What is Spinal Muscular Atrophy (SMA)?

Spinal muscular atrophy (SMA) is a group of genetic diseases that cause weakness and wasting in the voluntary muscles of infants and children. With SMA, as the spinal cord motor neurons begin to shrink and die, the child’s brain is no longer able to control the body’s voluntary muscles, especially those in the arms and legs and in the head and neck. The muscles begin to weaken and waste away. This weakening and wasting away of muscles affects movements such as walking, crawling, head and neck control, swallowing, and breathing. It is a one of the most common genetic conditions affecting children. It is estimated that one in every 6,000 to 10,000 babies worldwide is born with SMA.

There are 4 types of SMA: Type 1 (severe), Type 2 (intermediate), Type 3 (mild), and Type 4 (adult). The classification is determined by the developmental milestones the child has hit by the time of the disease onset. Types 1 and 2 are the most common. Type 1 (severe) SMA is also called Werdnig-Hoffmann Disease. It is the most severe and the most common type of SMA. It is usually evident at birth, or in the first few months after birth (0-6 months). Symptoms include floppy limbs and weak trunk movement. Children with this type usually have very limited ability to move. They will also have a hard time feeding and swallowing, holding their head up, and breathing, as well as never being able to sit. Type 1 SMA progresses very rapidly.

Type 2 (intermediate) SMA usually appears between the ages of 7 to 18 months. SMA Type 2 affects the child's legs more than his or her arms. Children with SMA Type 2 can never stand without external support. Respiratory infections are also common with this type of SMA. Type 3 (mild) SMA is also called Kugelberg-Welander or Juvenile Spinal Muscular Atrophy. Symptoms can first appear anywhere from 18 months to early adulthood. Patients with Type 3 SMA can stand and walk, but may have trouble getting up from sitting position. They may also experience mild muscle weakness and are at greater risk for respiratory infections. Type 4 (adult) SMA is rare and doesn’t usually emerge until the second or third decade of life. Patients with Type 4 SMA can walk during adulthood but will usually experience slowly progressive muscle weakness and other typical SMA symptoms.

 

 

How is SMA treated in a child?

Unfortunately, there is currently not a cure for SMA. However, there is a potential cure in the works in the form of genetic resequencing, and is now FDA approved for children under 2 years old. There is also a medicine called Spinraza that is currently helping children with SMA progress instead of regress.

Physical Therapy for children affected with SMA is focused on treating their symptoms, preventing complications, and improving their quality of life. Your Physical Therapist will be able to determine the best treatment for your child based on the type of SMA, the severity of the condition, and his or her age.