Comorbidity and autism spectrum disorder

Nearly three-quarters of children with autism spectrum disorder (ASD) also have another medical or psychiatric condition. This is called ‘comorbidity’, and the conditions are often called ‘comorbid’ conditions.

Comorbid conditions can appear at any time during a child’s development. Some might not appear until later in adolescence or adulthood. Sometimes these comorbid conditions have symptoms that affect how well ASD therapies and interventions work. So it’s important to identify the conditions and treat them separately.

Here are some of the common comorbid conditions that might be diagnosed in children with ASD.


People with anxiety have a range of symptoms including tension, restlessness, hyperactivity, worry and fear. For children with autism spectrum disorder (ASD), anxiety might show up as stimming more often, asking questions over and over again, hurting themselves, or having trouble getting to sleep.

How common is anxiety in children with autism spectrum disorder?
Anxiety is common among children with ASD. About 40-60% of children with ASD also have anxiety.

Social anxiety is one of the most common anxiety disorders. Social anxiety probably happens because people with ASD often have social difficulties that can make them feel stressed and anxious.

How is anxiety treated?
Medication, behaviour therapy, cognitive behaviour therapy and relaxation techniques can all be used to treat anxiety.

Find out more
Anxiety in children with autism spectrum disorder

Attention deficit hyperactivity disorder (ADHD)

Many children have trouble with thinking before they act, sitting still and focusing. But in children with attention deficit hyperactivity disorder (ADHD), these behaviours can be extreme and have a big impact on their daily life. The behaviours usually happen together, although some children can be mainly inattentive.

How common is ADHD in children with autism spectrum disorder?
Autism spectrum disorder (ASD) and ADHD share some common characteristics like not seeming to listen when people speak, interrupting, or intruding on other people’s personal space. Many children with ASD have behaviour that’s very similar to ADHD.

How is ADHD treated?
There’s no cure, but children and teenagers can manage ADHD using behaviour strategies, medication, or a combination of the two.

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Bipolar disorder

Bipolar disorder is a psychiatric condition. People with bipolar disorder have both extreme emotional highs (mania) and extreme lows (depression).

The depression can be quite obvious – the person will probably have low mood, lack of motivation, trouble sleeping and poor appetite. Mania can be harder to spot. Its symptoms include extreme self-esteem, less need for sleep, more talking and higher activity levels than usual.

Children who have bipolar disorder have big and quick changes in mood and behaviour. When they’re going through these mood changes, they might also have trouble paying attention, sitting still and behaving appropriately.

How common is bipolar disorder in children with autism spectrum disorder? 
There isn’t a lot of research into bipolar disorder and autism spectrum disorder (ASD), but studies suggest that it’s not very common in young children with ASD.

How is bipolar disorder treated?
Treatment is usually long term. It often involves medication. There are some behaviour treatments that work.

Find out more
National Institute of Mental Health – Bipolar disorder

Clinical depression

Symptoms of depression include low mood, poor sleep and appetite, irritability and a loss of motivation. In children depression symptoms can also be cranky moods rather than just sadness and low moods.

How common is depression in children with autism spectrum disorder? 
Depression can be common in children with autism spectrum disorder (ASD), especially among higher-functioning children who know they have social difficulties.

People with ASD might be more likely to have symptoms of depression if they also have more severe characteristics of ASD, are older and have higher verbal IQ.

How is depression treated? 
Health professionals often use a combination of medication and psychotherapy, like cognitive behaviour therapy (CBT), to treat depression.

How well treatment works depends on several things, including the person’s optimism, control over things that cause stress and experience with other treatments. It also depends on how long the person has had depression and how much support the person gets from family and friends.

Also, CBT is a talking therapy. This means it can’t be used successfully with children and teenagers who don’t or can’t use language to communicate.

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Down syndrome

Down syndrome is a genetic disorder.

Most people have 23 pairs of chromosomes. People with Down syndrome (also called Trisomy 21) have an extra 21st chromosome. This causes characteristic facial features, developmental delays, intellectual disability, poor muscle tone, potential hearing and vision problems and congenital heart defects.

Down syndrome can be identified with tests during pregnancy. If it isn’t picked up then, it’s usually diagnosed at birth or in early infancy.

How common is Down syndrome in children with autism spectrum disorder?
Only a small number of children with autism spectrum disorder (ASD) also have Down syndrome. This is because Down syndrome is uncommon, occurring in only 1 in 1100 births. On the other hand, ASD is relatively common in children who have Down syndrome. Up to 40% of children with Down syndrome also have ASD.

