Type 3

This information sheet briefly explains the cause, effects, and management of Spinal Muscular Atrophy (SMA) Type 3. It includes sources of further information and support. It is written for the families of children diagnosed with SMA Type 3. It may also be useful for healthcare and other professionals.

SMA Type 3 is a complex condition; there is a lot of information to take in, and every child with SMA is different. Your child’s medical team will always be happy to go over any of this with you.

What is SMA Type 3?

SMA Type 3 is sometimes called Kugelberg-Welander disease. The symptoms of muscle weakness and floppiness (low tone / hypotonia) usually appear after 18 months of age but the actual age of onset is very variable and may not appear until late childhood or early adulthood.

Each child with SMA Type 3 is different but the onset of muscle weakness is gradual and children are generally able to walk until late childhood and sometimes into adolescence3.

Sometimes doctors try to indicate the degree of severity within SMA Type 3 by using a decimal classification4, for example, 3.1, 3.2, 3.5, 3.9. If you have any queries regarding this please speak to your child’s medical team.

Life expectancy for children diagnosed with SMA Type 3 is usually normal5 and most people live long, fulfilling, and productive lives.

How is SMA Type 3 diagnosed?

A doctor will diagnose SMA Type 3 after taking a medical history, physically examining your child, and by taking a blood sample for DNA testing. The blood sample is tested for a deletion mutation in the survival motor neurone 1 (SMN1) gene on chromosome 5. The result of this test is usually available within 2 – 4 weeks.

There may be uncertainty about the diagnosis, so further observations and muscle tests such as an electromyogram (EMG) or a muscle biopsy may be needed, which can take time.

Is there a treatment or cure for SMA Type 3?

There is one approved treatment for SMA, Spinraza™. Its availability varies from country to country and SMA Types. If Spinraza™ is not available in your country, symptoms can be managed so that your child can achieve their maximum mobility, independence, and quality of life.

What are the effects of SMA Type 3?

This section describes the effects of SMA Type 3 in general terms. But, it’s important to remember that each child with SMA Type 3 is affected differently and the severity of the condition varies from child to child.

Children’s muscle weakness is usually the same on both sides of their body (symmetrical). The muscles closest to the centre of their body (proximal muscles) are usually more severely affected than the muscles furthest from the centre of their body (distal muscles). Generally, children with SMA Type 3 find that their legs are weaker than their arms.

As your child grows, it may be difficult for their muscles to keep up with their daily activities. If your child has been able to, for example, walk or climb stairs, they may lose this ability as they get older. Some children may fall more easily as a result of their muscle weakness. If they are sitting on the floor they may need help getting up. About 50% of children with SMA Type 3 will lose the ability to walk independently by the age of 146 although some people are still able to walk in adulthood.

In SMA Type 3 the muscles supporting the spinal column are weakened. This means that some children will develop a sideways curvature of their spine6 (scoliosis). Also, because the condition reduces children’s ability to move, some joints may become tight (contractures) restricting their range of movement.

Muscle weakness in children with SMA Type 3 mainly affects their limb movement. It doesn’t affect bladder and bowel control but some children may need help with toileting, dressing, and undressing.

Children with SMA Type 3 may become weaker after infections and at times of major growth spurts such as puberty. SMA doesn’t affect a child’s sexual or intellectual5 development.

What healthcare and support is needed for SMA Type 3?

Your child should receive care from a multidisciplinary healthcare team, which can feel like a lot of people, but they all have an important role to play. You may have contact with specialists in some of the following areas: neuromuscular conditions; respiratory medicine; orthopaedics; physiotherapy; occupational therapy; speech and language therapy; dietetics; and a hospital or community consultant paediatrician. If possible one of the team should be your keyworker whose job it is to help co-ordinate services for your family.

Children with SMA Type 3 should be seen by their medical team regularly to measure any change in their health and to offer advice and interventions at the right time. The aim is to enable your child to remain healthy and enjoy a good quality of life.

At every appointment with your child’s medical team you should be given time to ask questions and then jointly decide what support is best for your child.

Children with SMA Type 3 do not generally have difficulties with their breathing, but their breathing strength and cough effectiveness should be checked regularly.

You can read an overview of what good respiratory management involves in the booklet ‘Standards of Care for Spinal MuscularAtrophy – the family guide’7. As each child with SMA Type 3 is affected differently it’s important to discuss any queries you have with your child’s medical team.

A healthy diet is important for everyone. Your child’s health visitor and consultant will be able to provide advice and support on eating and nutrition.

Your child may become overweight if they have reduced mobility. If this happens the extra weight can increase the stress on muscles, bones and joints, making physical activity even more difficult. If needed, a dietician will be able to advise on a healthy diet that will suit your child.

Children with SMA Type 3 rarely have difficulty with their chewing and swallowing but your child’s medical team will provide you with advice and support if necessary.

Children with SMA Type 3 can become constipated which may cause discomfort. You can discuss how to manage this with your child’s medical team.

