Disorders that co-occur with autism spectrum disorder

autystyczny chłopiec
autystyczny chłopiec

Published: 29-12-2023

Autism spectrum disorder is diagnosed based on deficits in communication and interaction with other people and the presence of restricted and repetitive behaviors, interests or activities. But that’s not all. People with autism often struggle with co-occurring problems, including mental disorders, sleep disorders, digestive system disorders, ADHD, and epilepsy.

I don’t want to devote too much space here to describing the symptoms of autism spectrum disorder, so I will only mention that, as the name suggests, it is a spectrum, which means that people with this diagnosis differ greatly in the severity of various symptoms. In DSM-5, the latest classification of mental disorders of the American Psychiatric Association, Asperger’s Syndrome is included in autism spectrum disorders. Such a diagnosis can be obtained both by a person who cannot speak, cannot communicate with the environment and needs lifelong care, and by someone who has completed studies, works, has a husband/wife and children and in whom a non-specialist will not notice any symptoms of autism.

In the rest of the article, I will use the terms “autism spectrum”, “autism”, “ASD” (autism spectrum disorder) and “autistic person” interchangeably.

For better readability, I do not include links to sources in the text, but you will find everything at the end in the bibliography.

Sensory integration disorders in ASD

Sensory integration is a neurobiological process that involves the processing of sensory stimuli by the brain. Its disorders lead to excessive or too weak sensitivity to certain sensory stimuli. Most people on the autism spectrum have sensory integration disorders, and this may affect one or more of the senses. For example, a person with a hypersensitive sense of hearing may not tolerate noise well because the sound intensity, which may be average for other people, will be too loud for him/her. Disturbances in the processing of the sense of touch may manifest themselves as excessive resistance or excessive sensitivity to pain, reluctance to eat certain foods due to their consistency, or reluctance to put on certain clothes. People with an overly reactive vestibular sense (responsible for the sense of balance) often appear clumsy and avoid many playground activities as children (e.g., they are afraid of swings and slides). A vestibular sense that is too weakly reactive prompts us to look for activities that will stimulate this sense. This could be, for example, spinning in circles, jumping, etc.

Sensory integration disorders are so common among autistic people that they are included among the diagnostic criteria in the DSM-5 (but do not necessarily have to be present to be diagnosed with ASD).

Mental disorders in the autism spectrum


Data on the occurrence of depression in people on the autism spectrum vary depending on the source, but all agree that it is a common disorder among such people. It is estimated that in the general population depression occurs in several percent of people, while in the population of people with ASD – in approximately 25%.

There are several reasons why it is difficult to estimate the exact rate of depression. Firstly, many people on the autism spectrum suffer from alexithymia, which is difficulty in naming their own emotional states and recognizing them. Such people may not be able to describe their emotions, and sometimes they do not even notice them. Depression may manifest itself in psychosomatic problems, such as abdominal pain, migraines, shortness of breath, dizziness, cardiac arrhythmia – this is the so-called masked depression. Other unusual symptoms of depression are also common in autistic people, such as aggression, frequent irritability, mood swings, and changes in sensitivity to various stimuli. This makes diagnosis difficult and may leave many people undiagnosed. Second, some symptoms of autism spectrum disorder are similar to symptoms of depression, such as difficulty concentrating, social withdrawal, lack of eye contact, or flat affect (lack of emotional expression). On the one hand, this may result in underdiagnosis of depression if the symptoms of depression are considered a symptom of autism, but on the other hand, it may also result in overdiagnosis if the autistic trait is considered a symptom of depression.

The occurrence of depression is largely influenced by the fact that autistic people, due to their differences, have difficulties in establishing and maintaining satisfactory contacts with other people. They often experience rejection, loneliness, misunderstanding, and bullying at school. However, it is possible that genetic predisposition to depression also plays a role.

