That is difficult to tell. One study in Portugal showed that five out of sixty-nine (or 7.2 percent) of the autistic children who were studied suffered from a mitochondrial disorder similar to Hannah’s. It is unclear if that percentage will be accurate across different countries and different populations of autistic children. It does suggest, however, that the majority of autistic children are not affected by this type of mitochondrial disorder. However, there may be other metabolic disorders that have not yet been discovered that contribute to autism.
It is also important to note that Hannah was able to receive extensive and very expensive testing, including a mitochondrial DNA analysis that showed the exact mutation that caused her problems. Most families are not able to arrange for such testing. For those who are interested, Hannah’s father, Dr. Jon Poling, is a neurologist and published a scientific paper on Hannah and other children with autism.