SMA is divided into subtypes based on age of onset and maximum function achieved. SMA types 0, 1, 2, 3 and 4 are inherited as autosomal recessive genetic disorders and are associated with mutations in the SMN1 gene, which is located on chromosome 5.1

Spinal Muscular Atrophy Type 4

SMA type 4, also called adult-onset SMA, is usually diagnosed in the second or third decade of life, usually after 35 years old, although some people may have symptoms as early as their later teenage years.2 These patients usually are ambulatory until around age 60.1

Symptoms of SMA type 4 include mild muscle weakness, scoliosis (curvature of the spine), tremor, and twitching.2 Complications include joint contractures, pneumonia, and metabolic abnormalities such as severe metabolic acidosis and dicarboxylic aciduria.

Weakness progresses very gradually, first affecting the thighs and hips, and then upper arms and shoulders. Life expectancy is normal, and swallowing and breathing functions are rarely affected.

People with spinal muscular atrophy type 4 may walk, and only a small number of them will require wheelchair assistance. Despite a set pattern of weakness, patients differ in the extent to which they are affected. Intelligence is not affected.

Physiotherapy and occupational therapy can be useful to determine appropriate aids, adaptive equipment, and home/school/work modifications that help people to maintain independence, mobility and energy. It is also important to prevent extra weight gain for better ease of movements. Hydrotherapy may also be beneficial.2

For some people with SMA type 4, no SMN1 gene mutations are found and often, in these cases, the genetic cause can’t be found. The diagnosis is based on clinical history and examination.

Read the latest news about SMA type 4 at SMA News Today.

Follow the latest developments for all experimental Spinal Muscular Atrophy treatments on the SMA Therapy Tracker.

SMA News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.