How is Down syndrome treated?
The health problems associated with Down syndrome can be treated, usually very well.

Find out more
Down Syndrome Australia

Fragile X syndrome

Fragile X is a genetic disorder. It’s the most common cause of inherited intellectual disability.

Most boys with this condition have an intellectual disability, sometimes severe. In the early years this would be noticed as developmental delay. In girls the condition generally looks like a learning disability rather than intellectual impairment. Children with the condition have trouble communicating.

How common is Fragile X in children with autism spectrum disorder? 
Only a small number of children with autism spectrum disorder (ASD) also have Fragile X. Fragile X happens much less frequently than ASD. On the other hand, ASD is relatively common in children with Fragile X (25-33%).

How is Fragile X treated?
Treatment usually involves medication, early intervention and educational support.

Find out more
Fragile X Association of Australia

Gastrointestinal symptoms

The most common gastrointestinal symptoms for people with autism spectrum disorder (ASD) are chronic constipation, abdominal pain, diarrhoea and faecal incontinence. Other problems can include gastro-oesophageal reflux disease (GORD) and stomach bloating.

Gastrointestinal symptoms have been linked with more severe ASD and behaviour problems. It’s not clear why children with ASD have relatively high rates of gastrointestinal symptoms, but  it might be because of altered gut bacteria, increased gut permeability, longer food transit time through the gut, or low fibre intake.

How common are gastrointestinal symptoms in children with autism spectrum disorder?
Children with ASD and other developmental delays appear to have more gastrointestinal symptoms than other children.

How are gastrointestinal symptoms treated?
Because there are many reasons why a child might have gastrointestinal symptoms, the child will need a thorough medical examination before starting any treatment.

There’s no evidence to support the general use of a gluten-free or casein-free diet. But like some typically developing children, children with ASD might have gluten intolerance, or other food sensitivities, allergies or intolerances. If this is the case, specific diets can help.

Find out more
Autism Help – Gastrointestinal tract problems

Intellectual disability and developmental delays

Intellectual disability can be diagnosed when a child who is six years or older has an IQ below 70 as well as difficulties with daily tasks. In children under six years, the term developmental delay is used when children have significant cognitive and language delays.

Intellectual disability varies from person to person. Children with autism spectrum disorder (ASD) and intellectual disability might have uneven skills, so there might be some things that they’re quite good at and others they find hard.

In most cases, children with ASD have more trouble with verbal skills – like talking, listening and understanding – than with non-verbal skills like doing puzzles or drawing.

How common is intellectual disability in children with autism spectrum disorder?
In the past, it was thought that 50-60% of children with ASD had intellectual disability or developmental delays. But it’s now thought to be 30-40%, with another 20-25% having borderline intellectual disability with an IQ of 71-85.

This drop might be because IQ testing for children with ASD has improved, early intervention and education is better at addressing the learning needs of children with ASD, and more children without intellectual disability are being diagnosed with ASD.

Some researchers have argued that some children’s developmental delays might be caused by their social learning difficulties, rather than being a separate condition.

How is intellectual disability treated?
There might be significant improvements over time in some very young children with ASD who have developmental delay. But most children who have developmental delay might still have a lower than typical IQ when they’re older.

There’s no cure for intellectual disability, but it can be managed so that many people can live a reasonably normal life. Early intervention and education can support people with intellectual disability and their families.

Find out more
University of Hertfordshire – Understanding intellectual disability and health: autism

Motor difficulties

Children with motor difficulties might have difficulties with gross motor skills, like balance problems, clumsiness or walking problems. Or their difficulties might be related to fine motor skills, like problems with grasping objects, writing or using cutlery. Motor difficulties can also affect children’s mouths, making them hard to understand.

Muscle weakness often causes these difficulties. Abnormalities in the areas of the brain that control motor learning and function might cause the muscle weakness.

How common are motor difficulties in children with autism spectrum disorder?
About 80% of children with autism spectrum disorder (ASD) have some form of motor difficulty. Motor difficulties can happen in babies, children and adults, often before ASD symptoms become obvious. Some researchers think these difficulties might be early signs of ASD.

How are motor difficulties treated?
Early intervention that includes occupational and physical therapy is used to help children with motor difficulties.

