About one percent of the population has epilepsy, which is defined as more than one unprovoked seizure.
Seizures are caused by excess electrical activity in the brain. Scientists can detect this activity using electroencephalograms (EEG). In this technique, electrodes on the scalp measure wave patterns among large groups of neurons. During a seizure, the EEG reveals an abnormal pattern of spikes and waves.
Severe tonic-clonic seizures, which cause physical convulsions and blackouts, are impossible to miss, but milder seizures may produce a few symptoms. Some of these milder symptoms, including blank stares, tics and inattention, are also associated with autism, which can make it difficult to diagnose epilepsy in individuals with autism.
Relevance to autism:
Approximately one-third of individuals with autism suffer from seizures. The proportion is higher in those with certain forms of syndromic autism, for example fragile X syndrome and Rett syndrome. Consequently, the number of individuals with epilepsy who also have autism ranges widely, from 5 to 46 percent1.
Though males are four times more likely than females to have autism, among individuals with both autism and epilepsy, the gender ratio drops from two to one.
Individuals who have both autism and epilepsy are also more likely to have intellectual disability2. Researchers believe that the cognitive impairment could be the result of seizures disturbing brain development.
Autism is often diagnosed later in individuals with epilepsy. Alternately, some individuals diagnosed with autism in childhood do not develop seizures until adolescence or later.
Certain mechanisms are believed to underlie both disorders, including an imbalance between excitatory neurons that activate signals in the brain and inhibitory neurons that dampen neuronal activity.
Genetic studies have turned up many candidate genes and chromosomal regions likely to be responsible for one or both disorders. For example, a deletion on chromosome 15q13.3 has been linked to autism, schizophrenia and mental retardation. A 2009 study revealed that 15q13.3 deletion is also the most common risk factor for epilepsy.
Sudden unexplained death in epilepsy:
Sudden unexplained death in epilepsy — SUDEP for short — is believed to be responsible for the deaths of more than 4,000 people in the U.S. each year. Most of them are younger than age 223.
Though the causes of SUDEP remain murky, researchers have identified certain risk factors, which include greater frequency of tonic-clonic seizures and use of more than one therapeutic drug.
Individuals with autism who have no known history of seizures also appear to be at risk of sudden unexpected death. Some proportion of these individuals are likely to have undiagnosed epilepsy as EEGs show unusual brain wave patterns in more than half of individuals with autism.
A 2011 study reported that half of all deaths among people with autism, epilepsy or both disorders in California over a period of three years were attributed to unknown causes4.
A mysterious cluster of sudden deaths among young people with a duplication in the 15q11-13 chromosomal region associated with autism and epilepsy has drawn more attention to the phenomenon. Between April 2006 and January 2009, 11 young people between the ages of 7 and 26 years with 15q duplication syndrome died suddenly.
A number of the young people were taking sedative medications to control their seizures at the time of their deaths. The scientific advisory board of the family support group called the Dupe15q Alliance put out an advisory warning that individuals with the syndrome might be at higher risk of sudden death. The advisory noted the possibility of respiratory complications related to certain sedative drugs, including Ambien, Librium, Valium, Ativan and phenobarbital, which are frequently prescribed to relieve anxiety and control seizures.