This information sheet briefly explains the cause, effects, and management of spinal muscular atrophy (SMA) Type 1. It includes sources of further information and support. It is for the families of children diagnosed with SMA Type 1. It may also be useful for healthcare and other professionals.
SMA Type 1 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.
SMA Type 1 is the most severe form of SMA. It accounts for between 50 – 70% of cases of childhood onset SMA. It is sometimes called Werdnig-Hoffmann disease or severe infantile SMA.
Each baby with SMA Type 1 is different. The symptoms of SMA Type 1 usually appear within the first few months of life. In some cases SMA can affect babies even before birth and mothers may remember that their baby had become less active towards the end of their pregnancy. Generally, the earlier the onset of symptoms, the more severe the condition. Unless treated, the most severely affected babies may die before, during, or very shortly after birth. This is sometimes referred to as SMA Type 0.
Sometimes doctors try to indicate the degree of severity within SMA Type 1 by using a decimal classification3, for example, 1.1, 1.2, 1.5, 1.9. If you have any queries regarding this please speak to your child’s medical team.
SMA Type 1 is a life-limiting condition. Though it is not possible to accurately predict, for the majority of children (approximately 95%) life expectancy is less than 18 months unless pharmacological treatment is introduced. In general, unless started on one of the approved pharmacological treatments, babies diagnosed within the first few weeks or months of life have a significantly shorter life expectancy.
If a doctor suspects SMA after taking a medical history and physically examining a baby, the diagnosis is confirmed by taking a blood sample for DNA testing. The blood sample is tested for a deletion in the survival motor neurone 1 (SMN1) gene on chromosome 5. The result of the test is usually available within 2 – 4 weeks.
Further tests, such as an electromyogram (EMG) or muscle biopsy, may be considered if there is any uncertainty about the diagnosis, but are not usually needed to confirm SMA.
Babies with SMA Type 1 are often described as ‘floppy’ babies, due to their low muscle tone (hypotonia) and severe muscle weakness. The muscle weakness affects movement, swallowing and breathing. Babies with SMA Type 1 are unable to lift their heads, have difficulty rolling over and are unable to sit unsupported. They may also have a weak cry.
In SMA, muscle weakness is usually symmetrical. The muscles close to the centre of the body (proximal muscles) are usually affected more severely than the muscles situated away from the centre of the body (distal muscles) and the legs are generally weaker than the arms. This results in babies having difficulty lifting their arms and legs, while still being able to use their hands and fingers.
The brain is unaffected and babies affected by SMA are often described as bright, alert and responsive. The muscles of the face are not usually affected so babies can smile and frown.
Weakness of the respiratory muscles can cause severe difficulties with breathing and coughing. It can also increase susceptibility to respiratory viruses and infections which can be life-threatening.
The muscles used for sucking and swallowing are also affected and this may cause difficulty with feeding and weight gain. Difficulty with swallowing can increase the risk of fluids, or food, passing into the lungs (aspiration) which can cause choking and, in some cases, pneumonia.
At present there are three approved treatments for SMA: nusinersen (Spinraza®), onasemnogene abeparvovec (Zolgensma®), and risdiplam (Evrysdi™). Their availability varies from country to country. There is also a range of options aimed at managing symptoms, reducing complications of weakness and maintaining the best quality of life for as long as possible.
A baby with SMA Type 1 should receive care from a multidisciplinary team which may include specialists in neuromuscular conditions, palliative care, respiratory medicine, physiotherapy, occupational therapy, speech and language therapy, dietetics and a hospital or community consultant paediatrician. Where available, a key worker should assist in the co-ordination of services for the family.
The impact of a diagnosis of SMA Type 1 on families is enormous. Parents should be offered ongoing support with emotional, practical and financial issues following the diagnosis of their baby.
Parents should also be offered a referral for genetic counselling to help understand how SMA is passed on and the chances of other children being affected. Genetic counselling also provides the opportunity to discuss choices for future pregnancies.
Good respiratory management is important to provide comfort and reduce complications of muscle weakness. An overview of respiratory management in SMA can be found in the booklet ‘Standards of Care for Spinal Muscular Atrophy – the family guide’ published by TREAT-NMD. This booklet can be obtained from the TREAT-NMD website.
There are a number of options for respiratory support. Not all options will be appropriate for all babies with SMA Type 1.
The options may include:
Choosing the most appropriate management involves very difficult decisions. Parents should have time and support to ask questions and discuss the different options, to help decide which is most appropriate for their baby. These discussions will be with the medical team who has knowledge of their baby’s condition and possible progression. Parents may also wish to seek emotional support from sources outside the medical team e.g. their family, community and spiritual leaders.
Babies with SMA Type 1 may encounter problems with feeding and swallowing due to muscle weakness. Feeding can become a tiring process for babies with SMA Type 1 and as a result they may lose weight. Babies with a weak swallow are also at risk of inhaling (aspirating) their feed which can cause chest infections.
Advice and support on feeding, swallowing and diet is available to parents from a number of healthcare professionals. These may include the health visitor at their local health centre, the child’s consultant, speech and language therapist, dietitian and community nurse. Occupational therapists and physiotherapists may also advise on positioning and seating which may assist feeding.
At this time there is no clear evidence that babies with SMA Type 1 need a therapeutic feed or one with an increase or decrease in particular nutrients.
If swallowing becomes unsafe, or if a baby is not gaining enough weight, alternative ways of feeding may be suggested. These may include feeding through a nasogastric (NG) tube, a nasojejunal (NJ) tube or a gastrostomy (G) tube.
Parents should have the opportunity to discuss the reasons for these suggestions and have time to ask questions, so they understand the possible benefits and risks to their baby. Whichever option is chosen, parents will be provided with training and support to enable them to feed their child safely at home.
Constipation is a common problem with babies with SMA Type 1. It can cause discomfort and respiratory distress. Some babies may also experience reflux. To reduce discomfort and prevent complications, the management of these symptoms should be discussed with the baby’s medical team.
Parents should have the opportunity to discuss the range of care options in depth with their baby’s medical team to decide what support is most appropriate for their individual circumstances. These discussions are important for developing an anticipatory care plan, which records the treatment parents wish their baby to receive when his/her health deteriorates or in an emergency situation. This plan can be reviewed and parents can change their minds at any time.
Ideally the goal of care is to enable a child to enjoy a good quality of life at home with their family for as long as possible, with a minimum of hospital admissions.
In addition to medical interventions available for breathing and feeding, additional support is available to improve a baby’s health and wellbeing and to provide emotional support for the family. When a baby is at home this may be provided by their GP, community nursing or palliative care team. Children’s hospices also offer a wide range of services and support to children with life-limiting conditions and their families.
Physiotherapy can provide passive exercises to enable movement that babies are unable to make independently. Parents can be taught these techniques so they can enjoy doing these with their baby at home between appointments. Passive exercises are also good for babies’ circulation and help prevent stiffening of the joints (contractures).
Physiotherapists may suggest performing stretches and exercises when a baby is in the bath, swimming or hydrotherapy pool. Building these exercises into play can make them fun and babies enjoy the additional freedom of movement provided by warm water.
Chest physiotherapy is also very important to help clear the chest when babies have difficulty coughing.
Good posture management can improve comfort. An occupational therapist can advise on seating which will help to provide appropriate support for babies with low muscle tone. This will also make it easier for them to play.
Sleep systems may sometimes be provided to increase comfort and support a baby’s limbs in a good position at night time.
Other sources used: