Jesy Nelson’s twins and SMA Type 1: everything you’ve asked this week

I picked up Jesy’s Insta story in the last week of the holidays. Asking viewers to stop and watch, she gave a clear update on her baby twins’ condition, although it was one of the most raw and deeply personal I’ve seen in a while. 

Jesy Nelson’s twins have been diagnosed with spinal muscular atrophy (SMA) Type 1. Diagnosis was not straightforward – in fact, their journey began with Jesy’s mum observing lack of lower body movement early on, and a fight for support since. The news immediately sparked concern, curiosity and countless online searches. 

It’s understandable. SMA Type 1 is a condition most people only encounter once it enters their lives directly – through a pregnancy, a newborn, or a family history. While the diagnosis can feel frightening, today’s treatments and support systems offer hope and quality of life that were unimaginable just a decade ago. 

Here, we answer the big, new questions you have about SMA Type 1 – as individuals, parents or parents-to-be – from inheritance and symptoms to treatments, charities and specific resources.

What are the types of SMA?

SMA isn’t one single condition, it exists on a spectrum. Understanding the types can help give some context – here’s a quick outline:

Type 1 (Werdnig-Hoffmann disease)

The most severe form – and the condition affecting Jesy Nelson’s twins – presenting in infancy, often before six months. 

Babies may show muscle weakness, poor head control, feeding difficulties and breathing challenges. Without intervention, SMA Type 1 historically limited life expectancy to early childhood. This is changing, however, with developments in diagnosis and treatment. 

Type 2

Symptoms appear later in infancy or early childhood. Children can sit but may not stand independently. Life expectancy is longer than Type 1 and many live into adulthood with appropriate care.

Type 3 (Kugelberg-Welander disease)

Childhood-onset SMA, milder, with the ability to walk, though mobility may decrease over time.

Type 4

Adult-onset SMA. Muscle weakness is usually mild, and life expectancy is typically normal.

Understanding the type is critical because prognosis, treatment, and daily care differ substantially. For example, SMA Type 1 is life-limiting without treatment, while Type 4 may go unnoticed for years.

What causes SMA Type 1, and is it inherited?

SMA Type 1 is a genetic condition caused by mutations in the SMN1 gene, which produces a protein vital for the survival of motor neurons (the nerve cells that control voluntary muscle movement). Without sufficient SMN protein, motor neurons gradually die, leading to muscle weakness and progressive loss of mobility.

SMA is inherited in an autosomal recessive pattern, meaning that both parents must be carriers of the faulty SMN1 gene. Carriers usually have no symptoms. 

If both parents are carriers, there’s a: 

• 25% chance the baby has SMA
• 50% chance the baby is a carrier
• 25% chance the baby is unaffected

Many families only discover they are carriers during pregnancy or after birth.

How is SMA Type 1 diagnosed?

Early diagnosis is critical.

During pregnancy, SMA can be detected through chorionic villus sampling (CVS) or amniocentesis if the parents are known carriers or there is a family history. Routine ultrasounds cannot detect SMA, although some subtle signs may raise suspicion.

In the UK, newborn screening is being rolled out in several regions, offering the possibility to start treatment before symptoms appear. Detecting SMA early is transformative, as the most effective treatments are gene-targeted and work best before motor neuron loss occurs.

What are the early signs of SMA Type 1 in infants?

Babies with SMA Type 1 usually present symptoms within the first six months of life, including:

• Floppiness or low muscle tone
• Weak or absent head control
• Difficulty swallowing or feeding
• Shallow breathing or reliance on abdominal muscles
• Limited movement in arms and legs

While SMA itself is not painful, secondary complications like joint stiffness, respiratory infections, or fatigue may cause discomfort, which can be managed with multidisciplinary care.

Is SMA Type 1 fatal, and what is life expectancy?

Historically, SMA Type 1 was considered fatal in early childhood. However, the landscape has changed dramatically with gene therapies and SMN-boosting drugs.

• Children receiving early treatment can now survive well beyond infancy, with some reaching school age and adolescence.
• The oldest documented individuals with Type 1 have surpassed previous life expectancy predictions thanks to proactive, comprehensive care. One of the most famous is activist Steve Mikita, who died aged 67 having been diagnosed as a one year-old.

This shift emphasises that SMA Type 1 is now considered a treatable, not untreatable, condition, particularly when diagnosed and managed early.

What treatments are available for SMA Type 1?

Treatment focuses on targeting the genetic root and supporting the body’s function.

Gene therapy

• Onasemnogene abeparvovec (Zolgensma) is a one-off intravenous infusion replacing the faulty SMN1 gene.
• It is most effective when given before symptoms appear.
• Available on the NHS for eligible patients.

SMN-enhancing drugs

• Nusinersen (Spinraza): Spinal injection administered periodically.
• Risdiplam (Evrysdi): Daily oral medication.

Both work to increase SMN protein production, slowing or halting disease progression.

Supportive care

Beyond medication, infants and children benefit from:

• Physiotherapy to maintain movement and prevent contractures
• Respiratory support, including non-invasive ventilation
• Feeding assistance such as nasogastric or gastrostomy tubes
• Specialist equipment for mobility and daily life

A multidisciplinary NHS team typically oversees these interventions, including neurologists, physiotherapists, respiratory specialists and dietitians.

Can SMA Type 1 be cured?

Currently, there is no outright cure, but treatments dramatically alter disease progression, enhance quality of life and extend survival. Early access to gene therapy or SMN-modulating drugs gives families hope where previously there was none.

How does SMA affect families, pregnancy and parenting?

Expectant parents who discover a high risk of SMA may face complex decisions. Genetic counselling, carrier testing and careful pregnancy planning are key resources.

Pregnancy is still possible, but families must plan for delivery, neonatal care and ongoing treatment. High-profile cases like Jesy Nelson’s bring important awareness – they highlight the real-life experiences behind medical facts, and importance of early diagnosis. 

For parents, daily life involves navigating therapies, equipment and potential hospital admissions. It also includes moments of joy, milestones and advocacy, if this feels right.

Resources, charities and blogs

Support extends far beyond the clinic. The UK has a vibrant network of charities and foundations dedicated to SMA:

SMA UK

This is the leading charity for spinal muscular atrophy in the UK. SMA UK offers support for families, advocacy, funding for equipment and awareness campaigns. The Jennifer Trust became SMA Support UK in 2013. 

SMA Foundation (international)

The mission of the Spinal Muscular Atrophy Foundation is to accelerate the development of treatments for SMA. Their focus is research, clinical trials and global advocacy.

August is SMA Awareness Month – make a note and look out for highlights, advances in diagnosis, treatment and research. Efforts by charities, foundations, families, patients and medical teams have helped:

• Push for universal newborn screening
• Fund gene therapy access and clinical trials
• Support family-centred care

Awareness campaigns also educate the public that SMA doesn’t inherently mean a specific life expectancy, or way of life.

Key takeaways

SMA Type 1 is a serious genetic condition, but modern medicine has transformed outcomes. Families now have access to:

• Early diagnosis through prenatal and newborn screening
• Life-changing treatments like gene therapy and SMN-enhancing drugs
• Multidisciplinary physiotherapy, respiratory support, and feeding assistance
• Community support via blogs, social media, charities and patient networks

High-profile stories, like the one unfolding for Jesy Nelson’s twins, shine a spotlight on the challenges and triumphs of living with SMA Type 1, helping raise awareness and encouraging families to seek support as early as possible.

On your reading list: Elsie Hewitt on conceiving with endometriosis – shining a light on a chronically under-diagnosed condition.