The study authors recommend that all children with the condition should now be genetically tested in response to this surprising new finding.
'Our findings were shocking, actually,' said Dr Stephen Scherer, Director of the Centre for Applied Genomics at The Hospital for Sick Kids in Toronto, Canada, and principal investigator of the study. 'When I showed the results to our clinical geneticists, initially they were floored.'
CP is typically thought to be caused by environmental factors, such as stroke, birth asphyxia (a lack of oxygen to the brain during birth) and infections in the brain of the developing fetus. It is the most common cause of physical disability in children, resulting primarily in problems with motor development, but there is considerable variability in its severity, with some children only mildly affected while others are unable to walk or communicate.
Genetic testing is currently uncommon and is usually only undertaken when other risk factors are absent.
In the study, which was published in Nature Communications, genetic testing was performed on 115 children with CP and their parents, with environmental risk factors previously identified for many of the children. Surprisingly, ten percent of the children studied had a group of clinically relevant genetic changes,called copy number variations (CNV). Some were inherited from their parents, while others were new mutations. These genetic changes are found in less than one percent of the general population.
In five percent of the children with CNVs the genetic changes were small but they affected multiple genes. 'It's a lot like autism, in that many different CNVs affecting different genes are involved, which could possibly explain why the clinical presentations of both these conditions are so diverse,' said Dr Scherer.
In the remaining five percent of children with CNVs the genetic changes were considerably larger. 'For five percent, these big changes are the cause of their CP,' Dr Scherer told CBC News.
The authors are now urging the medical community to consider routinely genetic testing for the diagnostic assessment of children with the condition.
'Finding an underlying cause for a child's disability is an important undertaking in management,' says study co-author Dr Michael Shevell, Pediatrician-in-chief at McGill University Health Centre.
'Parents want to know why their child has particular challenges. Finding a precise reason opens up multiple vistas related to understanding, specific treatment, prevention and rehabilitation. This study will provide the impetus to make genetic testing a standard part of the comprehensive assessment of the child with cerebral palsy.'