A group of genetic disorders characterized by degeneration of nerve cells in the spinal cord that results in muscle weakness and atrophy is known as the spinal muscular atrophy. Spinal muscular atrophy has four different types, namely, type I, II, III, and IV. Each type of spinal muscular atrophy displays a different set of symptoms. Doctors often diagnose the type of spinal muscular atrophy a person is suffering from by studying the symptoms.

Type I
Type I spinal muscular atrophy is one of the most severe forms that is often diagnosed at a very early stage, i.e., in the first few months after birth. This condition delays the physical development in most infants and refrains them from having the ability to support their head or sit unassisted. The common symptoms that children show when they suffer from this health condition include problems in breathing; swallowing, which may cause choking; tremors; lack of tendon reflexes; fasciculations; and hypotonia, which is the condition of severely reduced muscle tone.

The type I of spinal muscular atrophy is a life-limiting condition that results in the life expectancy of fewer than 18 months.

Type II
Type II of spinal muscular atrophy begins between the age of 6 to 18 months. Children who suffer from type II spinal muscular atrophy are able to sit without assistance, but often need help in getting into the seated position. These children are also unable to stand or walk without an aid.

The lifespan of spinal muscular type II disorder is not known with certainty; however, most kids who suffer from this health condition often live into their early adulthood, and with proper care, they also live well into adulthood.

Type III
The symptoms of type III spinal muscular atrophy often appears after the first 18 months of a child’s life. However, in some cases, it also appears in their late childhood or early adulthood. As compared to children with type I and type II spinal muscular atrophy, individuals with type III condition have more strength in their hands and legs. However, they do face difficulty in climbing stairs.

The life expectancy of people with type III spinal muscular atrophy is the same as normal people; however, they do suffer from problems in swallowing and breathing throughout their lives.

Type IV
The type IV spinal muscular atrophy affects adults, especially, in their second or third decade of life. The symptoms are often progressive muscle weakness, tremors, and twitching. These symptoms progress throughout their lives and are between mild and moderate.

This type of spinal muscular atrophy does not affect the life expectancy of an individual and those with this type are also able to walk until they are 60 years or above of age.