April 13 (HealthDay News) -- New research suggests that muscle weakness in a child with autism may point to an underlying genetic defect that's causing mitochondrial disease, which means the muscles don't get the energy they need.

Conversely, it's possible that the mitochondrial disease may also play a role in the development of autism, perhaps by preventing the brain from getting the energy it needs to perform properly, the researchers noted.

"In large studies of kids with autism, about 20 percent have markers of mitochondrial disease in the blood," explained Dr. John Shoffner, an associate professor of biology at Georgia State University and president of Medical Neurogenetics.

Shoffner recently completely a retrospective analysis of 37 children with autism spectrum disorders and found that 65 percent of these children -- children who had been referred to him because their doctors suspected additional problems -- had mitochondrial defects.

He was expected to present the findings April 13 at the American Academy of Neurology's annual meeting, in Chicago.

Mitochondria are found in every cell of the body, with the exception of red blood cells, according to the United Mitochondrial Disease Foundation (UMDF). Mitochondria are vital to survival, because they make oxygen available to cells and metabolize food into energy for cells to thrive. Defects in mitochondria can lead to cell injury, or even cell death, according to UMDF.

Symptoms of mitochondrial disease depend on which body system is affected but may include muscle weakness, loss of muscle control, poor growth, heart disease, diabetes, developmental delays, an increased risk of infection and more.

Shoffner said that the mitochondrial energy production system is the only one in the body that requires two genomes to work -- genes inherited from both the mother and the father, and genes exclusively from the mother. "To make this system work, it requires a lot of genes. Hence the opportunity for lots of problems," said Shoffner, who added that there are several hundred known mitochondrial disorders.

Twenty-four (65 percent) of the children included in this study had genetic defects in their skeletal muscles. However, that doesn't mean that 65 percent of children with autism likely have mitochondrial disease. This was a select population of kids with autism, ones that had specifically been referred, because their doctors suspected a problem.

But, Shoffner pointed out that as many as one in five youngsters with autism spectrum disorders have shown signs of mitochondrial disease.

"If you're talking about 20 percent of kids with autism, that's a whole lot of children, and may represent an important segment of the autism spectrum disorder population. And we may be getting a foothold into the underlying cause of autism spectrum disorders," he said, adding, "This is a really important step forward that lets us put effort into understanding the mechanisms of disease."

"This study is a call to action. We need to know what is the real prevalence of mitochondrial conditions in children with autism," said Geraldine Dawson, chief science officer for Autism Speaks. "The more we can identify these subgroups of kids, the more we're going to parse apart the many forms of autism. This gives us clues to etiology."

"If we find that mitochondrial disease is a prevalent condition, having a better understanding of the kinds of symptoms that children may show if they have it might be helpful for parents," she said.

Shoffner said these findings may also open up new avenues of research into potentially more effective treatments for the future.

SOURCES: John M. Shoffner, M.D., associate professor, biology, Georgia State University, and president, Medical Neurogenetics, Atlanta; Geraldine Dawson, Ph.D., chief science officer, Autism Speaks; April 13, 2008, presentation, American Academy of Neurology annual meeting, Chicago