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Spinal muscular atrophy

Spinal Muscular Atrophy (SMA) is a term applied to a number of different disorders, all having in common a genetic cause and the manifestation of weakness due to loss of the motor neurons of the spinal cord and brainstem. more...

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Types

Caused by mutation of the SMN gene

The most common form of SMA is caused by mutation of the SMN gene, and manifests over a wide range of severity affecting infants through adults. This spectrum has been divided arbitrarily into three groups by the level of weakness.

  • Infantile SMA - Type 1 or Werdnig-Hoffmann disease (generally 0-6 months). SMA type 1, also known as severe infantile SMA or Werdnig Hoffmann disease, is the most severe, and manifests in the first year of life with the inability to ever maintain an independent sitting position.
  • Intermediate SMA - Type 2 (generally 7-18 months). Type 2 SMA, or intermediate SMA, describes those children who are never able to stand and walk, but who are able to maintain a sitting position at least some time in their life. The onset of weakness is usually recognized some time between 6 and 18 months.
  • Juvenile SMA - Type 3 Kugelberg-Welander disease (generally >18 months). SMA type 3 describes those who are able to walk at some time. It is also known as Kugelberg Welander disease.

Other forms of SMA

Other forms of spinal muscular atrophy are caused by mutation of other genes, some known and others not yet defined. All forms of SMA have in common weakness caused by denervation, i.e. the muscle atrophies because it has lost the signal to contract due to loss of the innervating nerve. Spinal muscular atrophy only affects motor nerves. Heritable disorders that cause both weakness due to motor denervation along with sensory impairment due to sensory denervation are known by the inclusive label Charcot-Marie-Tooth or Hereditary Motor Sensory Neuropathy. The term spinal muscular atrophy thus refers to atrophy of muscles due to loss of motor neurons within the spinal cord.

  • Hereditary Bulbo-Spinal SMA Kennedy's disease (X linked, Androgen receptor)
  • Spinal Muscular Atrophy with Respiratory Distress (SMARD 1) (chromsome 11, IGHMBP2 gene)
  • Distal SMA with upper limb predominance (chromosome 7, glycyl tRNA synthase)

Treatment

The course of SMA is directly related to the severity of weakness. Infants with the severe form of SMA frequently succumb to respiratory disease due to weakness of the muscles that support breathing. Children with milder forms of SMA naturally live much longer although they may need extensive medical support, especially those at the more severe end of the spectrum.

Although gene replacement strategies are being tested in animals, current treatment for SMA consists of prevention and management of the secondary effect of chronic motor unit loss. It is likely that gene replacement for SMA will require many more years of investigation before it can be applied to humans. Due to molecular biology, there is a better understanding of SMA. The disease is caused by deficiency of SMN (survival motor neuron) protein, and therefore approaches to developing treatment include searching for drugs that increase SMN levels, enhance residual SMN function, or compensate for its loss. The first effective specific treatment for SMA may be only a few years away, as of 2005.

Read more at Wikipedia.org


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There are other ways to manage spinal muscular atrophy type 1
To the Editor: The authors of a recent article in CHEST (September 2004) (1) described their management outcomes for patients with infantile spinal ...
Respiratory capacity course in patients with infantile spinal muscular atrophy
Study objectives: To describe the clinical and respiratory course in infantile spinal muscular atrophy (SMA) type I, type II, and type III, and to evaluate ...
Spinal Muscular Atrophy Type 1 - )
A Noninvasive Respiratory Management Approach Study objective: To determine whether spinal muscular atrophy (SMA) type 1 can be managed without tracheostomy ...
Severe obstructive sleep apnea in a patient with spinal muscle atrophy
Patients with spinal muscle atrophy (SMA) who survive to adulthood experience a slow, continuous loss of motor function but typically have a normal life expectancy. These patients, however, require
Age-dependent differences in androgen binding affinity in a family with spinal and bulbar muscular atrophy
Objectives: To investigate androgen receptor (AR) function in spinal and bulbar muscular atrophy (SBMA). Methods: A kindred was identified with five individuals ...
Indicators of need for mechanical ventilation in Duchenne muscular dystrophy and spinal muscular atrophy
Study objectives: The purpose was to investigate a possible relationship between different parameters of physical function, spirometric measurements, and the approaching need for mechanical ventilati
Use of power mobility for a young child with spinal muscular atrophy
Case Report Background and Purpose. Young children with severe motor impairments, such as spinal muscular atrophy, are often unable to move around their ...
Clinical & genetic analysis of four patients with distal upper limb spinal muscular atrophy
Background & objectives: Distal upper limb spinal muscular atrophy (SMA) is an uncommon segmental variant of SMA. The condition is usually sporadic, affects ...

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