Spinal muscular atrophy (SMA) is an inherited neurological disease that affects the motor neurons in the body. The neurons turn dysfunctional and fail to aid muscle movement. This makes the muscles weak as they don’t receive signals for voluntary movement. Actions like swallowing and breathing become tough as the muscles involved in the process don’t receive the message to move. SMA can occur in different stages of life and shows symptoms accordingly. It is categorised as follows:

TYPE I

In the first type of SMA, infants experience hypotonia, a weakness in the muscles of their body, especially in their arms and legs. As a result they find it difficult to move, eat, swallow, and breathe. Parents might have to help infants to raise their body to make them sit. These symptoms can appear as early as within the first three months of being born. SMA, however, doesn’t affect cognition. So, infants in this early stage of SMA are usually alert, sharp and responsive.

TYPE II

SMA type II symptoms might become apparent between six to 12 months of age. Children might be able to sit or lie down and move their forearms. But, they will have trouble lifting their knees to their chest. In this stage, there’s a generalized muscle weakness. Walking without help becomes tough. Kids might experience difficulty in breathing and eating too. Other signs include tremor of the fingers and skeletal abnormalities like a hip dislocation.

Type III
In this type of SMA, patients have symptoms that appear gradually. For instance, they are able to walk initially, but may lose this ability over time. Breathing is normal in early stages too, but spine deformities that appear later might make it difficult to breathe. Children might also have slight tremors and poor balance which makes them feel clumsy. During SMA type III, symptoms begin to show from 18 months of age till adolescence.

Type IV
SMA type IV, also known as adult-onset SMA, affects people usually after they turn 35. Symptoms differ according to the extent to which adults are affected. Mostly, the ability to walk is retained, but in a few cases, people might need wheelchair assistance. Muscle weakness might progress from the legs to the hips, arms, and shoulders. Some people might show these symptoms as early as in their teen years.

Diagnosis
Based on the symptoms, the doctor will ask to conduct a blood test to diagnose SMA. Then, through genetic testing, the presence or absence of the SMN1 gene is noted. SMN1 and SMN2 genes form the survival motor neuron (SMN). This encoded neuron sends out proteins into the body that aids muscle function. According to Cleveland Clinic, 95 percent of those with SMN-related SMA, won’t have the SMN1 gene. And, in the remaining five percent, the gene might be mutated. Other than blood testing, doctors may also order an electromyography or a muscle biopsy to diagnose cases of SMA.