can reach their fullest potential.

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Serious complications of FG syndrome, such as heart defects, breathing complications, or gastrointestinal (GI) malformations, may shorten the lifespan of affected individuals. Long-term survival has been reported, and several individuals with FG syndrome 1 have survived beyond age 50.