Genetic screening has revealed a little girl was misdiagnosed with a life-limiting illness and instead has a condition which only affects a handful of children across the UK.

Addison Black, five, from Wallsend, North Tyneside, was first thought to have Joubert syndrome, a brain development disorder, but experts from Newcastle University have given her family hope after diagnosing Poretti-Boltshauser syndrome (PBS), which is rarer and milder.

Her family is one of four across the UK who have had a diagnosis changed from Joubert to PBS, following an expert review of symptoms, brain scans and genetic sequencing.

PBS is so new that one of the experts it is named after, Professor Eugen Boltshauser, is still working.

A key feature of Poretti-Boltshauser is that it is non-progressive and does not lead to kidney failure and other life-threatening complications associated with other brain diseases such as Joubert syndrome.

The findings are important for the NHS as genome sequencing is becoming mainstream so this rare disorder can be identified quickly if considered alongside other diseases with similar characteristics.

Professor John Sayer, deputy dean of clinical medicine at Newcastle University, said: “Our study shows that by carefully re-evaluating children with a clinical label of Joubert syndrome, we were able to make both a clinical and genetic diagnosis of a much rarer, but milder, syndrome called Poretti-Boltshauser.

“Our study revealed that children with congenital brain disorders may have a delayed or incorrect diagnosis due to poor recognition of key features on brain imaging and incomplete genetic testing.”

Addison’s parents Carli and Stewart Black were shocked when her diagnosis changed, and their relief was tinged with worry about the unknown future PBS could bring.

Mrs Black, a former nurse, said: “When your child has complex needs then your whole life understandably revolves around them and making sure they’re OK and have the best treatment possible.

“We knew from a very young age that something was not right with Addison’s development as she wasn’t hitting the milestones – she couldn’t make eye contact, had head twitching and didn’t walk until after the age of three.