Conditions comorbid to autism spectrum disorders

Overview
There are many conditions comorbid to autism spectrum disorders, ranging from concurrent psychiatric conditions and neuroinflammation to a variety of colon and digestive disorders. In medicine and in psychiatry, comorbidity describes the effect of other diseases an individual patient might have other than the primary disease of interest. About 10–15% of autism cases have an identifiable Mendelian (single-gene) condition, chromosome abnormality, or other genetic syndrome, and ASD is associated with several genetic disorders. However, autism and other autism spectrum diagnoses, including Asperger syndrome, are diagnosed strictly as a cognitive disability, as a brain disorder that begins in early childhood, persisting throughout adulthood, and affecting three crucial areas of development: communication, social interaction and creative or imaginative play.

Bipolar disorder
Bipolar disorder, or manic-depression, is itself comorbid with a number of conditions, including autism. Autism includes some symptoms commonly found in mood and anxiety disorders.

Bowel disease
Some children with autism also have gastrointestinal (GI) symptoms, but there is a lack of published rigorous data to support the theory that autistic children have more or different GI symptoms than usual. It has been claimed that up to fifty percent of children with autism experience persistent gastrointestinal tract problems, ranging from mild to moderate degrees of inflammation in both the upper and lower intestinal tract. This has been described as a syndrome, autistic enterocolitis, by Dr. Andrew Wakefield; this diagnostic terminology, however, has been questioned by medical experts. Constipation, often with overflow, or encopresis, is often associated with developmental disorders in children, and is often difficult to resolve, especially among those with behavioral and communication problems.

Depression and anxiety disorders
Phobias, depression and other psychopathological disorders have often been described along with ASD but this has not been assessed systematically.

Fragile X syndrome
Fragile X syndrome is the most common inherited form of mental retardation. It was so named because one part of the X chromosome has a defective piece that appears pinched and fragile when under a microscope. Fragile X syndrome affects about two to five percent of people with ASD. It is important to have an autistic checked for Fragile X, especially if the parents are considering having another child. If one child has Fragile X, there is a one-in-two chance that boys born to the same parents will have Fragile X (see Mendelian genetics). Other members of the family who may be contemplating having a child may also wish to be checked for the syndrome.

Hyperactivity and attention abnormalities
Attention-deficit hyperactivity disorder (ADHD) is one of the most commonly diagnosed and controversial neuropsychiatric disorders among children, and is increasingly recognized as afflicting adults as well. Its symptoms include inattention, hyperactivity, and impulsivity. According to sources such as the CDC, the causes are currently unknown, and it is thought that the term covers a variety of related disorders. There is no single medical test that can accurately diagnose ADHD, though there are assessment tools.

Mental retardation
Autism is associated with mental retardation: a 2001 British study of 26 autistic children found about 30% with intelligence in the normal range (IQ above 70), 50% with mild to moderate retardation, and about 20% with severe to profound retardation (IQ below 35). For ASD other than autism the association is much weaker: the same study reported about 94% of 65 children with PDD-NOS or Asperger's had normal intelligence. When tested, some areas of ability may be normal or superior, while others may be especially weak. For example, an autistic individual may do well on the parts of the test that measure visual skills but earn low scores on the language subtests.

A 2006 review questioned the common assumption that most children with autism are mentally retarded. It is possible that the association between mental retardation and autism is not because they usually have common causes, but because the presence of both makes it more likely that both will be diagnosed.

Neuroinflammation and immune disorders
The role of the immune system and neuroinflammation in the development of autism is controversial. Until recently, there was scant evidence supporting immune hypotheses, but research into the role of immune response and neuroinflammation may have important clinical and therapeutic implications. The exact role of heightened immune response in the central nervous system (CNS) of patients with autism is uncertain, but may be a primary factor in triggering and sustaining many of the comorbid conditions associated with autism. Recent studies indicate the presence of heightened neuroimmune activity in both the brain tissue and the cerebrospinal fluid of patients with autism, supporting the view that heightened immune response may be an essential factor in the onset of autistic symptoms.

Motor clumsiness
The initial accounts of Asperger syndrome and other diagnostic schemes include descriptions of motor clumsiness. Children with ASD may be delayed in acquiring motor skills that require motor dexterity, such as bicycle riding or opening a jar, and may appear awkward or "uncomfortable in their own skin". They may be poorly coordinated, or have an odd or bouncy gait or posture, poor handwriting, or problems with visual-motor integration, visual-perceptual skills, and conceptual learning. They may show problems with proprioception (sensation of body position) on measures of apraxia (motor planning disorder), balance, tandem gait, and finger-thumb apposition.

Obsessive-compulsive disorder
Obsessive-compulsive disorder is characterized by recurrent obsessional thoughts or compulsive acts.

Obsessional thoughts are ideas, images or impulses that enter the individual's mind again and again in a stereotyped form. They are almost invariably distressing (because they are violent or obscene, or simply because they are perceived as senseless) and the sufferer often tries, unsuccessfully, to resist them. They are, however, recognized as the individual's own thoughts, even though they are involuntary and often repugnant.

Compulsive acts or rituals are stereotyped behaviours that are repeated again and again. They are not inherently enjoyable, nor do they result in the completion of inherently useful tasks.

It must be recognized that this is different from the obsessions that are a feature of autism spectrum disorders in that the obsessions are not enjoyable or in any way beneficial, which can sometimes be the case with autism, for instance an obsession to study an interest.

Tourette syndrome
The prevalence of Tourette syndrome among individuals with autism is estimated to be 6.5%, higher than the 2% to 3% prevalence for the general population. Several hypotheses for this association have been advanced, including common genetic factors and dopamine or serotonin abnormalities.

Seizures
ASD is also associated with epilepsy, with variations in risk of epilepsy due to age, cognitive level, and type of language disorder. One in four autistic children develops seizures, often starting either in early childhood or adolescence. Seizures, caused by abnormal electrical activity in the brain, can produce a temporary loss of consciousness (a "blackout"), a body convulsion, unusual movements, or staring spells. Sometimes a contributing factor is a lack of sleep or a high fever. An EEG can help confirm the seizure's presence.

Sensory problems
Unusual responses to sensory stimuli are more common and prominent in autistic children, although there is no good evidence that sensory symptoms differentiate autism from other developmental disorders. The responses may be more common in children: a pair of studies found that autistic children had impaired tactile perception while autistic adults did not. The same two studies also found that autistic individuals had more problems with complex memory and reasoning tasks such as Twenty Questions; these problems were somewhat more marked among adults. Several studies have reported associated motor problems that include poor muscle tone, poor motor planning, and toe walking; ASD is not associated with severe motor disturbances.

Tuberous sclerosis
Tuberous sclerosis is a rare genetic disorder that causes benign tumors to grow in the brain as well as in other vital organs. It has a consistently strong association with the autism spectrum. One to four percent of autistic people also have tuberous sclerosis. Studies have reported that between 25% and 61% of individuals with tuberous sclerosis meet the diagnostic criteria for autism with an even higher proportion showing features of a broader pervasive developmental disorder.