Conditions comorbid to autism spectrum disorders
Encyclopedia
There are many conditions comorbid to autism spectrum disorders, such as fragile X syndrome
Fragile X syndrome
Fragile X syndrome , Martin–Bell syndrome, or Escalante's syndrome , is a genetic syndrome that is the most commonly known single-gene cause of autism and the most common inherited cause of intellectual disability...

 and epilepsy
Epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...

. In medicine
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....

 and in psychiatry
Psychiatry
Psychiatry is the medical specialty devoted to the study and treatment of mental disorders. These mental disorders include various affective, behavioural, cognitive and perceptual abnormalities...

, comorbidity
Comorbidity
In medicine, comorbidity is either the presence of one or more disorders in addition to a primary disease or disorder, or the effect of such additional disorders or diseases.- In medicine :...

 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 disorder
Genetic disorder
A genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....

s. However, autism
Autism
Autism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their...

 and other autism spectrum
Autism spectrum
The term "autism spectrum" is often used to describe disorders that are currently classified as pervasive developmental disorders. Pervasive developmental disorders include autism, Asperger syndrome, Childhood disintegrative disorder, Rett syndrome and Pervasive Developmental Disorder Not Otherwise...

 diagnoses, including Asperger syndrome
Asperger syndrome
Asperger's syndrome that is characterized by significant difficulties in social interaction, alongside restricted and repetitive patterns of behavior and interests. It differs from other autism spectrum disorders by its relative preservation of linguistic and cognitive development...

, are diagnosed strictly as a cognitive disability, as a brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

 disorder that begins in early childhood, persisting throughout adulthood, and affecting three crucial areas of development: communication, social interaction and creative
Creativity
Creativity refers to the phenomenon whereby a person creates something new that has some kind of value. What counts as "new" may be in reference to the individual creator, or to the society or domain within which the novelty occurs...

 or imaginative
Imagination
Imagination, also called the faculty of imagining, is the ability of forming mental images, sensations and concepts, in a moment when they are not perceived through sight, hearing or other senses...

 play.

Anxiety

Anxiety disorder
Anxiety disorder
Anxiety disorder is a blanket term covering several different forms of abnormal and pathological fear and anxiety. Conditions now considered anxiety disorders only came under the aegis of psychiatry at the end of the 19th century. Gelder, Mayou & Geddes explains that anxiety disorders are...

s are common among children with ASD, although there is no firm data. Symptoms are likely affected by age, level of cognitive functioning, degree of social impairment, and ASD-specific difficulties. Many anxiety disorders, such as social anxiety disorder
Social anxiety disorder
Social anxiety disorder , also known as social phobia, is an anxiety disorder characterized by intense fear in social situations causing considerable distress and impaired ability to function in at least some parts of daily life...

, are not commonly diagnosed in people with ASD because such symptoms are better explained by ASD itself, and it is often difficult to tell whether symptoms such as compulsive checking are part of ASD or a co-occurring anxiety problem. The prevalence of anxiety disorders in children with ASD has been reported to be anywhere between 11% and 84%; the wide range is likely due to differences in the ways the studies were conducted.

Bipolar disorder

Bipolar disorder
Bipolar disorder
Bipolar disorder or bipolar affective disorder, historically known as manic–depressive disorder, is a psychiatric diagnosis that describes a category of mood disorders defined by the presence of one or more episodes of abnormally elevated energy levels, cognition, and mood with or without one or...

, 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
Autistic enterocolitis
"Autistic enterocolitis" is a controversial term first used by discredited British gastroenterologist Andrew Wakefield to describe a number of common clinical symptoms and signs which he contends are distinctive to autism...

, by Dr. Andrew Wakefield
Andrew Wakefield
Andrew Wakefield is a British former surgeon and medical researcher, known as an advocate for the discredited claim that there is a link between the measles, mumps and rubella vaccine, autism and bowel disease, and for his fraudulent 1998 research paper in support of that claim.Four years after...

; this diagnostic terminology, however, has been questioned by medical experts. Constipation, often with overflow, or encopresis
Encopresis
Encopresis is involuntary fecal soiling in adults and children who have usually already been toilet trained. Persons with encopresis often leak stool into their undergarments.-Prevalence:The estimated prevalence of encopresis in four-year-olds is between one and three percent...

, is often associated with developmental disorders in children, and is often difficult to resolve, especially among those with behavioral and communication problems.

Depression and other psychopathological disorders

Phobia
Phobia
A phobia is a type of anxiety disorder, usually defined as a persistent fear of an object or situation in which the sufferer commits to great lengths in avoiding, typically disproportional to the actual danger posed, often being recognized as irrational...

s, depression
Clinical depression
Major depressive disorder is a mental disorder characterized by an all-encompassing low mood accompanied by low self-esteem, and by loss of interest or pleasure in normally enjoyable activities...

 and other psychopathological
Psychopathology
Psychopathology is the study of mental illness, mental distress, and abnormal/maladaptive behavior. The term is most commonly used within psychiatry where pathology refers to disease processes...

 disorders have often been described along with ASD but this has not been assessed systematically.

Fragile X syndrome

Fragile X syndrome
Fragile X syndrome
Fragile X syndrome , Martin–Bell syndrome, or Escalante's syndrome , is a genetic syndrome that is the most commonly known single-gene cause of autism and the most common inherited cause of intellectual disability...

 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 a person with autism 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.

