Q:What does the case mean for the safety of vaccines?

Medical experts said parents should continue vaccinating their children because it protects them from diseases known to be deadly. If they're concerned, they should talk with their pediatrician.

Q: What is autism?

A: Autism spectrum disorders are a range of developmental disabilities — from mild to severe — characterized by communication problems, an inability to have normal social interactions and unusual behaviors.

Q: What causes autism?

A: Scientists don't know but are exploring what role genetics may play, as well as possible environmental factors.

Q: Why is this Georgia child's case drawing so much attention?

A: A leaked federal vaccine court document, posted on the Internet and widely circulated among advocates, shows the government has agreed to compensate her. Federal health officials have conceded that the five shots she received in July 2000 "significantly aggravated an underlying mitochondrial disorder," which manifested as a brain disease with features of autism. Autism family advocates say this shows the government is conceding — after years of blanket denials — that vaccines play a role in at least some autism cases.

Q: What do federal health officials say about the case?

A: The U.S. Department of Health and Human Services branch that administers the vaccine injury program says the government "continues to maintain the position that vaccines do not cause autism and has never concluded in any case that autism was caused by vaccination."

Q: What are mitochondrial disorders?

A: Mitochondria are tiny rod-like structures that serve as the energy-making machines inside cells. When mitochondria don't work properly, they produce less energy and can cause various body systems to fail.

Q: What causes the disorders?

A: For the most part, genes. Sometimes a person's mitochondria — if their genes make them susceptible — can be affected by environmental factors such as medications. The Georgia girl's family suspects her mitochondria were damaged by a mercury-based preservative in the vaccines she received. Tests didn't find a genetical link in her case, the family said.

Q: What's the relationship between mitochondrial disorders and autism?

A: While some children with mitochondrial disorders have autistic symptoms, the vast majority do not, said Dr. Bruce Cohen, a pediatric neurologist at the Cleveland Clinic and past-president of the Mitochondrial Medicine Society. Most autistic children do not have mitochondrial disease, he said.

Q: How can a mitochondrial disorder be aggravated by vaccinations?

A: Vaccination — like illnesses, starvation, extreme heat or any other stress on the body — may unmask a mitochondrial disorder, experts said. When a vaccine is injected, it causes the body to mount an immune response. This requires increased energy the body may not have if there is an underlying mitochondrial disorder. Still, Cohen said he recommends vaccination, even for most patients with diagnosed mitochondrial disorders. That's because of the greater danger posed by vaccine-preventable diseases.

Q: How common is this?

A: According to the United Mitochondrial Disease Foundation, at least one in every 4,000 children born in the U.S. each year will develop a mitochondrial disease by age 10. Many children are misdiagnosed with such things as atypical cerebral palsy, seizure disorders and other diseases. Adults also can be diagnosed with adult-onset mitochondrial disease.

Q: What does the case mean for the safety of vaccines?

A: Medical experts said parents should continue vaccinating their children because it protects them from diseases known to be deadly. If they're concerned, they should talk with their pediatrician.

Q: Where can I get more information?

A: United Mitochondrial Disease Foundation: www.umdf.org.

Sources: United Mitochondrial Disease Foundation; CDC; National Institutes of Health; Health Resources and Services Administration; and AJC research