FG syndrome

FG syndrome
Classification and external resources
OMIM	305450
DiseasesDB	32162
GeneReviews	MED12-related disorders

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]

Characteristics

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]

Genetics

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

History

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.

References

1 2 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.
1 2 Thompson E, Baraitser M (1987). "FG syndrome". J Med Genet 24 (3): 139–43. doi:10.1136/jmg.24.3.139. PMC 1049945. PMID 3572995.
1 2 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.

Cytoskeletal defects

Microfilaments

Myofilament

Actin	Hypertrophic cardiomyopathy 11 Dilated cardiomyopathy 1AA DFNA20 Nemaline myopathy 3

Myosin	Elejalde syndrome Hypertrophic cardiomyopathy 1, 8, 10 Usher syndrome 1B Freeman–Sheldon syndrome DFN A3, 4, 11, 17, 22; B2, 30, 37, 48 May-Hegglin anomaly

Troponin	Hypertrophic cardiomyopathy 7, 2 Nemaline myopathy 4, 5

Tropomyosin	Hypertrophic cardiomyopathy 3 Nemaline myopathy 1

Titin	Hypertrophic cardiomyopathy 9

Other

1/2	Keratinopathy (keratosis, keratoderma, hyperkeratosis): KRT1 Striate palmoplantar keratoderma 3 Epidermolytic hyperkeratosis IHCM KRT2E (Ichthyosis bullosa of Siemens) KRT3 (Meesmann juvenile epithelial corneal dystrophy) KRT4 (White sponge nevus) KRT5 (Epidermolysis bullosa simplex) KRT8 (Familial cirrhosis) KRT10 (Epidermolytic hyperkeratosis) KRT12 (Meesmann juvenile epithelial corneal dystrophy) KRT13 (White sponge nevus) KRT14 (Epidermolysis bullosa simplex) KRT17 (Steatocystoma multiplex) KRT18 (Familial cirrhosis) KRT81/KRT83/KRT86 (Monilethrix) Naegeli–Franceschetti–Jadassohn syndrome Reticular pigmented anomaly of the flexures

3	Desmin: Desmin-related myofibrillar myopathy Dilated cardiomyopathy 1I GFAP: Alexander disease Peripherin: Amyotrophic lateral sclerosis

4	Neurofilament: Parkinson's disease Charcot–Marie–Tooth disease 1F, 2E Amyotrophic lateral sclerosis

5	Laminopathy: LMNA Mandibuloacral dysplasia Dunnigan Familial partial lipodystrophy Emery-Dreifuss muscular dystrophy 2 Limb-girdle muscular dystrophy 1B Charcot–Marie–Tooth disease 2B1 LMNB Barraquer–Simons syndrome LEMD3 Buschke–Ollendorff syndrome Osteopoikilosis LBR Pelger-Huet anomaly Hydrops-ectopic calcification-moth-eaten skeletal dysplasia

Microtubules

Kinesin	Charcot–Marie–Tooth disease 2A Hereditary spastic paraplegia 10

Dynein	Primary ciliary dyskinesia Short rib-polydactyly syndrome 3 Asphyxiating thoracic dysplasia 3

Other	Tauopathy Cavernous venous malformation

Membrane

Ankyrin: Long QT syndrome 4

Hereditary spherocytosis 1

Catenin

APC
- Gardner's syndrome
- Familial adenomatous polyposis
plakoglobin (Naxos syndrome)
GAN (Giant axonal neuropathy)

Other

centrosome: PCNT (Microcephalic osteodysplastic primordial dwarfism type II)

See also: cytoskeletal proteins

Sex linkage: X-linked disorders

X-linked recessive

Immune	Chronic granulomatous disease (CYBB) Wiskott–Aldrich syndrome X-linked severe combined immunodeficiency X-linked agammaglobulinemia Hyper-IgM syndrome type 1 IPEX X-linked lymphoproliferative disease Properdin deficiency

Hematologic	Haemophilia A Haemophilia B X-linked sideroblastic anemia

Endocrine	Androgen insensitivity syndrome/Spinal and bulbar muscular atrophy KAL1 Kallmann syndrome X-linked adrenal hypoplasia congenita

Metabolic	Amino acid: Ornithine transcarbamylase deficiency Oculocerebrorenal syndrome Dyslipidemia: Adrenoleukodystrophy Carbohydrate metabolism: Glucose-6-phosphate dehydrogenase deficiency Pyruvate dehydrogenase deficiency Danon disease/glycogen storage disease Type IIb Lipid storage disorder: Fabry's disease Mucopolysaccharidosis: Hunter syndrome Purine-pyrimidine metabolism: Lesch–Nyhan syndrome Mineral: Menkes disease/Occipital horn syndrome

Nervous system	X-linked mental retardation: Coffin–Lowry syndrome MASA syndrome X-linked alpha thalassemia mental retardation syndrome Siderius X-linked mental retardation syndrome Eye disorders: Color blindness (red and green, but not blue) Ocular albinism (1) Norrie disease Choroideremia Other: Charcot–Marie–Tooth disease (CMTX2-3) Pelizaeus–Merzbacher disease SMAX2

Skin and related tissue	Dyskeratosis congenita Hypohidrotic ectodermal dysplasia (EDA) X-linked ichthyosis X-linked endothelial corneal dystrophy

Neuromuscular	Becker's muscular dystrophy/Duchenne Centronuclear myopathy (MTM1) Conradi–Hünermann syndrome Emery–Dreifuss muscular dystrophy 1

Urologic	Alport syndrome Dent's disease X-linked nephrogenic diabetes insipidus

Bone/tooth	AMELX Amelogenesis imperfecta

No primary system	Barth syndrome McLeod syndrome Smith–Fineman–Myers syndrome Simpson–Golabi–Behmel syndrome Mohr–Tranebjærg syndrome Nasodigitoacoustic syndrome

X-linked dominant

X-linked hypophosphatemia Focal dermal hypoplasia Fragile X syndrome Aicardi syndrome Incontinentia pigmenti Rett syndrome CHILD syndrome Lujan–Fryns syndrome Orofaciodigital syndrome 1 Craniofrontonasal dysplasia

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