In order for a child to be affected by SMA, both parents must be carriers of the abnormal gene and both must pass this gene on to their child. When both parents are carriers, there is a 25% chance of the child inheriting the disorder.
As a child with SMA develops, their body is under great stress due to the decrease in motor neurons. This results in muscle atrophy, which causes weakness, difficulty breathing and bone and spinal deformities.
The disease is diagnosed as Types I, II, and III. Type I (which was what Andrew had) is evident at birth or within the first few months of life. Symptoms include floppy limbs and trunk, feeble movements of the arms and legs, swallowing and feeding difficulties and impaired breathing. Children with this type usually have the shortest lifespan, as it is the most serious.
Type II typically begins between 6 and 18 months of age. Legs tend to be more impaired than arms. Children with Type II may able to sit and some may be able to stand or walk with help.
Symptoms of Type III appear between 2 and 17 years of age and include difficulty running, climbing steps, or rising from a chair. The lower extremities are most often affected. Complications include scoliosis and chronic shortening of muscles or tendons around joints.
Sadly, the majority of children born with Type I die before the age of two. Those with Types II and III can live considerably longer, sometimes into adulthood.
For more information, log on to Families of SMA at: www.fsma.org