ADHD

The Diagnostic and Statistical Manual of Mental Disorders
Diagnostic and Statistical Manual of Mental Disorders
The Diagnostic and Statistical Manual of Mental Disorders is published by the American Psychiatric Association and provides a common language and standard criteria for the classification of mental disorders...

 (4th edition) prohibits the co-diagnosis of an ASD and attention-deficit hyperactivity disorder
Attention-deficit hyperactivity disorder
Attention deficit hyperactivity disorder is a developmental disorder. It is primarily characterized by "the co-existence of attentional problems and hyperactivity, with each behavior occurring infrequently alone" and symptoms starting before seven years of age.ADHD is the most commonly studied and...

 (ADHD). However, clinically significant symptoms of these two conditions commonly co-occur, and children with both sets of symptoms may respond poorly to standard ADHD treatments, and may benefit from additional types of medications or from behavioral or other therapies.

Mental retardation

The fraction of autistic individuals who also meet criteria for mental retardation has been reported as anywhere from 25% to 70%, a wide variation illustrating the difficulty of assessing autistic intelligence. For example, 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 normal intelligence in about 94% of 53 children with PDD-NOS. Conversely, a 2008 study estimated that 28% of adolescents with intellectual disabilities have autism. A 2007 study reported that autistics score higher in Raven's Matrices than in Wechsler tests
Wechsler Adult Intelligence Scale
The Wechsler Adult Intelligence Scale intelligence quotient tests are the primary clinical instruments used to measure adult and adolescent intelligence. The original WAIS was published in February 1955 by David Wechsler, as a revision of the Wechsler-Bellevue Intelligence Scale...

; a 2008 study found a similar effect, but to a much lesser degree and only for individuals with Wechsler IQs less than 85. By definition, the diagnosis of Asperger's excludes mental retardation.

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
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

 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
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 (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
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...

 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
Asperger syndrome
Asperger's syndrome that is characterized by significant difficulties in social interaction, alongside restricted and repetitive patterns of behavior and interests. It differs from other autism spectrum disorders by its relative preservation of linguistic and cognitive development...

 and other diagnostic schemes include descriptions of motor clumsiness
Motor skills disorder
Motor skills disorder is a human developmental disorder that impairs motor coordination in daily activities. It is neurological in origin...

. 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
Proprioception
Proprioception , from Latin proprius, meaning "one's own" and perception, is the sense of the relative position of neighbouring parts of the body and strength of effort being employed in movement...

 (sensation of body position) on measures of apraxia
Apraxia
Apraxia is a disorder caused by damage to specific areas of the cerebrum. Apraxia is characterized by loss of the ability to execute or carry out learned purposeful movements, despite having the desire and the physical ability to perform the movements...

 (motor planning disorder), balance, tandem gait
Tandem gait
Tandem gait is a gait where the toes of the back foot touch the heel of the front foot at each step. Neurologists sometimes ask patients to walk in a straight line using tandem gait as a test to help diagnose ataxia, especially truncal ataxia, because sufferers of these disorders will have an...

, and finger-thumb apposition.

Obsessive-compulsive disorder

Obsessive-compulsive disorder
Obsessive-compulsive disorder
Obsessive–compulsive disorder is an anxiety disorder characterized by intrusive thoughts that produce uneasiness, apprehension, fear, or worry, by repetitive behaviors aimed at reducing the associated anxiety, or by a combination of such obsessions and compulsions...

 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
Autism
Autism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their...

, for instance an obsession to study an interest.

Tourette syndrome

The prevalence of Tourette syndrome
Tourette syndrome
Tourette syndrome is an inherited neuropsychiatric disorder with onset in childhood, characterized by multiple physical tics and at least one vocal tic; these tics characteristically wax and wane...

 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
Dopamine
Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...

, glutamate or serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...

 abnormalities.

Seizures

ASD is also associated with epilepsy
Epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...

, with variations in risk of epilepsy due to age, cognitive level, and type of language disorder. One in four autistic children develops seizure
Seizure
An epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...

s, 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
Stimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....

 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
Twenty Questions
Twenty Questions is a spoken parlor game which encourages deductive reasoning and creativity. It originated in the United States and escalated in popularity during the late 1940s when it became the format for a successful weekly radio quiz program....

; these problems were somewhat more marked among adults.
Several studies have reported associated motor problems that include poor muscle tone, poor motor planning
Apraxia
Apraxia is a disorder caused by damage to specific areas of the cerebrum. Apraxia is characterized by loss of the ability to execute or carry out learned purposeful movements, despite having the desire and the physical ability to perform the movements...

, and toe walking
Toe walking
Toe walking refers to a condition where a person walks on his or her toes without putting much weight on the heel or any other part of the foot. Toe-walking in toddlers is common. These children usually adopt a normal walking pattern as they grow older...

; ASD is not associated with severe motor disturbances.

Tuberous sclerosis

Tuberous sclerosis
Tuberous sclerosis
Tuberous sclerosis or tuberous sclerosis complex is a rare multi-system genetic disease that causes non-malignant tumors to grow in the brain and on other vital organs such as the kidneys, heart, eyes, lungs, and skin. A combination of symptoms may include seizures, developmental delay, behavioral...

 is a rare genetic disorder that causes benign tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...

s 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
Pervasive developmental disorder
Pervasive developmental disorders is a diagnostic category refers to a group of disorders characterized by delays or impairments in communication, social behaviors, and cognitive development.Pervasive developmental disorders include Autism, Asperger's syndrome, Rett's syndrome, Childhood...

.
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