SMA is a genetic condition, caused by a change to a gene called SMN1. This change leads to a damage of nerves that control your muscles. These nerves are called motor neurons. When motor neurons break down, they cannot send signals to your muscles to make muscles move. Without these signals, muscles become weak and get smaller.
Symptoms of SMA
SMA is something you are born with, but symptoms might not develop right away. People can start becoming weak from SMA in infancy, childhood or even during adult years. The most common presentation can occur in young infants and is the most severe form. Children with this presentation would be described as “floppy” and may miss important developmental milestones such as rolling, sitting or walking when expected. Older infants might be able to roll and sit, but develop weakness that prevents them from standing or walking. Toddlers and young children could start falling more and being unable to walk or run as fast as other children their age.
Because of this range of weakness and symptoms, we used to divide SMA into “types,” with the type 1 SMA being the most severe presentation (an infant who never was able to roll), type 2 SMA describing an infant who could sit at some point but never stand and type 3 SMA patients presenting in early childhood, after being able to stand. We are using this classification less and less, because it does not take into account the effects of early diagnosis and treatment of SMA.
Diagnosis of SMA is typically made by genetic testing.
If you or a member of your family has a known history of a carrier status or other family member diagnosed with SMA, there are testing options that can be discussed before or during pregnancy with a genetic counselor.
Parents can be tested for carrier status. This will determine the need to test children.
Children can be tested during pregnancy if deemed necessary and safe. This typically includes chorionic villus sampling or amniocentesis. As SMA is a treatable condition, determining the status of your child allows for planning and prompt treatment following birth.
Luckily for us, Wisconsin, is one of 32 states that has added SMA testing to be included as part of the newborn screening panel. This means that 24 hours after birth, whether in a medical institution or other arrangement, a heel prick is completed and tested for this condition through our state testing lab.
Genetic testing also can be arranged for any person if SMA is suspected.