What is Spinal Muscular Atrophy?

What is SMA?

Spinal Muscular Atrophy (SMA) is a genetic disorder that affects nerve cells so that muscles can't be used and become wasted, or atrophied.  

SMA is a genetic disease and types I, II and III are autosomal recessive conditions meaning that if both your parents are carriers, you have a 1 in 4 chance of having the condition, around one in 20,000 babies are affected with type one SMA.

SMA affects the nervous system in an area of the spinal cord called the anterior horn. The nerve cells become damaged, breaking the link between the brain and the muscles. As a result, the muscles do not receive messages from the brain telling them to move therefore can't be used and waste away (become atrophied). This can lead to problems with breathing as physical activities including crawling, walking, feeding and head control. There are 3 main types of spinal Muscular Atrophy, but there are also other variations below are the more known variations of the disease , and future Pregnancies present other options. Click below to find out more:

  • SMA Type I (Werdnig-Hoffman disease)

    Type 1 Is the most severe. It may present it' self before birth or shortly afterwards (mothers may notice decreased movement of the foetus late in pregnancy), and affected babies are rarely able to lift their head or develop normal movement. Swallowing, feeding and breathing may be difficult, and the child rarely survives to the age of two.


  • SMA Type II (moderate)

    Type 2 SMA usually appears in the first couple of years. The child can reach adulthood, but they may need help to sit or stand, and strain on the muscles can cause complications.   


  • SMA Type III (Kugelberg-Welander disease)

    Type 3 SMA is a milder form of SMA and may be diagnosed as late as adolescence. Those affected may have problems walking or getting up from sitting.

  • Adult Onset SMA

    Adult Onset SMA affects the lower motor neurones, in  most cases adult onset begins in 1 opart of the body eg, leg on onside of the body but may progress with time to both sides. Generally there is no pain, but symtoms that maybe experienced could include -  aching muscles, a feeling of heaviness, numbness, tingling and Fatigue.

  • SMARD - SMA with Respiratory Distress

    Spinal Muscular Atrophy with Respiratory Distress  (SMARD) is caused by mutations on the IGHMBP2 gene.  


    The predominating symptom is severe respiratory distress due to paralysis of the diaphragm.  Most sufferers of SMARD will experience respiratory failure within their first six months of life.  Many  die in their sleep and most do not live past their first birthday.  For those who survive, artificial ventilation is required, Progressive muscle weakness, follows the respiratory failure.  Cognitive function is unaffected.

  • Future Pregnancies

    When a family is considering further children there are various options available. Due to SMA being a genetic disorder, there is  25% chance of having an unaffected baby, a 50% chance of the child been a carrier of the condition and a 25% chance of  being affected. 


    The decision about which option to take is sensitive and personal to the family involved help  and support is available whatever path the family choose to take, the options available include:

       

    Taking a chance.Testing could be offered shortly after birth to confirm whether or not a baby is affected/unaffected or a carrier.

     

    Prenatal Diagnosis which involves testing at 12 weeks in to a  pregnancy by chorionic villus sampling (CVS) or amniocentesis at 16 weeks. thhese forms of diagnosis can determine whether or not the child is affected.  If the child is affected the family can decide to not continue with the pregnancy. 


    Preimplantation Genetic Diagnosis (PGD) is basically a form of IVF,  after the fertilisation of the eggs by the sperm a sample of the embryos cells are extracted, The cells are then tested to see if they are affected or unaffected. 


    unaffected embryos are transferred to the womb and after 12 weeks a pregnancy test is carried 12 days later to determine wether there is a pregnancy . This is a lengthy process but avoids termination of an affected pregnancy, unfortunately PGD can also be expensive and has limited success.