What Is SMA Type 1 and Could It Affect You? Jesy Nelson's Twin Daughters Were Just Diagnosed With It

Spinal muscular atrophy is a rare genetic condition that quietly damages the body's ability to move, and it has entered public focus after Jesy Nelson revealed her newborn twins have been diagnosed with it.

Jesy Nelson is a British singer and television personality, best known as a former member of the girl group Little Mix. She rose to fame after the group won The X Factor in 2011 and went on to achieve multiple UK number-one singles. Nelson left Little Mix in December 2020, citing mental health reasons, and later launched a solo music career. She has spoken publicly about body image, online abuse, and her experiences in the music industry. While she has been in headlines recently for her twins' birth, she has once again been thrust into the spotlight after sharing a video where she talks about their diagnosis: Spinal Muscular Atrophy.

Spinal muscular atrophy, commonly known as SMA, is a group of inherited neuromuscular disorders that cause muscle weakness and wasting over time. The condition affects lower motor neurons in the spinal cord, which are responsible for sending signals that allow muscles to move. When these nerve cells die, muscles no longer receive instructions, leading to progressive weakness.

The weakness tends to be most severe in muscles closest to the centre of the body, including those that control the head, neck, chest, and legs. As the condition progresses, everyday movements such as sitting, swallowing, and breathing can become difficult. There is no cure, but treatment can help manage symptoms and slow progression.

The Different Types Of SMA

There are five recognised subtypes of SMA, classified by age of onset and severity. SMA type 0 is the rarest and most severe, affecting babies before birth and often leading to death within the first month of life. SMA type 1, also known as Werdnig-Hoffman disease, accounts for around 60 per cent of cases and usually appears within the first six months.

Children with SMA type 1 experience severe muscle weakness, difficulty swallowing, and breathing problems. Without breathing support, life expectancy is usually under two years. SMA type 2 appears between six and 18 months, with children often able to sit but not walk, while SMA types 3 and 4 are milder and usually do not affect life expectancy.

How Common Is The Condition?

Although considered rare, SMA is one of the most common severe inherited conditions in infancy and childhood. It affects an estimated one in 6,000 to one in 11,000 live births. The condition is about twice as common in white and Asian populations as in Black and Hispanic populations.

SMA is inherited in an 'autosomal recessive pattern', which means that both biological parents must carry a mutated SMN1 gene. Most carriers do not have symptoms, and among white populations, around one in 50 people carry the gene. In rare cases, the mutation can arise during early development.

All types of SMA are caused by mutations in the SMN1 gene, which is responsible for producing a protein vital for motor neuron survival. Without enough of this protein, motor neurons shrink and die, preventing the brain from controlling voluntary muscle movement. The severity of the condition depends partly on the number of copies of a backup gene, SMN2, that a person has.

The SMN2 gene produces small amounts of the same protein, and having more copies can lessen symptoms. This explains why some people develop mild weakness in adulthood, while others show severe symptoms in infancy. Genetic testing can confirm SMA in around 95 per cent of cases.

Jesy Nelson's Daughters And SMA Type 1

Nelson revealed that her twin daughters, Ocean Jade and Story Monroe Nelson-Foster, have been diagnosed with SMA type 1. Speaking in an Instagram video, she said the girls were not moving their legs as expected and were struggling to feed. After months of medical appointments, they were assessed at Great Ormond Street Hospital in London.

Nelson said doctors told her the twins would 'probably never be able to walk' and would likely not regain neck strength. She explained that SMA 'does affect every muscle in the body, down to legs, arms, breathing, swallowing'. The twins have since received treatment, which Nelson said was essential, adding, 'Because if they don't have it, they will die.'

Diagnosis And Treatment Options

SMA is usually diagnosed through genetic testing, often after physical and neurological examinations. In some countries, newborn screening is routine, allowing treatment to begin before symptoms appear. Prenatal testing is also possible during pregnancy through procedures such as amniocentesis or chorionic villus sampling.

Treatment focuses on managing symptoms and preventing complications. This includes physical and occupational therapy, breathing support, feeding assistance, and medications that increase SMN protein production. In recent years, gene replacement therapy and disease-modifying drugs have significantly improved survival, particularly for babies with SMA type 1.

Could SMA Affect You?

Because SMA is inherited, anyone can be a carrier without knowing it. Carrier testing can determine whether you or your partner carries the altered gene. Genetic counselling can then explain the likelihood of having a child affected by SMA and help potential parents discuss options before pregnancy.

Nelson said she shared her daughters' diagnosis to raise awareness and encourage faster diagnosis. 'The last three months have honestly been the most heartbreaking time of my life,' she said, while adding she believes her daughters will 'defy all the odds' with the right care.