The neurological condition robs the body of energy and causes progressive cognitive and physical decline.

Like many parents of children with rare illnesses, mum Louise Gray was anxious to find the source of her baby’s symptoms.

But she said the family ran the gauntlet of medical question marks before the Brisbane toddler’s diagnosis.

That was until a revolutionary blood test which promises to rapidly diagnose thousands of rare diseases came to the family’s aid.

“There’s been 15 reported cases that we’re aware of around the world, and six of those cases are currently alive,” Mrs Gray said.

“It’s given us answers, which is what we didn’t have for so long.”

Ten years in the making, Melbourne researchers claim the development offers “one test to rule them all”.

“Instead of doing a gene-specific test, we can do one test for nearly half of the 7000 rare diseases,” Murdoch Children’s Research Institute professor David Thorburn said.

“We think it will increase the number of diagnoses from the genomic testing from maybe a third to half of all patients, up to around about 70, 75 per cent.”

For families like the Grays, it can also allow earlier access to treatment and eliminate the need for costly and invasive procedures.

“It gives them closure and an end to this question of why, what happened, was it something I did?” University of Melbourne associate professor Dr David Stroud said.

“It can also give the patients access to appropriate treatments and for many families can restore reproductive confidence, allowing them to have a healthy child.”