Anxiety disorders

About half, or perhaps even more, of autistic people experience anxiety disorders such as generalized anxiety disorder, separation anxiety, social anxiety, phobias, and obsessive-compulsive disorder. The causes are similar to those of depression, i.e. the occurrence of anxiety disorders may be influenced by, for example, peer violence, but also generally by stress related to social contacts. They are difficult for autistic people because what is intuitive for neurotypical people, from them often requires conscious mental effort. Anxiety states can also be triggered by various types of unpredictable situations or by stimuli to which a person is excessively sensitive.

Sleep disorders in the autism spectrum

It is estimated that up to 80% of autistic people may have sleep problems. These include difficulty falling asleep, waking up during the night, waking up too early and poor sleep quality. There may be many reasons, including: problems with the digestive system, increased stimulation of the nervous system, sensitivity to stimuli, hormonal imbalance (e.g. abnormalities in melatonin secretion), restless legs syndrome. People with ASD also more often have disturbances in the circadian sleep-wake rhythm and spend less time during sleep in the REM phase. In an average person, 25% of sleep time is in the REM phase, while in people on the autism spectrum it is about 15%, which means that such people need to sleep longer to get the appropriate amount of time in the REM phase.

Lack of sleep leads to the intensification of many symptoms and problems associated with autism. Increases, among others: aggression, problems with attention and learning, increases hypersensitivity to stimuli, anxiety and depressive disorders.

ADHD and autism spectrum

ADHD occurs in approximately 50-70% of autistic people, and such frequent co-occurrence has recently led some researchers (Hours, Recasens and Baleyte) to put forward the thesis that attention disorders should be included in the diagnostic criteria of autism and not always treated as co-occurring ADHD. Especially since of the two types of ADHD – the type with predominance of hyperactivity and the type with predominance of concentration disorders, it is the latter that most often occurs in people on the autism spectrum.

People with AuDHD – as co-occurring ADHD and autism are commonly referred to – often experience certain contradictions. For example, they may make spontaneous plans (a trait of ADHD), but at the same time become angry if something interrupts these plans (a trait of ASD). They like to engage deeply in their interests (an ASD trait), but at the same time need to bounce between different interests to stay engaged (an ADHD trait). Being on the autism spectrum may make them angry if someone is late for a meeting, but because of ADHD they have trouble being punctual themselves.

Neurological disorders in the autism spectrum

Autistic people have a higher incidence of certain neurological disorders than the general population, including epilepsy, macrocephaly, hydrocephalus, cerebral palsy, migraines/headaches, and congenital defects of the nervous system.

Dysfunction of the autonomic nervous system is also common in people with ASD. There is often an increase in the activity of the sympathetic nervous system and a decrease in the activity of the parasympathetic part. This autonomic imbalance may manifest itself as changes in heart rate, an atypical pupillary light reflex, an atypical autonomic response to anxiety, or elevated plasma norepinephrine levels.


Epilepsy occurs in approximately 10-30% of people on the autism spectrum. Like autism, epilepsy is a spectrum, meaning it can manifest itself in different ways and with varying degrees of severity. An epileptic seizure does not always involve convulsions, muscle tension and loss of consciousness. It can also manifest itself more subtly, such as staring into space and blinking rapidly. It can sometimes be difficult to distinguish from autism-related behaviors.

The co-occurrence of epilepsy and autism results from the presence of common neurological mechanisms. Synucleinopathy (abnormal accumulation of alpha-synuclein protein aggregates in neurons, nerve fibers, or glial cells), synaptopathies (synaptic dysfunction in the brain, spinal cord, or peripheral nervous system), inflammation, and abnormal glial cell interactions are some of the mechanisms that cause both autistic symptoms as well as epilepsy.

