Spinal Muscular Atrophy (SMA) Type 1 and failures in early diagnosis and treatment

Spinal Muscular Atrophy (SMA) is a rare, inherited neuromuscular disorder that primarily affects the motor neurons in the spinal cord. This genetic condition leads to progressive muscle wasting and weakness, which can in some cases be quite rapid.  

SMA Type 1 is the most severe and common form of SMA, typically showing signs and symptoms within the first six months of life, and quite frequently symptoms are present from birth. It is caused by mutations in the survival motor neuron 1 (SMN1) gene, resulting in a deficiency of the SMN protein necessary for healthy motor neuron function. 

Diagnosing SMA Type 1 begins with recognising clinical symptoms in infants. Babies will be seen in early infancy by a paediatrician (first neonatal check before leaving hospital), by midwives in the community, by health visitors in the community and also General Practitioners for their checks at around 6 weeks of age. 

If SMA Type 1 is suspected a referral to a paediatrician will usually be made. If the family live near a major hospital the baby may be referred directly to a specialist paediatric neurologist for review. The doctor will conduct a thorough medical history and physical examination to assess muscle tone, reflexes, and motor milestones.  

Testing for SMA Type 1 primarily involves genetic testing, which is both highly specific and sensitive. Genetic testing is the definitive method for confirming the diagnosis, as it detects mutations or deletions in the SMN1 gene.  

A blood sample is taken to analyse the presence and function of the SMN1 gene. The absence or mutation of this gene confirms the diagnosis. In some cases, prenatal testing is available for families with a known history of SMA.  

Newborn screening programmes are being increasingly implemented in several countries to enable earlier detection and treatment, however it is not standard practice in the UK currently. Many families (including Jesy Nelson of Little Mix who’s twin daughters were diagnosed with SMA Type 1 in 2025 at 6 months of age) are campaigning for a change in the UK screening system of newborns and there is currently a large study “The Generation Study” being undertaken to assess whether this is feasible and to be recommended in future: The Generation Study: exploring genome sequencing in newborns – UK National Screening Committee 

Early identification of SMA Type 1 is crucial for timely intervention. Parents and healthcare professionals should look out for the following red flag warning signs: 

• Severe muscle weakness, especially in the limbs and trunk 
• Possible history of reduced fetal movements in the womb 
• Poor head control and inability to sit unsupported 
• Floppy or “ragdoll” appearance (hypotonia) 
• Not having a startle reflex to the “drop test” 
• Difficulty swallowing, poor feeding, or suck 
• Weak cry or cough 
• Shallow or rapid breathing 
• Lack of normal reflexes 

If any of these symptoms are observed in an infant, urgent medical evaluation is recommended. 

While there is currently no cure for SMA Type 1, significant advances have been made in its management. Treatment aims to improve quality of life, extend survival, and manage symptoms. Key treatment options include: 

• Gene Therapy: Onasemnogene abeparvovec (Zolgensma) delivers a functional copy of the SMN1 gene. It is administered as a one-time intravenous infusion. 
• SMN2 Splicing Modifiers: Nusinersen (Spinraza) and risdiplam (Evrysdi) increase production of SMN protein from the backup SMN2 gene. 
• Supportive Care: Includes respiratory support, nutritional management, physiotherapy, and occupational therapy to address complications and maintain function. 

Early initiation of these treatments, especially before significant muscle loss occurs, is associated with improved outcomes. Once muscle damage and loss occurs it is not reversable and can cause long term and significant disabilities. Many children lose the ability to walk and are wheelchair dependent.  

Missed or delayed diagnosis of SMA Type 1 can have serious consequences. Early symptoms may be subtle or mistaken for other conditions, resulting in many infants not getting timely intervention and treatment. Many parents report raising concerns multiple times with medical staff, only to be reassured or dismissed.  

Failure to intervene at an early stage can lead to rapid progression of muscle weakness, respiratory failure, and a reduced chance of benefiting from disease-modifying therapies.  

In publicity raised by Jesy Nelson, she described that the diagnosis of her twins’ condition was not made until they were 6 months of age, despite her taking them to her GP and health visitors with repeated concerns. Jesy had taken the twins to her GP 3 times with concerns about their feeding, but was reassured all was well. It was only when her mother pointed out that the movement of their legs did not appear normal that medical staff reacted. 

Increased awareness among healthcare providers and parents, as well as the expansion of newborn screening, are critical strategies to prevent missed diagnoses. 

Understanding the signs and treatment options for SMA Type 1 is vital for improving the lives of affected children. Early detection and intervention can make a really significant difference, underscoring the importance of awareness and for wider early genetic screening. 

If you have concerns about the late diagnosis of your child’s SMA Type 1 it is important to consult a specialist solicitor with experience in investigating claims relating to the late diagnosis of genetic conditions.