Children with SMA Type 3 have difficulties with their posture, movement, and mobility. Each child needs their own exercise routines designed by their physiotherapist to help with this. Routines may include exercises to help maintain their range of motion, reduce any discomfort, stretch any tight muscles, and prevent contractures. Regular, gentle stretching of their tight joints can help to reduce the pain that contractures can cause. If your child does have any pain, do talk to their doctor and physiotherapist. Your child might enjoy doing these exercises in the bath, or a swimming or hydrotherapy pool as the warm water aids buoyancy.

Regular, moderate exercise will also help your child to maintain their fitness and stamina and activities such as swimming and horse riding can be adapted to match their physical ability.

Although your child will lose muscle strength over time, it is important that they maintain activities like standing and walking for as long as possible. Walking can help delay the development of scoliosis3 and standing is good for breathing, blood circulation, bladder, bowels, bones and joints.

As your child’s physical abilities change, an occupational therapist will advise what sort of seating will give them the best, most comfortable support. This will make it easier for them to play with toys, eat independently, and join in at home and at school.

A physiotherapist will assess your child and provide appropriate equipment to support their standing, walking and positioning. Some children with SMA Type 3 benefit from having splints (sometimes called orthoses) for support with standing and walking. Types of orthoses include ankle foot orthoses (AFOs) and knee, ankle, footorthoses (KAFOs). These will be made specifically for your child by an orthotist who will explain how they will help.

Specialist equipment will enable your child to participate in activities both at home and at school. If your child finds walking increasingly difficult or they are having falls then they may benefit from using a walking frame or a manual wheelchair.  If your child’s weakness increases, a powered (electric) wheelchair may help their independence. Your child’s physiotherapist and occupational therapist will be able to advise you about walking aids and wheelchairs.

As already mentioned, children with SMA Type 3 may develop a sideways curvature of their spine (scoliosis). It is important that the medical team monitors your child regularly so that any increase in curvature is noticed early. This is more likely to develop if your child is no longer able to walk3. The degree of the curvature and your child’s age will be factors in deciding how to manage this. Initially this may be with a spinal brace or jacket but surgery to correct scoliosis may be recommended if the scoliosis is contributing to breathing difficulties, is preventing comfortable sitting, or if the curvature has progressed beyond a certain point.

Occupational therapists can give you advice about other adaptations and equipment that will help with your child’s everyday activities such as writing, playing, washing, dressing, cooking and eating, both at home and at school. With appropriate encouragement, adaptations, and support, your child will be able to lead as fulfilling a life as their friends.

What other help is available?

A diagnosis of SMA Type 3 with all its complexity can have an enormous impact on families. It’s important for you and your child to have emotional support and plenty of time to talk and ask questions. This can be with members of your child’s medical team, your local G.P., health visitor, social worker, psychologist or a counsellor.

To enable your child to participate fully in activities at home, school, and in their community, you will need information, advice and support on mobility, education, equipment and sources of funding that will aid their inclusion.

As a parent with a child with SMA you should be offered a referral forgenetic counselling to help you understand how SMA is passed on and what the chances are of other people in your family being affected. Genetic counselling also provides you with the opportunity to discuss your choices for any future pregnancies.

As your child and any siblings grow up, they can also ask for genetic counselling, particularly if they are considering having children.

For more information on the genetics of SMA, the chances of having a child with SMA and the tests that can be carried out, please see ourGenetics of Spinal Muscular Atrophy leaflet.


  1. Lunn, M.R. and Wang, C.H. (2008) ‘Spinal muscular atrophy’,The Lancet, 371(9630), pp. 2120-2133.
  2. Lefebvre, S., Bürglen, L., Reboullet, S., Clermont, O., Burlet, P., Viollet, L., Benichou, B., Cruaud, C., Millasseau, P., Zeviani, M., Le Paslier, D., Frézal, J., Cohen, D., Weissenbach, J., Munnich, A. and Melki, J. (1995) ‘Identification and characterization of aspinal muscular atrophy-determining gene’, Cell, 80(1), pp. 155-165.
  3. Tsirikos, A.I. and Baker, A.D.L. (2006) ‘Spinal muscular atrophy: classification, aetiology, and treatment of spinal deformity in children and adolescents’, Current Orthopaedics, 20(6), pp. 430-445.
  4. Dubowitz, V. (1999) ‘Very severe spinal muscular atrophy (SMA Type 0): an expanding clinical phenotype’, European Journal Paediatric Neurology, 3(2), pp. 49-51.
  5. Montes, J., Gordon, A.M., Pandya, S., De Vivo, D.C. and Kaufmann, P. (2009) ‘Clinical outcome measures in spinalmuscular atrophy’, Journal of Child Neurology, 24(8), pp. 968-978.
  6. Mercuri, E., Bertini, E. and Iannacconne, S. (2012) ‘Childhood spinal muscular atrophy: controversies and challenges’ The Lancet Neurology, 11(5), pp. 443-452.
  7. TREAT-NMD Neuromuscular Network (2008) Standards of Care for Spinal Muscular Atrophy. Available here.
  8. Commission of the European Communities (2008)Communication from the Commission to the European Parliament, the Council, the European Economic and Social Committee and the Committee to the Regions on Rare Diseases: Europe’s challenges. Available here.