Spinal muscular atrophy

Spinal muscular atrophy
Location of neurons affected by spinal muscular atrophy in the spinal cord
Classification and external resources
Specialty	Medical genetics
ICD-10	G12.0-G12.1
ICD-9-CM	335.0-335.1
OMIM	253300 253550 253400 271150
DiseasesDB	14093 32911
MedlinePlus	000996
eMedicine	Spinal Muscular Atrophy Spinal Muscle Atrophy Kugelberg–Welander SMA
Patient UK	Spinal muscular atrophy
MeSH	D014897
GeneReviews	Spinal Muscular Atrophy
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Spinal muscular atrophy (SMA), also called autosomal recessive proximal spinal muscular atrophy in order to distinguish it from other conditions with similar name, is a rare neuromuscular disorder characterised by loss of motor neurons and progressive muscle wasting, often leading to early death.

The disorder is caused by a genetic defect in the SMN1 gene, which encodes SMN, a protein widely expressed in all eukaryotic cells and necessary for survival of motor neurons. Lower levels of the protein results in loss of function of neuronal cells in the anterior horn of the spinal cord and subsequent system-wide muscle wasting (atrophy).

Spinal muscular atrophy manifests in various degrees of severity, which all have in common progressive muscle wasting and mobility impairment. Proximal muscles and lung muscles are affected first. Other body systems may be affected as well, particularly in early-onset forms of the disorder. SMA is the most common genetic cause of infant death.

Spinal muscular atrophy is an inherited disorder and is passed on in an autosomal recessive manner.

In December 2016, nusinersen became the first approved drug to treat SMA while several other compounds remain in clinical trials.

SMA manifests over a wide range of severity, affecting infants through adults. The disease spectrum is variously divided into 3–5 types, in accordance either with the age of onset of symptoms or with the highest attained milestone of motor development.

The most commonly used classification is as follows:

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Wikipedia