A brief overview of the 4 types of SMA
A rare genetic condition, spinal muscular atrophy (SMA), affects one in six to ten thousand people. This condition causes an impairment in the individual’s ability to control their muscle movement. The main cause of the condition is a gene mutation; however, the symptoms, onset, and progress of the condition can be significantly different in every case. This is why SMA is broadly divided into four different types to provide information for physicians. Following is information about the four types of SMA for physicians:
Type 1 SMA– Type 1 SMA is also referred to as infantile-onset SMA or Werdnig-Hoffmann disease. The main cause of this condition is possession of only two copies of the SMN2 gene. This is the most common type of SMA and more than half the patients are diagnosed with the type 1 SMA. The symptoms for this type start within the first six months of birth. They include weak cries; difficulty in moving, swallowing, or breathing; hypotonia (weak or floppy arms and legs); and inability to sit without support. Babies usually did not survive type 1 SMA, but with more information on SMA for physicians with new research and technology, a drastic change in the survival rate has been noted.
Type 2 SMA– This type of SMA is also known as the intermediate SMA and, in most cases, individuals with type 2 SMA have a minimum of SMN2 genes. The symptoms start a little later when the baby is 7 to 18 months old. They can be less severe than type 1 in some cases. Symptoms include difficulty in standing, weak arms and legs, scoliosis (curved spine), coughing, and tremors in the fingers and hands. This type of the condition can reduce the life expectancy, but a large number of people with type 2 SMA survive into adulthood.
Type 3 SMA– It is also known as the late-onset SMA or mild SMA. The symptoms for this condition are specific. Individuals with this condition have four to eight SMN2 genes. The symptoms begin after 18 months of age and are usually diagnosed at the age of 3. In some cases, the symptoms can be delayed and can only be encountered in the early parts of adulthood. They include difficulty in getting up from seated positions, balance issues, scoliosis, and a difficulty in climbing steps or running. This type does not alter the life expectancy, but it comes with the risk of obesity.
Type 4 SMA– Also referred to as the adult-onset SMA, individuals with this condition have four to eight SMN2 genes. This is the least common type of all four types. Symptoms for this type usually occur post 35 years of age. They include weakness in the hands and feet, difficulty in walking, and shaking or twitching of muscles.