FG syndrome
Encyclopedia
FG syndrome is a rare genetic syndrome linked to the X chromosome
and causing physical anomalies and developmental delays. First reported by Opitz and Kaveggia in 1974, its major clinical features include retardation
, hyperactivity, hypotonia
(low muscle tone), and a characteristic facial appearance including macrocephaly
(an abnormally large head).
; 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.
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, established that it was linked to inheritance of the X chromosome
.
A 2008 study concluded that Kim Peek
, who was the basis for the Dustin Hoffman
character in the movie Rain Man
, probably had FG syndrome.
X chromosome
The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals and is common in both males and females. It is a part of the XY sex-determination system and X0 sex-determination system...
and causing physical anomalies and developmental delays. First reported by Opitz and Kaveggia in 1974, its major clinical features include retardation
Mental retardation
Mental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...
, hyperactivity, hypotonia
Hypotonia
Hypotonia is a state of low muscle tone , often involving reduced muscle strength. Hypotonia is not a specific medical disorder, but a potential manifestation of many different diseases and disorders that affect motor nerve control by the brain or muscle strength...
(low muscle tone), and a characteristic facial appearance including macrocephaly
Macrocephaly
Macrocephaly , occurs when the head is abnormally large; this includes the scalp, the cranial bone, and the contents of the cranium.-Causes:...
(an abnormally large head).
Characteristics
FG syndrome's major clinical features include mental retardation, usually severe; hyperactive behavior, often with an outgoing personality; severe constipation, with or without structural anomalies in the anus such as imperforate anusImperforate anus
An imperforate anus or anal atresia is a birth defect in which the rectum is malformed. Its cause is unknown.-Features:There are several forms of imperforate anus:* A low lesion, in which the colon remains close to the skin...
; macrocephaly
Macrocephaly
Macrocephaly , occurs when the head is abnormally large; this includes the scalp, the cranial bone, and the contents of the cranium.-Causes:...
; 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
Corpus callosum
The corpus callosum , also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication...
. 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.
Genetics
Types include:| Type | OMIM | Gene | Locus |
|---|---|---|---|
| FGS1 | MED12 MED12 Mediator of RNA polymerase II transcription, subunit 12 homolog , also known as MED12, is a human gene found on the X chromosome... |
Xq13 | |
| FGS2 | FLNA FLNA Filamin-A is a protein that in humans is encoded by the FLNA gene.- Function :Actin-binding protein, or filamin, is a 280-kD protein that crosslinks actin filaments into orthogonal networks in cortical cytoplasm and participates in the anchoring of membrane proteins for the actin cytoskeleton.... |
Xq28 | |
| FGS3 | ? | Xp22.3 | |
| FGS4 | CASK CASK Peripheral plasma membrane protein CASK is a protein that in humans is encoded by the CASK gene. This gene is also known by several other names: CMG 2 , calcium/calmodulin-dependent serine protein kinase 3 and membrane-associated guanylate kinase 2.-Genomics:This gene is located on the short arm of... |
Xp11.4-p11.3 | |
| FGS5 | ? | Xq22.3 |
History
X chromosome
The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals and is common in both males and females. It is a part of the XY sex-determination system and X0 sex-determination system...
.
A 2008 study concluded that Kim Peek
Kim Peek
Laurence Kim Peek was an American savant. Known as a "megasavant", he had a photographic or eidetic memory, but also social difficulties, possibly resulting from a developmental disability related to congenital brain abnormalities. He was the inspiration for the character of Raymond Babbitt,...
, who was the basis for the Dustin Hoffman
Dustin Hoffman
Dustin Lee Hoffman is an American actor with a career in film, television, and theatre since 1960. He has been known for his versatile portrayals of antiheroes and vulnerable characters....
character in the movie Rain Man
Rain Man
Rain Man is a 1988 drama film written by Barry Morrow and Ronald Bass and directed by Barry Levinson. It tells the story of an abrasive and selfish yuppie, Charlie Babbitt, who discovers that his estranged father has died and bequeathed all of his multimillion-dollar estate to his other son,...
, probably had FG syndrome.