SMA explained: The rare genetic condition affecting Jesy Nelson's twins

Former Little Mix singer Jesy Nelson has said her twin babies are unlikely to ever be able to walk after being diagnosed with a rare condition.

The 34-year-old, who gave birth prematurely to Ocean Jade and Story Monroe Nelson-Foster in May with her fiancé, Zion Foster, said the twins have been diagnosed with type 1 spinal muscular atrophy (SMA).

In an Instagram video post on Sunday, she said: “We were told that they’re probably never going to be able to walk, they probably will never regain their neck strength, so they will be disabled, and so the best thing we can do right now is to get them treatment, and then just hope for the best.”

But what is SMA, and what does treatment for the condition look like? ITV News explains.

What is SMA?

Spinal muscular atrophy (SMA) is a rare genetic condition that causes muscle weakness, according to the NHS.

It gets worse over time, but medicines and other treatments can help manage symptoms.

What are the different types of SMA?

SMA is usually grouped into four main types, based on what age the symptoms begin and how they affect sitting, standing and walking.

Type 1: Babies under six months
Type 2: Babies and toddlers aged six to 17 months
Type 3: Children and teenagers from 18 months to 17 years
Type 4: Adults aged 18 and over

What causes SMA?

Most types of SMA are caused by an altered gene called SMN1, which is passed on to a child by their parents.

The parents usually do not have SMA themselves, and in most cases, SMA can only be passed on if both parents carry the altered gene.

Parents usually do not have SMA themselves but carry the altered gene.

If both parents are carriers, there is:

A one in four (25%) chance that a child will have SMA
A one in two (50%) chance that the child will carry the altered gene, but will not have SMA
A one in four (25%) chance that the child will neither have SMA nor carry the gene

How does SMA affect people’s livelihoods?

The NHS says SMA affects everyone differently. Some types are more severe and can affect life expectancy.

In general, the earlier symptoms begin, the more serious the condition is likely to be, though outcomes depend on individual symptoms and how well treatment works.

How is SMA diagnosed?

If a doctor suspects a child may have SMA, the condition can be confirmed with a blood test, according to the NHS.

People who may be at risk of having a child with SMA can be referred by their GP to a genetic counsellor to discuss risks and options.

Tests are available before, during and after pregnancy. These include:

A genetic blood test to check whether someone carries the altered gene
Chorionic villus sampling (CVS) or amniocentesis during pregnancy to see if a baby has SMA
A blood test after birth to confirm a diagnosis

In early 2026, Scotland will become the first part of the UK to routinely screen newborns for SMA.

The scheme is a two-year pilot, funded by the Scottish Government and pharmaceutical company Novartis, that will see infants born in Scotland screened for the condition as part of the existing blood spot test when they are just five days old.

Countries including France, Germany, Russia, Norway, Sweden and Turkey have already introduced nationwide SMA blood spot testing for newborns.

Five-year-old Edward Willis-Hall was given the new gene therapy Zolgensma, which costs £1.79m, to treat SMA, as Good Morning Britain reports

What treatments are available for SMA?

There is currently no cure for SMA, but treatments and support are available to help improve quality of life.

Care is usually provided by a team of specialists who create an individual care plan.

The main treatments include medicines that target the genetic cause of SMA, such as:

Nusinersen (Spinraza)
Risdiplam (Evrysdi)
Onasemnogene abeparvovec (Zolgensma)

Not everyone with SMA is eligible for these medicines. The most suitable treatment depends on age, symptoms and overall health, and doctors will discuss the potential benefits and risks.

Research into new treatments for SMA is ongoing.