Clinical Blog: Spinal Muscular Atrophy

Spinal Muscular Atrophy is an autosomal recessive disease caused by a defect in the SMN1 gene.  This gene codes the SMN protein which is essential for motor neuron survival.  The lack of the SMN protein results in functional loss of motor neurons in the anterior horn of the spinal cord.  Located on human chromosome 5 at location 5q13 are two quite similar genes, SMN1 and SMN2.  SMN2 can only code approximately 10-20% of functional SMN protein (SMN-fl).  All SMA patients retain at least 1-4 copies of the SMN2 gene which allows some level of normal SMN protein production and some survival of motor neurons.  The severity of SMA is related to the number of copies of SMN2 and their ability to produce SMN-fl.

The clinical manifestations include progressive muscle wasting/weakness as a result of the lack of motor neuron function, poor muscle tone, delays in motor development, respiratory compromise with ventilator dependency a possibility, areflexia in extremities, fisted hands, fasciculations of the tongue, oral motor difficulties, and weight loss.  Muscle weakness can lead to orthopedic issues such as spinal kyphosis or scoliosis and equinus deformity of the foot. TLSO (thoracic/lumbar/sacral orthosis) and ankle orthotics may be used to prevent or reduce progression of skeletal  issues.  Oral motor limitations in (SMA I, II) can lead to gastrostomy tube placement to provide necessary nutrition.  Their cognitive development is usually normal to slightly advanced.

sma kiddoThere are several types of SMA classified by the age of onset of the symptoms which include:

  • Werdnig-Hoffmann (Type I)
    • Werdnig-Hoffmann or infantile SMA is evident at birth or shortly thereafter with rapid death of dysfunctional neurons producing a “floppy baby syndrome” as well as respiratory compromise usually requiring tracheostomy with ventilation.
    • They are completely dependent in all functional tasks. Life expectance is often very limited from a few weeks to 2 years.
    • However, 10% of SMA 1 with milder phenotypes and with effective respiratory support can live into adolescence or adulthood.
  • Dubowitz (Type II)
    • Manifests between 6- 18 months of age with the child able to sit with or without assistance, but unable to advance much past this, with standing and walking usually unattainable.
    • The progression can vary. Respiratory limitations are a concern and carefully managed per individual.
    • Longevity is often into adulthood.
  • Kugelberg-Welander (Type III)
    • Kugelberg-Welander usually presents about 18 months of age.
    • These clients are often independent in standing and walk without support to a degree. Ambulation may deteriorate with time with client requiring wheeled mobility at some point.
    • Respiratory involvement is much less and life expectancy is fairly normal.
  • Adulthood Onset (Type IV)
    • Develops in adulthood near third decade of life with muscle weakness in proximal muscles of the extremities noted and possible need for wheeled mobility with progression.
    • Respiratory complications are rare and life expectancy is normal.

SMA I and severe cases of SMA II are much more compromised usually requiring ventilation and support for upright sitting secondary to their poor head, trunk and extremity control against gravity.  They also require tilt in space to reduce gravity’s negative impact on their weak torso, to position effectively for g-tube feedings (to prevent GERD), provide pressure relief, aid in head control and visual regard, as well as aid positioning for tracheostomy /respiratory care.  Recline can allow diaper changes without the need to transfer client with all the ventilation tubing to another surface, allow age appropriate full rest when out in the community, and aid caregiver with ventilator needs (tracheostomy changes, suctioning).

The Trekker, by Convaid, is ideal for this population.  The Trekker provides all the positional changes – tilt & recline-, seating options, and accommodates ventilator and G-tube needs, while still remaining extremely lightweight.

For more information on the Trekker go to

For Trekker product specifics, feel free to visit the following videos:

Article was written by Karen Missy Ball, MT, PT, ATP heads up Convaid’s CEU courses for physical therapists and other prescribers. She is the former Acting director and Assistant Director of the Physical Therapy Department at Children’s Hospital in New Orleans and was co-director of the seating program at Children’s for a decade while she also acted as a consultant to United Cerebral Palsy Center’s seating clinic. Missy was the educational specialist for Freedom Designs for 16 years. Presently, she has a private practice specializing in pediatric neurology clientele for treatment and equipment needs and continues to lecture globally on the topic of seating and mobility. Missy is an ATP and certified in pediatric NDT with a solid focus on improving function through treatment and equipment. Prior to her PT career, she practiced as a laboratory scientist specializing in Hematology. She attended Louisiana State University Medical Center for both Medical Technology (1977) and Physical Therapy (1984). She has been working as a health care professional for over 34 years.


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