Find out more 
Skills for action – Autism spectrum disorder and motor skills

Obsessive compulsive disorder (OCD)


People with OCD have thoughts that they don’t want but can’t get out of their heads. They behave in repetitive and compulsive ways to deal with these thoughts. For example, they might wash their hands over and over again, or arrange or count objects in patterns, as a way of cancelling out bad thoughts with good thoughts.

How common is OCD in children with autism spectrum disorder?
It’s hard to know how common OCD is among children with autism spectrum disorder (ASD) because these children also tend to have repetitive thoughts and behaviour. Because restricted and repetitive behaviour is more common in younger children with ASD, OCD seems to be more common at younger ages.

How is OCD treated?
OCD can be treated with behaviour therapy, cognitive therapy, medications or any combination of the three.

Find out more
Australian Psychological Society – Obsessive-compulsive disorder

Seizures and epilepsy


The abnormal electrical activity in the brain causes odd sensations and abnormal movement or behaviour. These are called convulsions or seizures. When a child has a seizure, there’s usually a temporary period of unconsciousness, a body convulsion, unusual movements or staring spells.

It can be hard to spot epilepsy in children with autism spectrum disorder (ASD) because some seizure symptoms can be similar to some ASD characteristics, like failing to respond to your name or doing repetitive, tic-like behaviour.

How common are seizures and epilepsy in children with autism spectrum disorder?
Epilepsy is quite common, and 20-30% of people with ASD also have epilepsy. Seizures are most common in children under five years and in teenagers.

People with ASD and moderate to severe intellectual disability, people with ASD and other neurological conditions (for example, cerebral palsy), or children who show regression are more likely to develop epilepsy.

There might also be  a genetic relationship between seizures and ASD.

How are seizures and epilepsy treated?
Treatment usually involves anti-epileptic medication. There are some steps you can take to minimise the effects of epilepsy. These include making sure your child takes medication on time, gets enough good-quality sleep and avoids situations that cause stress.

Find out more
Epilepsy Australia

Sleep problems

The most common sleep problems in children with autism spectrum disorder (ASD) are trouble falling asleep and staying asleep, nightmares, night terrors and sleepwalking.

How common are sleep problems in children with autism spectrum disorder?
Sleep difficulties are common among children with autism spectrum disorder (ASD). About two-thirds of children with ASD might have a sleep problem at some time.

How are sleep problems treated?
Good sleep hygiene can help. This includes:

  • cutting out drinks with caffeine in the afternoon and evening
  • getting sunshine and exercise throughout the day
  • getting rid of distractions like computers from the bedroom
  • having a regular bedtime routine.

You should always use these strategies at the same time as any other intervention.

Behaviour interventions can help, particularly for settling and night waking. Medication is another option, but health professionals generally recommend this only if behaviour interventions have failed. Melatonin is the only medication currently thought to be helpful.

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Tourette syndrome

Tourette syndrome is a brain disorder. People with Tourette syndrome have many movement-based tics and one or more vocal tics. These tics are sudden, repetitive and involuntary.

How common is Tourette syndrome in children with autism spectrum disorder?
About 4-5% of children with autism spectrum disorder (ASD) have Tourette syndrome and another 9-12% have tics of some kind. Tourette syndrome or motor tics are more common in children with moderate to severe intellectual disability.

How is Tourette syndrome treated?
Treatment for Tourette syndrome involves helping the person with the condition manage the tics. Psychobehavioural therapy, education, medication and reassurance can all help.

Find out more
Tourette Syndrome Association of Australia

Tuberous sclerosis

Tuberous sclerosis is a genetic disorder that causes abnormal growths in the brain and other vital organs. Symptoms can include white patches on the skin, facial rash, seizures, behaviour difficulties like hyperactivity, and intellectual disability.

How common is tuberous sclerosis in children with autism spectrum disorder? 
Tuberous sclerosis is not that common among children with autism spectrum disorder (ASD) (0-4%). It’s more common if the person also has a seizure disorder (8-14%).

How is tuberous sclerosis treated? 
Treatment focuses on managing symptoms and supporting the person and family.

Find out more
Australasian Tuberous Sclerosis Society

Getting help

If you think your child has another condition as well as autism spectrum disorder (ASD), talk with a health professional like your child’s GP, nurse or paediatrician. Depending on the condition, the professional might be able to order some tests, including a genetic test, or refer you to a specialist for further assessment.