Two children with a rare genetic condition will live very different lives because one was tested at birth and the other was not, their parents say.

Marley, five, and Meadow, four months, both have spinal muscular atrophy (SMA), a progressive muscle-wasting disease that can cause death within two years if untreated.

But while Marley, who was diagnosed at five months, cannot walk or talk and needs help to breathe, Meadow is meeting all the milestones for her age after she was tested at birth and received life-changing gene therapy at the earliest opportunity.

Their parents Rosie and Wes, from Driffield, East Yorkshire, are calling for all babies to be screened for the condition.

“The earlier you find out about newborn SMA, the earlier your life turns around,” Rosie says.

“Marley has complex needs and needs full daily life attention. Meadow is going to live a completely normal life and will barely need any breathing support.”

The couple are backing a campaign by the charity SMA UK, which wants the disease to be added to a blood spot test that already checks newborn babies for 10 rare but serious conditions.

At present, screening for SMA is only carried out on those who have a sibling with the condition.

According to the charity, an estimated 47 babies were born with the condition in the UK in 2024, though about 1 in 40 people carry the altered gene that can cause the disease.

Rosie and Wes say their world came “crashing down” when Marley was diagnosed with SMA at the age of five months.

“Marley has to have respiratory support every single day,” Rosie says. “He cannot eat orally so he’s fed via a tube.

“He has a ventilator at night-time. He can’t walk or talk.”

Marley was given Zolgensma, a life-changing gene therapy drug, at 16 months.

According to SMA UK, the drug delivers a healthy copy of the affected gene to the body, but timing is critical because irreversible damage may have already occurred in the nervous system.

Rosie and Wes say this means early detection of SMA is crucial for giving children the greatest quality of life possible.

The drug was given to Meadow within a few weeks of her birth.

For Rosie, hearing her daughter’s diagnosis “was a very hard pill to swallow”. But she is now hitting her developmental milestones.

“She is already rolling over back to front and front to back at four months old,” Rosie says.

In 2018, the UK National Screening Committee (NSC) recommended against screening for SMA, citing limited evidence of long-term treatment outcomes and cost-effectiveness for the NHS.

However, over the past few years it has carried out a review of the decision because of “significant developments”, including new drugs. Further evaluation work is due to be carried out within the NHS.

Meanwhile, testing for all babies is due to begin in Scotland in 2026 under a two-year pilot programme.

Portia Thorman, from SMA UK, believes it would be ”ethically wrong” not to introduce screening throughout the UK.

“I think facing a diagnosis now, you can be filled with hope,” she says.

“Children are getting diagnosed much earlier than they used to be and there are three brilliant drugs that work incredibly well. The future for these children is bright.”

Laurent Servais, a professor of neuromuscular diseases at the University of Oxford, carried out a study of newborn screening based on programmes in other countries, such as Belgium.

“In the US, in Europe, in Japan, in Australia, every single baby is screened at birth for SMA, even if there is no case in your family”, he says.

A similar approach in the UK would mean children could be “treated immediately, giving them a completely different future”.

Prof Servais argues newborn testing is “extremely easy to implement” and the effectiveness of the treatment would outweigh the cost of screening.

A spokesperson for the Department of Health and Social Care said: “The UK National Screening Committee has recommended a large-scale study for spinal muscular atrophy screening in newborns to gather further evidence.

“This is under consideration and we are working closely with families and campaigners as part of this.”

Though Marley was not diagnosed at birth, his parents say he has made incredible progress due to drugs and physiotherapy.

“He’s been doing really, really well. He couldn’t sit up unaided when he first came here [to therapy], but now he can sit up unaided for three minutes,” says Rosie.

Marley has also started at mainstream school and can “sit up in class in his chair and be like the other kids”.

However, Rosie and Wes know Meadow’s early test means her life is likely to be very different to Marley’s.

“I think the guilt that eats me and my partner up, as well as other families of SMA, is massive,” Rosie says.

But she adds: “If you’ve had a child that’s been diagnosed with SMA, it gets better”.