WHAT IS SPINAL MUSCULAR ATROPHY?
SMA is in a class of degenerative motor neuron diseases, such as Muscular Dystrophy (MD), but is the most severe form of such diseases. It is suggested that SMA occurs one in 6000 to one in 20,000 births. SMA affects infants, children and adults worldwide. It is a complex disease affecting individuals across the lifespan for which to date, there is no known cure.
Spinal Muscular Atrophy (SMA) is a genetically transmitted condition whereby the nerves of the spinal cord (anterior horn cells) deteriorate, weaken and eventually die.
With SMA, the nerve cells of the spinal cord do not have the genetic programming that enables them to send messages effectively or efficiently to the muscles surrounding the spinal cord. Because the muscles are not stimulated, they become weak and the muscle cells “atrophy”, or die from lack of use. Muscle weakness becomes worse over time until the muscles no longer respond. Muscles closest to the trunk (shoulders, hips and back) are often the most severely affected, with leg weakness usually more pronounced than in the arms. Key life functions such as swallowing and feeding can be affected. Because of the involvement of respiratory muscles used for breathing and coughing, those with SMA are at significant risk of contracting pneumonia or experiencing other lung problems. Children with SMA who contract pneumonia face a great battle for life, a challenge from which many do not recover. Neck, head and facial muscles can be affected. With poor head control there is a risk that being unable to lift the head can result in cutting off the airway (airway occlusion).
Some children eventually lose the ability to suck, chew, drink, spit or smile.
Intelligence is unaffected and many health professionals are impressed that SMA children are very bright and alert, and are very interested in the people and activities going on around them. Children with SMA can experience normal feelings of touch, temperature, sensation and pain and otherwise appear normal in every way, except that they are extremely weak.
WHAT CAUSES SMA?
SMA is a recessive order caused by abnormalities by the SMNI gene (The Survival Motor Neuron 1 Gene). The SMN1 gene is located on chromosome 5. If the SMN1 gene has reduced or no function, then the motor neurons in the spinal cord and brainstem do not survive, and gradually die off.
Individuals with SMA have inherited two faulty copies of this gene, one from each parent. Parents of SMA children are usually unaware they carry the faulty genes and often have not heard of SMA until their child has been diagnosed. Two carriers will have a one in four chance of having an affected child in each pregnancy, a 50% chance of a child who is an unaffected carrier, and 25% chance of a child who does not have SMA and is not a carrier.
HOW MANY TYPES ARE THERE?
SMA is a very complex disease and each child and each set of parents face their own unique decisions. As SMA affects each child differently, it is important to care for the child in a way that best meets their specific needs and those of their family.
There are four clinical classifications of SMA Type 1 (Infantile SMA or Werdnig-Hoffman disease), Type 2 (Intermediate SMA or chronic childhood SMA), Type 3 (Juvenile SMA or Kugelberg-Welander disease) and type 4 (Adult onset Spinal Muscular Atrophy) although there are also rare variants.
HOW IS SMA DIAGNOSED?
Parents tend to raise concerns about noticeable weakness or reduced function in their Childs limbs. A physical examination reveals loss of, or reduced of tendon reflexes in the legs and weakness in both sides of the body (especially the legs). Other symptoms are fine twitches of the muscles in the limbs and tremor (fasciculation) of the tongue. Diagnosis is usually confirmed by blood test, which identifies the presence or absence of the SMNI1 gene. SMA type is then identified according to age and severity of symptoms, that is the younger the child the more severe the condition. Testing accurately diagnosis SMA in 95% of cases, though the rarer SMA variants that do not have deletion of SMN1 may not be diagnosed until further investigation occurs.
IS THERE A TREATMENT?
Unfortunately, there is no cure for SMA. Scientists have not yet been able to stop or reverse the nerve and muscle death or repair faulty genes.
To date there are no evidence based guidelines to inform the care of those affected by SMA, so the information and practise of health care professionals may vary. However experts around the world have produced a document termed “consensus statement for standard care in Spinal Muscular Atrophy. (Wang et al 2007) This document provides guidelines on how to best care for those affected with SMA, and is written by experts who have agreed, based on their experience and the available research evidence, on what is the most appropriate management of those living with SMA.
Importantly, the consensus statement suggests that rather than treat a person based on the type of SMA they have, it is more appropriate to provide care and treatment based on what they can do or their function. Function is described as:
- Non sitter – Cannot sit independently
- Sitter – Can sit but not walk independently
- Walker – Can walk independently
By managing the body’s systems (such as the respiratory or gastrointestinal system) according to the Childs level of function (as sitter, non sitter or walker) care and outcomes are better for the child.
The consensus statement recommends:
- Coordinated multidisciplinary care is offered by skilled professionals, such as neurologists or geneticists, occupational therapists, physiotherapists, nutritionist dieticians, speech pathologists, gastroenterology and pulmonary specialists for example as soon as such information is needed.
- Parents need information that will assist them to understand the disease process, the intervention and treatment options available to them, and the likely prognosis for their child.
- Care be coordinated with the family.
- Families have access to resources and information about SMA or access to support services or self help groups.
- At times, that choosing to intervene early (e.g. by inserting a nasogastric or feeding tube earlier than necessary) may be better handled by the child and prevent complications that may occur when the need for the intervention is greatest.
- (In the US) families have access to information about clinical trials,