Spinal Muscular Atrophy is a genetic, motor neuron disease that causes progressive degeneration of the anterior horn cells of the spinal cord which causes skeletal muscles to waste away.    Weakness is more severe in the legs than in the arms.  There are several different types of SMA.  The determination of which type is manifesting is dependant upon which physical milestones an affected child has met; it is important to note that the course of the disease is unique in each child.

SMA is an autosomal recessive disease, which means that both parents must be a carrier of the gene abnormality.  If both parents are carriers, there is a 1 in 4 chance that any of their children will have SMA.  1 in 6000 babies born are affected with SMA and 1 in 40 people are genetic carriers.  SMA is the number one genetic killer of infants and toddlers.  People with SMA are missing a gene called the SMN1 gene, which is responsible for the production of Survival Motor Neuron Protein.  Without this protein the nerve cells in the spine atrophy and eventually die.  When the nerve cells die, they are no longer able to send messages to make the muscles work.

-Type I  - Symptoms are floppiness of the limbs and trunk, decreased limb movements, swallowing and feeding difficulties and impaired breathing.   Also known as Werdnig-Hoffman disease, Type I is the most severe and usually diagnosed within the first few months of life.  Children affected with type I are never able to sit or stand.

-Type II - Symptoms usually appear between 3-15 months.  Symptoms usually include inability to stand or walk, respiratory problems, hypotonia, decreased or absent deep tendon reflexes and muscle fasciculations (tremor in limbs and/or tongue).  These children are usually able to sit unassisted and some are even able to stand at some point.   Scoliosis is often a complication with children that have type II.

-Type III - Symptoms may appear between ages 2-17 and include abnormal gait, trouble running, climbing stairs, rising from a chair, trouble getting up from the floor and fine tremors of the fingers.  Early motor milestones are often met on schedule.  Children with type III may at some point in later childhood or early adulthood lose the ability to walk due to growth spurts or illness.

-Type IV (adult onset) - Symptoms usually appear after the age of 35.  Type IV is defined of an onset of weakness after the age of 18.  It is usually slow progressing and swallowing and respiration is seldom affected.

 

Progress in the research towards a cure for SMA has made leaps and bounds in the last 10 years.  Here is a timeline of the recent discoveries

• 1995 the SMA gene was identified.
• 1996 Discovery of the SMN Protein.  SMA Carrier testing developed
• 1998 SMN Protein was discovered to be the biochemical defect in SMA.  The severity of the disease correlates to the amount of SMN Protein.
• 2000 SMA replicated in mouse model and shows that SMA could be corrected with large amounts of SMN Protein.
• 2002 Completion of largest SMA drug screening with over 1 million compounds tested, several showing promise for SMA.
• 2003 Project Cure announces two clinical trials, where the drug is shown to increase SMN Protein
• 2004 Project Cure nears end of Phase I clinical trials for Valproic Acid and Sodium Phenylbutyrate, both show promise in slowing progression of SMA.
• 2005 Motor neurons derived from embryonic stem cells can extend axons to innervate muscles.  Project Cure   announces Carni-Val clinical trial for type II and III children ages 2-17. 

 

Some of our favorite links for SMA info:

FSMA

Project Cure

SMA Support

AMSMART

SMA Foundation