FG syndrome

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FG syndrome
Classification and external resources
OMIM 305450
DiseasesDB 32162

FG syndrome (FGS; also known as Opitz–Kaveggia syndrome) is a rare genetic syndrome caused by one or more recessive genes located on the X chromosome and causing physical anomalies and developmental delays. First reported by Opitz and Kaveggia in 1974,[1] its major clinical features include intellectual disability, hyperactivity, hypotonia (low muscle tone), and a characteristic facial appearance including macrocephaly (an abnormally large head).[2]


FG syndrome's major clinical features include intellectual disability, usually severe; hyperactive behavior, often with an outgoing personality; severe constipation, with or without structural anomalies in the anus such as imperforate anus; macrocephaly; severe hypotonia; a characteristic facial appearance due to hypotonia, giving a droopy, "open-mouthed" expression, a thin upper lip, a full or pouting lower lip, and partial or complete loss of the corpus callosum. About a third of reported cases of individuals with FG syndrome die in infancy, usually due to respiratory infection; premature death is rare after infancy.[2]


Types include:

Type OMIM Gene Locus
FGS1 305450 MED12 Xq13
FGS2 300321 FLNA Xq28
FGS3 300406  ? Xp22.3
FGS4 300422 CASK Xp11.4-p11.3
FGS5 300581  ? Xq22.3


Kim Peek (1951–2009) probably had FG syndrome.

The name of the syndrome comes from the initials of the surnames of two sisters, who had five sons with the syndrome. The first study of the syndrome, published in 1974,[1] established that it was linked to inheritance of the X chromosome.[3]

A 2008 study concluded that Kim Peek, who was the basis for Dustin Hoffman's character Raymond Babbitt in the movie Rain Man, probably had FG syndrome[3] rather than autism.

See also[edit]


  1. ^ a b Opitz JM, Kaveggia EG (1974). "Studies of malformation syndromes of man XXXIII: the FG syndrome. An X-linked recessive syndrome of multiple congenital anomalies and mental retardation". Z Kinderheilkd. 117 (1): 1–18. doi:10.1007/BF00439020. PMID 4365204. 
  2. ^ a b Thompson E, Baraitser M (1987). "FG syndrome". J Med Genet. 24 (3): 139–43. doi:10.1136/jmg.24.3.139. PMC 1049945free to read. PMID 3572995. 
  3. ^ a b Opitz JM, Smith JF, Santoro L (2008). "The FG syndromes (Online Mendelian Inheritance in Man 305450): perspective in 2008". Adv Pediatr. 55: 123–70. doi:10.1016/j.yapd.2008.07.014. PMID 19048730.