US and UK researchers have identified a gene behind a group of rare genetic childhood neurological disorders.
The researchers analysed 75 genes to find the mutation
As well as opening the way for a genetic test, the results could shed light on other neurological conditions.
Children affected with neuroaxonal dystrophies have a build of iron in the brain, which is also found in Alzheimer's and Parkinson's disease.
The study in Nature Genetics found a defect in a specific group of proteins called phospholipases was responsible.
The researchers looked families affected by two of the genetic disorders, infantile neuroaxonal dystrophy (INAD) and neurodegeneration with brain iron accumulation (NBIA).
Both disorders are characterised by an abnormal build-up of iron in the brain which causes the branch-like axons that transmit electrical impulses in nerve cells to swell, interrupting the signal.
Affected children suffer progressive loss of vision, and physical and mental skills.
Working with UK scientists at the University of Birmingham, the researchers collected DNA from 30 to 40 families and narrowed the search for the suspect gene to chromosome 22.
They then looked for genes in the region whose function was suggestive of the symptoms and parts of the body affected by the diseases, and the search was further narrowed to 75 genes.
After scouring the 75 genes, they identified the mutations in PLA2G6, which codes for a protein belonging to a group called phospholipase A2.
When the gene is mutated it alters processes within the cell which leads to a build up of iron, this also is seen in conditions such as Alzheimer's and Parkinson's disease.
There is no cure nor standard treatment for either disease, which are recessive, meaning that both parents must contribute a defective gene to the child. Incidence is one in 500,000 to 1 million.
PLA2G6's discovery means a clinical test can be developed to help families determine their chances of passing the disorders to their children. Study leader Professor Susan Hayflick, professor of molecular and medical genetics, paediatrics and neurology in the Oregon Health and Science School of Medicine said: "There are families who literally are waiting to have this test.
"To have the option of bringing a child into this world you know won't have to suffer like this is extraordinary for a parent who's been through this. Some of them have had multiple children with the disease."
The researchers said they had "unequivocally" linked defects in phospholipase A2 proteins with neurodegeneration.
Professor Hayflick said similar changes in phospholipase A2 metabolism were seen in neurodegeneration associated with ischemia from stroke, spinal cord trauma, head injury and Alzheimer's disease, making it a potential drug target.
And added that iron is known to accumulate with age in brain regions attacked by Alzheimer's and Parkinson's diseases.
"This is a common end effect of many neurodegenerative disorders. To the general population [the discovery] has a larger impact," she said.