Spinal muscular atrophy is a genetic illness characterized by muscle wasting and weakness. This happens due to the loss of motor neurons or anterior horn cells in the spinal cord. These are the cells responsible for transmitting impulses from the brain to the muscles and back for movements. These are the different types of spinal muscular atrophy divisions:

Type 0 Spinal Muscular Atrophy
This type affects children in the womb. Also known as the prenatal onset of SMA, it is characterized by limited fetal movements, difficulty in breathing, and difficulty in swallowing.

Type 1 Spinal Muscular Atrophy
Also known as Werdnig-Hoffmann Disease, this type is very common. It is also a severe type of spinal muscular atrophy. The signs of it are obvious at the birth of the patient or are indicated quite significantly in the first six months after birth. Kids affected by Type 1 Spinal Muscular Atrophy mostly have very limited ability to move with symptoms like floppy limbs and a weak movement. 

Type 2 Spinal Muscular Atrophy
This type of disorder starts showing its symptoms in children between the ages group of 7 to 18 months. It shows a significant effect on the legs as compared to the arms. This is why children affected by this type of spinal muscular atrophy cannot stand. Some of the patients may also find difficulty in sitting, if not treated. The life expectancy of patients with Type 2 is mostly till young adulthood and depends on how fast the illness progresses. Breathing problems are also common in patients of Type 2 spinal muscular atrophy.

Type 3 Spinal Muscular Atrophy
The different types of spinal muscular atrophy are also categorized based on the age of the patients. Type 3 shows symptoms in children over 18 months of age. This is the milder type among Type 1, 2, and 3 of muscular atrophy. The range of age in which the symptoms can appear for this type is also quite broad. Children affected by Type 3 of spinal muscular atrophy can stand and sit but may find it difficult to get up after sitting. Some patients may also have scoliosis which is characterized by shortening of muscles and tendons, restricting the free movement of the joints. Some of the patients may also be able to walk with a different gait. They may also have trouble climbing steps or running. A bit of a tremor in the fingers and respiratory issues can also be experienced in some. Getting the right treatment at the proper time can also help in getting a normal life expectancy.

Type 4 Spinal Muscular Atrophy
This is the rarest form among all the different types of spinal muscular atrophy. The symptoms for this type are seen only after a person completes 21 years of age. This type is characterized by muscle weakness which may progress slowly. Most patients don’t have any trouble walking. The Type 4 or adult muscular atrophy has no effect on the life expectancy.