FG syndrome

FG syndrome
Kim Peek (1951–2009) probably had FG syndrome
OMIM	305450
DiseasesDB	32162

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Kalsang Dolma, M.B.B.S.[2]

Synonyms and keywords: Opitz-Kaveggia syndrome; Keller syndrome; FGS; FGS1; mental retardation, large head, imperforate anus; congenital hypotonia, and partial agenesis of the corpus callosum; OKS

Overview

FG syndrome is a rare genetic syndrome linked to the X chromosome and causing physical anomalies and developmental delays.

Historical Perspective

First reported by Opitz and Kaveggia in 1974, 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.

Pathophysiology

Genetics

• Researchers have identified five regions of the X chromosome that are linked to FG syndrome in affected families. In one of these regions, a mutation in a particular gene called MED12 has been found to cause the disorder. Researchers are investigating genes in other regions of the X chromosome that may also be associated with FG syndrome.
• The MED12 gene provides instructions for making a protein that helps regulate gene activity. Specifically, the MED12 protein forms part of a large complex (a group of proteins that work together) that turns genes on and off. The MED12 protein is thought to play an essential role in development both before and after birth.
• Researchers have identified one mutation in the MED12 gene in several people with FG syndrome. Although the mutation alters the structure of the MED12 protein, it is unclear how this change leads to intellectual disability, behavioral changes, and the physical features associated with this condition.

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

Epidemiology and Demographics

The prevalence of FG syndrome is unknown, although several hundred cases have been reported worldwide. Researchers suspect that FG syndrome may be over diagnosed because many of its signs and symptoms are also seen with other disorders.

Natural History, Complications and Prognosis

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.

Diagnosis

Symptoms

• Mental retardation usually severe;
• Hyperactive behavior, often with an outgoing personality;
• Severe constipation
• Seizures

Physical Examination

Appearance of the Patient

• Short stature

Head

• Macrocephaly
• Prominent forehead

Eyes

• Hypertelorism
• Down-slanting palpebral fissures

Throat

• Droopy, "open-mouthed" expression, a thin upper lip, a full or pouting lower lip due to hypotonia

Abdomen

• Inguinal hernia

Extremities

• Broad thumbs and great toes

Neurologic

• Severe hypotonia

Others

• Imperforate anus may be present
• Undescended testes (cryptorchidism)

Laboratory Findings

MRI

Partial or complete loss of corpus callosum

References

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