In about 5 percent²² of autism cases, another disorder is also present.  Studying this kind of co-occurrence helps researchers who are trying to pinpoint the genes involved in autism.  Similar disorders or disorders with similar symptoms may have similar genetic origins.  In cases of one disorder commonly occurring with another, it could be that one is actually a risk factor for the other.  This kind of information can provide clues to what actually happens in autism. 

Some of these co-occurring disorders include:

• Epilepsy or seizure disorder—Nearly one-third²³ of those with autism also show signs of epilepsy by adulthood.  In most cases, medication can control and treat epilepsy effectively. 
• Tuberous sclerosis—About 6 percent²⁴ of those with autism also have tuberous sclerosis, a disorder that shares many symptoms with autism, including seizures that result from lesions, or cuts on the brain.
• Fragile X syndrome—Nearly 2.1 percent²⁵ of those with autism also have Fragile X, the most common inherited form of mental retardation.
• Mental retardation—About 25 percent²⁶ of persons with autism also have some degree of mental retardation.

Many people have treatable conditions in addition to their autism.  Sleep disorders, allergies, and digestive problems are commonly seen in those with ASDs, and many of these can be treated with environmental interventions and/or medication.  Treatment for these conditions may not cure autism, but it can improve the quality-of-life for people who have autism and their families.