Autism spectrum and intelligence quotient

Several decades ago, scientific publications indicated that the vast majority of autistic people have a reduced IQ, but this changes over time. A collective analysis of research from 1966 to 2001 indicated that approximately 70% of people with autism have an IQ lower than 70, a publication from 2007 showed that it is 50%, and according to data from 2014 – 31%. This is probably due to the change in the diagnostic criteria for autism spectrum disorder and greater awareness of this disorder, which means that it is more and more often diagnosed in people who are intellectually normal. Interestingly, people on the autism spectrum are also more likely to have above-average intelligence, i.e. both abnormally high and abnormally low IQ often co-occur with autism.

Prosopagnosia in the autism spectrum

Prosopagnosia is difficulty recognizing faces, which you can read about in my article “Face blindness, or prosopagnosia”. It occurs in approximately 2% of people in the general population, while among autistic people this percentage is approximately 36%.

Gastrointestinal problems in autism spectrum disorder

Gastrointestinal problems occur several times more often in autistic people than in the general population. These include, among others: chronic constipation, chronic diarrhea, gastroesophageal reflux, nausea and/or vomiting, chronic flatulence, abdominal discomfort, ulcers, colitis. Food intolerances and allergies are also common.

It is not entirely clear why these types of problems are so common in people with ASD. This may be due to genetic factors and abnormal intestinal microflora, but stress factors may also play a role. People on the autism spectrum are more likely to experience stress and anxiety disorders, which may affect digestive system disorders. The fact that many autistic people are very picky eaters and have a very monotonous diet may also contribute to gastrointestinal problems.

However, it is clear that gastrointestinal problems contribute to the severity of behavioral problems. Children with ASD with frequent abdominal pain, flatulence, diarrhea, constipation, or pain during defecation have higher scores on irritability, social withdrawal, stereotypy, and hyperactivity compared to children who do not have frequent GI symptoms.

Metabolic disorders in the autism spectrum

Metabolic disorders are inborn errors of metabolism that may affect the synthesis or function of proteins (e.g. enzymes), fats or carbohydrates, causing the accumulation or deficiency of certain metabolites and, consequently, the appearance of various disease symptoms. Several types of metabolic disorders have been observed to occur more frequently in people with autism: mitochondrial disorders, creatine metabolism disorders, disorders of some amino acids, disorders of folic acid or vitamin B12 metabolism, and lysosomal storage diseases.

Immune system disorders in the autism spectrum

Approximately 25% of children with ASD have immune system dysfunction. This may involve deficits in immunoglobulin G (IgG) and supplementing them intravenously may improve social and cognitive skills in autistic children. Some studies have also shown that antineuronal antibodies may play a role in the development of autistic symptoms. In addition, people on the autism spectrum are more likely to have various types of allergies – the previously mentioned food allergies, but also asthma and atopic diseases.

Genetic disorders in the autism spectrum

There are several genetic disorders associated with the high incidence of autism.

Fragile X syndrome

Fragile X syndrome is the most common cause of intellectual disability. Approximately 2-3% of children with ASD have this genetic disorder and of those with this disorder, approximately 25-33% have autism. Children who are on the autism spectrum and have fragile X syndrome have higher rates of social anxiety, intellectual disability, hyperarousal and repetitive behaviors than those who have autism spectrum disorder of unknown cause.

Down syndrome

Another genetic disorder in which autism is common is Down Syndrome. It is estimated that up to 40% of people with Down Syndrome also have autism spectrum disorder. Here too, the co-occurrence of these disorders increases various symptoms. Such people are more likely to experience, for example, self-aggressive behaviors (e.g. banging their heads, biting themselves), repetitive motor behaviors (e.g. clapping), problems with attention, sleep problems, neurological disorders (e.g. epilepsy, severe decreased muscle tone) and other.

Tuberous sclerosis

Tuberous sclerosis is a disease characterized by skin lesions and non-cancerous tumors. They may appear in various organs, including the liver, kidneys, heart and brain, which leads to neurological complications. Approx. 25-50% of people with tuberous sclerosis also have autism spectrum disorder.

