Spinal muscle atrophy (SMA) is a disease imbibed in the genes and is recognized by limited or complete loss of nerve cells and motor neurons that help muscles move. These cells situated in the spinal cord cause difficulty in movement and weakness. There are various types of SMA but broadly classified as type 1, 2, 3, and 4, depending on age and symptoms. Read on to know more about the different types of spinal muscle atrophy.

• SMA Type 1

This is the most common type and also referred to as infantile-onset SMA or Werdnig-Hoffmann disease. Its symptoms can be seen when a child is born or it may occur within the first six months. Infants with this condition have weak limbs and have trouble raising their head. The typical lifespan of babies with this condition is 12 to 18 months.

• SMA Type 2

Also called intermediate SMA, this occurs in babies or toddlers who are about six to eighteen months old. They are able to sit without assistance but cannot stand up or walk. They also experience tremors and sometimes develop joint problems such as a curved spine. Babies with this condition suffer from acute respiratory challenges that can become worse as the condition grows.

• SMA Type 3

This type is also called juvenile SMA or Kugelberg-Welander syndrome. Symptoms develop after three years of age, but signs can remain hidden until a patient becomes a teenager. Individuals suffering from SMA Type 3 may be able to walk and stand without assistance, but may lose the ability to do this as they age. This type does not affect the patient’s lifespan.

• SMA Type 4

Adult-onset SMA or SMA Type 4 sometimes occurs in early adulthood or after 30 to 35 years of age. This type is rare and causes mild to moderate weakness in limbs, difficulty in walking, and other movement impairments. This condition may only get worse with time but does not cause any respiratory or breathing issues. Type 4 is usually not a life-threatening condition.

• Rarer types of SMA

Distal Spinal Muscular Atrophy type V (DSMA-V) is a progressive condition with symptoms that begin anytime during adolescence to mid-thirties. Spinal and Bulbar Muscular Atrophy (SBMA) or Kennedy’s disease is an inherited condition that happens in men. This condition has an X-linked recessive inheritance pattern and affects the androgen receptor (AR) gene. X-linked Spinal Muscular Atrophy affects the UBA1 gene and occurs in infants. Information on this type is limited since it is rare.

• Uncommon types of SMA

SMA with Lower Extremity Predominance (SMA-LED) is an autosomal dominant inheritance pattern that affects the DYNC1H1 gene. SMA with Progressive Myoclonic Epilepsy (SMA-PME) is a neurological disorder that affects the ASAH1 genes and has an autosomal recessive inheritance pattern. Spinal Muscular Atrophy with Respiratory Distress 1 (SMARD1) is an uncommon inherited disease caused by the IGHMBP2 gene.