Analysing factors related to challenging behaviour

Is there a psychiatric disorder?

Psychiatric disorders often lead to unusual experiences and behaviour. This site does not describe individual psychiatric disorders in great detail. 

The most common psychiatric disorders in people with intellectual disabilities are: psychosis and schizophrenia, mood disorder, anxiety disorder, compulsive disorder, eating disorder, personality disorder, PDD, ADHD, PTSS, somatoform disorder, hypersexuality and pathological mourning.

The risk factors for a psychiatric disorder include a syndrome, epilepsy, neurological or physical conditions, adverse personal factors and adverse social conditions. Generally, a combination of personal factors, medical factors and external factors will be responsible for the development and perpetuation of a psychiatric illness. ⁴² ,  ⁴³

It is known that some syndromes may be associated with psychiatric problems. For example, velo-cardio-facial syndrome is associated with increased susceptibility to schizophrenia and psychosis, Williams syndrome and the fragile-X syndrome are frequently found in conjunction with anxiety disorders, and depression is more common in adults with Down syndrome.

Neurological problems can also be associated with psychiatric problems. An example is Parkinson's disease, which is associated with an increased susceptibility to depression.

Psychiatric conditions occur more often in people with intellectual disabilities than in the general population. This is true for both children and adults with intellectual disabilities.

Children

A major British study of 10,438 children between the ages of 5 and 15 found that 39% of the children with intellectual disabilities had a psychiatric diagnosis, compared with 8.1% of children without intellectual disabilities ⁴⁴ .
The majority of diagnoses were antisocial behaviour disorder, anxiety disorder, ADHD and PDD. The diagnosis of depression and psychosis was not made more frequently in these children.

A Dutch review of international articles on health problems in children with intellectual disabilities showed that 10% had autism ⁴⁵ . The prevalence of autism in the general population is 0.6% -1% ⁴⁶ . A study of 825 children (aged 4 to 18 years old) in Friesland with an intellectual disability found that 16.7% had autism ⁴⁷ . Oeseburg found that 10.9% of adolescents with an intellectual disability in the Dutch provinces of Groningen and Drenthe had been diagnosed with autism and that 14% had PDD-NOS ⁴⁸ . The same author found an association between mild PDD and somatic conditions: adolescents with a somatic condition are significantly more likely to have a diagnosis of PDD. ⁴⁹

Adults

Adults with intellectual disabilities are two to four times more likely to have a psychiatric disorder than people without intellectual disabilities ⁵⁰ , ⁵¹ , with the prevalence varying between 10% and 30% depending on the study ⁵² . This study from Deb shows that schizophrenia (more psychotic episodes) is 10 times more common. Risk factors were increasing age and the increase severity of a physical disability or illness.

In her study of 1023 adults with intellectual disabilities, Cooper found that psychosis was ten times more probable than in the general population ⁵³ . In this study, the increased probability was correlated with a visual impairment, smoking, or no epilepsy.

An Australian study found a lifetime probability of a psychiatric disorder of 31.7% in a sample of over 9000 people with intellectual disabilities; the probability for schizophrenia in particular was 5.2%. ⁵⁴

An Icelandic study in the open population of 256 adults with severe intellectual disabilities found a prevalence for autism of 21%. ⁵⁵