X-linked spinal muscular atrophy type 2

This article is about a neuromuscular disorder of boys caused by a genetic defect in the UBA1 gene. For other conditions with similar name, see Spinal muscular atrophies.

X-linked spinal muscular atrophy type 2
Classification and external resources
OMIM	301830

X-linked spinal muscular atrophy type 2 (SMAX2, XLSMA), also known as arthrogryposis multiplex congenita X-linked type 1 (AMCX1), is a rare neurological disorder involving death of motor neurons in the anterior horn of spinal cord resulting in generalised muscle wasting (atrophy). The disease is caused by a mutation in UBA1 gene and is passed in a X-linked recessive manner by carrier mothers to affected sons.^[1]^[2]

Affected babies have general muscle weakness, weak cry and floppy limbs; consequently, the condition is usually apparent at or even before birth. Symptoms resemble the more severe forms of the more common spinal muscular atrophy (SMA); however, SMAX2 is caused by a different genetic defect and only genetic testing can correctly identify the disease.

The disorder is usually fatal in infancy or early childhood due to progressive respiratory failure, although survival into teenage years have been reported.^[3] As with many genetic disorders, there is no known cure to SMAX2. Appropriate palliative care may be able to increase quality of life and extend lifespan.

References

↑ Ramser, J.; Ahearn, M. E.; Lenski, C.; Yariz, K. O.; Hellebrand, H.; Von Rhein, M.; Clark, R. D.; Schmutzler, R. K.; Lichtner, P.; Hoffman, E. P.; Meindl, A.; Baumbach-Reardon, L. (2008). "Rare Missense and Synonymous Variants in UBE1 Are Associated with X-Linked Infantile Spinal Muscular Atrophy". The American Journal of Human Genetics. 82 (1): 188–193. doi:10.1016/j.ajhg.2007.09.009. PMC 2253959. PMID 18179898.
↑ Dressman, D.; Ahearn, M. E.; Yariz, K. O.; Basterrecha, H.; Martínez, F.; Palau, F.; Barmada, M. M.; Clark, R. D.; Meindl, A.; Wirth, B.; Hoffman, E. P.; Baumbach-Reardon, L. (2007). "X-linked infantile spinal muscular atrophy: Clinical definition and molecular mapping". Genetics in Medicine. 9 (1): 52–60. doi:10.1097/GIM.0b013e31802d8353. PMID 17224690.
↑ Kobayashi, H.; Baumbach, L.; Matise, T. C.; Schiavi, A.; Greenberg, F.; Hoffman, E. (1995). "A gene for a severe lethal form of X-linked arthrogryposis (X-linked infantile spinal muscular atrophy) maps to human chromosome Xp11.3–q11.2". Human Molecular Genetics. 4 (7): 1213–1216. doi:10.1093/hmg/4.7.1213. PMID 8528211.

Dlamini, N.; Josifova, D. J.; Paine, S. M. L.; Wraige, E.; Pitt, M.; Murphy, A. J.; King, A.; Buk, S.; Smith, F.; Abbs, S.; Sewry, C.; Jacques, T. S.; Jungbluth, H. (2013). "Clinical and neuropathological features of X-linked spinal muscular atrophy (SMAX2) associated with a novel mutation in the UBA1 gene". Neuromuscular Disorders. 23 (5): 391–398. doi:10.1016/j.nmd.2013.02.001. PMID 23518311.
Baumbach-Reardon L.; Sacharow S.; Ahearn M. E. "Spinal Muscular Atrophy, X-Linked Infantile." 30 Oct 2008 [Updated 13 Sep 2012]. In: Pagon R. A.; Adam M. P.; Ardinger H. H.; et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2014. Available from: www.ncbi.nlm.nih.gov/books/NBK2594.

Pathology of the nervous system, primarily CNS (G04–G47, 323–349)

Inflammation

Brain	Encephalitis Viral encephalitis Herpesviral encephalitis Limbic encephalitis Encephalitis lethargica Cavernous sinus thrombosis Brain abscess Amoebic

Spinal cord	Myelitis: Poliomyelitis Demyelinating disease Transverse myelitis Tropical spastic paraparesis Epidural abscess

Both/either	Encephalomyelitis Acute disseminated Myalgic Meningoencephalitis

Brain/
encephalopathy

Degenerative

Extrapyramidal and movement disorders	Basal ganglia disease Parkinsonism PD Postencephalitic NMS PKAN Tauopathy PSP Striatonigral degeneration Hemiballismus HD OA Dyskinesia Dystonia Status dystonicus Spasmodic torticollis Meige's Blepharospasm Athetosis Chorea Choreoathetosis Myoclonus Myoclonic epilepsy Akathisia Tremor Essential tremor Intention tremor Restless legs Stiff person

Dementia	Tauopathy Alzheimer's Early-onset Primary progressive aphasia Frontotemporal dementia/Frontotemporal lobar degeneration Pick's Dementia with Lewy bodies Posterior cortical atrophy Vascular dementia

Mitochondrial disease	Leigh disease

Demyelinating

Episodic/
paroxysmal

Seizure/epilepsy	Focal Generalised Status epilepticus Myoclonic epilepsy

Headache	Migraine Familial hemiplegic Cluster Tension

Cerebrovascular	TIA Amaurosis fugax Transient global amnesia Acute aphasia Stroke MCA ACA PCA Foville's Millard–Gubler Lateral medullary Weber's Lacunar stroke

Sleep disorders	Insomnia Hypersomnia Sleep apnea Obstructive Congenital central hypoventilation syndrome Narcolepsy Cataplexy Kleine–Levin Circadian rhythm sleep disorder Advanced sleep phase disorder Delayed sleep phase disorder Non-24-hour sleep–wake disorder Jet lag

CSF

Other

Spinal cord/
myelopathy

Both/either

Degenerative

SA	Friedreich's ataxia Ataxia telangiectasia

MND	UMN only: Primary lateral sclerosis Pseudobulbar palsy Hereditary spastic paraplegia LMN only: Distal hereditary motor neuronopathies Spinal muscular atrophies SMA SMAX1 SMAX2 DSMA1 Congenital DSMA SMA-PCH SMA-LED SMA-PME Progressive muscular atrophy Progressive bulbar palsy Fazio–Londe Infantile progressive bulbar palsy both: Amyotrophic lateral sclerosis

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 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

Disorders of translation and posttranslational modification

Translation

Initiation factor: Leukoencephalopathy with vanishing white matter

snRNP: Retinitis pigmentosa 33

Posttranslational modification

Protein folding	Alzheimer's disease Huntington's disease Creutzfeldt–Jakob disease chaperonins: 3-Methylglutaconic aciduria 5

Protein targeting	I-cell disease

Ubiquitin	E1: X-linked spinal muscular atrophy 2 E3: Johanson–Blizzard syndrome Von Hippel–Lindau disease 3-M syndrome Angelman syndrome Deubiquitinating enzyme: Machado–Joseph disease Aneurysmal bone cyst Multiple familial trichoepithelioma 1

SUMO	OFC10

Other	Multiple sulfatase deficiency Hyperproinsulinemia Ehlers–Danlos syndrome 6

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X-linked spinal muscular atrophy type 2

See also

References

Further reading