Spinal Muscular Atrophy

Spinal muscular atrophy is a very serious condition that leads to a gradual loss of mobility. SMA is a genetic condition that affects around 1 in every 6,000 births. SMA affects the motor neurons in the spinal cord; over time the conditions causes the motor neurons in the anterior horn part of the spine to deteriorate; this causes muscle degeneration, a lack of mobility and a gradual loss of motor function (this means a patient gradually loses the ability to move parts of their body).

There are many different types of SMA; these include

  • Type 0: this is the most serious form of SMA; it can usually be detected during weeks 30 to 36 of pregnancy as the movement of the foetus is restricted.
  • Type l: this is serious condition which affects the baby’s proximal muscles (the muscles in the centre of the body including the chest, back, shoulders and hip muscles). This form of SMA is usually identified at birth.
  • Type ll (also known as Dubowitz disease): this form of SMA usually develops in children aged between 6 and 12 months. It is milder than types 0 and l.
  • Type lll: also known as Kugelberg-Welander disease, this condition is the mildest type of childhood SMA. It is usually found in children over the age of 2.
  • Type lV: this develops in adulthood, usually after the age of 35; in comparison with other types of SMA the symptoms are mild.

What causes SMA?

SMA is caused by a defective gene known as the SMN1 gene (spinal motor neuron 1). The condition is an autosomal recessive condition which means that it can be passed on to children only when both parents carry the defective gene and it is not inherited via the sex chromosomes. Many people are carriers of the gene that causes SMA (approximately 1 in 40 people); this means they have only one SMN1 gene instead of two. If both parents have the defective gene there is 50 percent chance their baby will carry the defective gene and a 25 percent chance their baby will develop or be born with SMA. Adult SMA can be caused by genetic mutation of the SMN1 gene or as a result og carrying the gene from either one or both parents.

Symptoms of SMA

SMA is a condition that has no effect on a person’s mental health; symptoms are entirely physical. The severity and nature of the symptoms vary according to the type of condition the person has:

  • Type 0: babies with type 0 SMA usually have difficulties with breathing and swallowing and have a very limited range of movement.
  • Type l: babies with type l SMA have very weak muscles, which means they have problems with moving, breathing and swallowing. The life expectancy for babies born with type l SMA is very short, with most passing away before their second birthday.
  • Type ll: children with type ll SMA will experience difficulties with breathing and moving because their proximal muscles are often very weak. They may deteriorate as they get older and they may develop conditions relating to the shape and strength of their bones; this often causes their range of movement to become severely restricted.
  • Type lll: children with type lll SMA may have problems with movement and balance and many may find it difficult to stand for long periods of time without support. Symptoms usually develop after 12 months of age.
  • Type IV: symptoms usually appear gradually after the age of 35; they are generally much less severe in adults than in children. Common symptoms include muscle cramps and spasms, weakness in the muscles and speech problems.
  • Kennedy’s syndrome (a form of adult SMA): symptoms may include shaky hands, muscle spasms and cramps, facial muscle spasms, speech problems and difficulty swallowing.

Treatment for SMA

There is currently no cure for SMA but research in this area is ongoing. Treatments can be offered to help with some of the symptoms of SMA; often physiotherapy is used to help with breathing, improve muscle tone and gradually increase the range of movement around the joints. Babies that have difficulty feeding because they find it hard to swallow are usually fed through a tube. Patients with SMA are encouraged to exercise regularly; exercise is often gentle and patients are supported by other people but it is important to keep muscles working and the circulatory system in good shape. Some patients may wear a back brace to support the muscles and bones in their chest and back and reduce the likelihood of suffering from scoliosis (curvature of the spine).

Guide to Bone and Muscle Disorders

Bone and Muscle



Muscular dystrophy



Pagets disease

Spina bifida

Spinal muscular atrophy

Living with a disability