Dravet syndrome

Dravet syndrome manifests itself with severe epilepsy that does not respond well to treatment. The first epileptic seizures appear already in infancy, and later there are various problems in the child’s development, such as motor delays, speech delays, sensory integration disorders, and sleep problems. Approximately 25-60% of children are diagnosed with autism spectrum disorder.

Pitt-Hopkins syndrome

Pitt-Hopkins syndrome is a rare genetic syndrome that causes developmental delays, moderate to severe intellectual disability, behavioral differences, distinctive facial features and breathing problems such as episodes of rapid breathing (hyperventilation) and breath-holding. They also often include, among others: sleep disorders, epileptic seizures, constipation and myopia. Due to the similarity of symptoms, many specialists treat it as an autism spectrum disorder.

Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome is a developmental disorder that includes, among others: distinctive facial features, small head size (microcephaly), intellectual disability or learning difficulties, and behavioral problems. About half of people with this disorder are diagnosed with autism. Developmental defects of the heart, lungs, kidneys, gastrointestinal tract and genitals are also common. Babies with Smith-Lemli-Opitz syndrome have poor muscle tone (hypotonia), difficulty feeding, and usually grow slower than other babies. Most affected people have their second and third toes fused together (syndactyly), and some have extra fingers and toes (polydactyly).

The symptoms of Smith-Lemli-Opitz syndrome vary greatly. People with mild disease may have only minor physical abnormalities and learning and behavioral problems. Severe cases can be life-threatening and include profound intellectual disability and serious physical abnormalities.

The incidence of Smith-Lemli-Opitz syndrome worldwide is estimated at approximately 1:20,000-1:60,000, but interestingly, it occurs exceptionally often in my geographical region. In Poland, this disorder occurs in 1:2,300-1:4,000 people.

Ehlers-Danlos syndrome

These are connective tissue disorders that are divided into 13 types. The most common type is the hypermobile type, which is mainly manifested by excessive joint mobility and excessively elastic skin. This disorder is more common in people with neurodevelopmental disorders (not only autism, but also ADHD and Tourette’s syndrome) than in neurotypical people.

Other genetic disorders

Some publications mention the frequent occurrence of autism spectrum disorder also in people with muscular dystrophies (e.g. Duchenne dystrophy), in people with Sotos syndrome (so-called cerebral gigantism), with Angelman syndrome (called the “happy puppet syndrome” due to its characteristic appearance and behavior) and in people with Ito hypomelanosis (a neurocutaneous disorder).

Orthopedic problems in the autism spectrum

Autistic people often move differently than neurotypical people – they walk with a different cadence, their hips and ankles move differently, and children often walk on their toes. This can lead to greater stress on the lower back and legs, and walking on the toes can result in problems with ankle flexion.

It has also been noticed that people on the autism spectrum are more likely to suffer from scoliosis (curvature of the spine) and reduced bone thickness.

LGBTQ and the autism spectrum

These are not disorders, but they occur so often in autistic people that I decided to mention it. Exact numbers are unknown, but it is estimated that people on the autism spectrum are 2-3 times more likely to be gay, lesbian or bisexual than neurotypical people. They are also more likely to be transgender, i.e. they identify as a person of the opposite gender than that assigned at birth, or non-binary (they identify differently than as a woman or a man).

Can autism be cured?

Autism itself cannot be cured, but there are treatments for some disorders that co-occur with ASD. Importantly, eliminating comorbid problems often also has a beneficial effect on autism symptoms. For example, a person with an allergy or intolerance to gluten, casein or another food ingredient, after eliminating it from the diet, will not only improve the functioning of his digestive system, but may also become less irritable and be more willing to interact with people. Better sleep means, among other things, greater tolerance to sensory stimuli and better concentration. The quality of life can also be significantly improved by treatment for depression and anxiety disorders. Therefore, it is important to diagnose other disorders and implement appropriate treatment wherever possible.


Author: Maja Kochanowska

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