Spinal muscular atrophy in children: SMN1, newborn screening and the UK treatment pathway

Motor neurones in the spinal cord carry the signals that tell muscles to contract. They depend on SMN protein to survive. In SMA, both copies of the SMN1 gene are usually faulty, so very little SMN protein is made, and motor neurones are lost. Muscles that no longer receive signals become weak and thin, beginning with the muscles of the trunk and the legs.

A second, almost identical gene called SMN2 makes a small amount of working SMN protein. People inherit varying numbers of SMN2 copies, and MedlinePlus explains that more copies generally mean milder disease. This is why two children with the same SMN1 result can have very different courses, and it is also why SMN2 is the target of some treatments.

The NHS uses age at onset to define types 1 to 4, with type 4 beginning in adult life. MedlinePlus also describes a rare type 0 beginning before birth. In children the picture differs by type:

• Type 1: weakness evident at birth or within a few months, with floppy limbs, weak head control and difficulty with breathing and feeding. It is the most common type, accounting for around half of cases according to MedlinePlus.

• Type 2: weakness emerges in the first year or so. Children can usually sit but do not walk independently. Fine tremor of the fingers, scoliosis and joint contractures are common.

• Type 3: onset after early childhood. Children walk at first, but may need a wheelchair later, and falls, difficulty with stairs and running are early signs.

A baby who is unusually floppy, rarely kicks, has a weak cry or cough, breathes with the tummy moving more than the chest, or has trouble feeding should be assessed urgently. Call NHS 111 for advice or 999 if the baby is struggling to breathe, is blue or grey, or is unresponsive. In an older child, losing a skill such as walking or climbing stairs warrants a GP visit and referral.

SMA is one of the conditions where timing matters, because motor neurones that have already been lost do not regrow. SMA UK makes this point strongly in its advocacy, stating that early diagnosis saves motor neurones that cannot be replaced.

The NHS newborn blood spot test, normally done when the baby is 5 days old, currently lists ten conditions on its public page, and SMA is not among them. SMA UK reports that an in-service evaluation is under way to inform the UK National Screening Committee, with screening in Scotland beginning in March 2026 and a phased rollout in England starting from October 2026 and reaching all thirteen laboratories by October 2027. It reports that Wales and Northern Ireland have no programme yet and that a final screening recommendation is not expected until 2030 to 2031.

These dates come from a charity source and are changing, so families should check current NHS information locally. If a baby has a positive screening result, referral to a specialist neuromuscular centre is arranged quickly for confirmatory genetic testing.

Diagnosis rests on a genetic blood test that looks for loss of SMN1 and counts SMN2 copies. Results guide both the prognosis and the choice of treatment. NHS genetic testing is free when requested by a hospital specialist.

The NHS lists three gene-targeting medicines: nusinersen, risdiplam and onasemnogene abeparvovec. Nusinersen is given by injection into the fluid around the spinal cord, risdiplam is taken by mouth as a liquid, and onasemnogene abeparvovec is a one-time gene therapy infusion for eligible young children. SMA UK says access depends on eligibility criteria, and an intrathecal form of onasemnogene abeparvovec is described as on the path to consideration for use in England. Specialist centres decide which treatment suits which child, and none is described here as a cure.

Medicines work alongside multidisciplinary care. The NHS lists physiotherapy, mobility aids, breathing assistance and dietary changes among supportive measures. In practice that means regular posture and stretching programmes, seating and standing equipment, monitoring of the spine for scoliosis, chest physiotherapy and cough assistance during infections, assessment of swallowing and feeding, and sleep studies when breathing during sleep is a concern.

SMA UK covers practical areas for families of children aged 0 to 12 including equipment, daily life, nursery and school, transport and holidays, and financial benefits. Education health and care plans are one route to the classroom support children may need.