Generally speaking, adults with intellectual disabilities (ID) experience high rates of morbidity; Furthermore, they have specific and sometimes more complex needs than ordinary patients. In its latest report on disability, the World Health Organization suggested that some of the disparities noted in care for this population could be attributed to the limited accessibility of health services and their low quality of care [1].

Intellectual disability is a concept that comes up quite often in general medicine and even more so in psychiatry [2]. Faced with a pathology, in patients with an intellectual disability, the psychiatrist or psychologist must call on more or less adapted behavioral knowledge. ID, formerly called mental retardation, is characterized by below-average intelligence or mental ability and a lack of skills necessary for daily living [3]. People with developmental disabilities can and do learn new skills, but they learn them more slowly. There are varying degrees of intellectual disability, from mild to profound. The term "mental retardation" is no longer used because it is offensive and has a negative connotation. According to the Diagnostic and Statistical Manual of Mental Disorders – Fifth Edition (DSM-5), diagnostic criteria for ID include a change in the definition of adaptive limitations [4]. The new criteria require that a deficiency be present in one adaptive domain rather than in two or more skill types. On the other hand, these patients are presenting serious behavior problems (SBP), which means behaviors which are self-injurious, assaultive, or cause serious property damage. Sixty-two percent of the ID population had a behavior problem (self-injurious, stereotyped, or aggressive/destructive behavior) and 18.7% had a behavior problem identified as challenging behavior, resulting in a prevalence of 80.3 per 100,000 in the base population [5]. This article aims to better understand what intellectual disability is for practical purposes in consultation.

The first step is a risk assessment to determine whether the patient's behavior poses a danger to themselves or others to determine the urgency and how best to proceed with the medical evaluation [6]. It is then necessary to determine whether a physical health diagnosis or a medication side effect is responsible for the problem. A medication inventory should be carried out, including recent changes and side effects. A complete history of the presenting problem behavior with the patient is taken by the caregiver, using appropriate engagement and communication strategies [7], which should include characteristics of the behavior, such as frequency, intensity or disturbance, duration, location and description of the habitual behavior disorder [8].

This will be followed by a physical examination focusing on the most common causes of serious behavioral disorders in this population. Experience shows that gastrointestinal disorders are common and often ignored (gastroesophageal reflux, gastritis, constipation) [9]. It is also necessary to systematically search for possible dental, ear infections, sinusitis or gynecological (painful periods) causes as well as other sources of painful manifestations [10] that may remain unnoticed due to the verbal communication difficulties of these patients. Pain hetero-assessment questionnaires can also be useful for diagnosing and documenting a painful etiology of serious behavioral disorders as well as for monitoring the effect of an analgesic prescription [11].

A person with an intellectual disability has limitations in two areas. These areas are:

• Intellectual functioning. Also known as IQ, which refers to a person's ability to learn, reason, make decisions, and solve problems.
• Adaptive behaviors. These are skills necessary for everyday life, such as being able to communicate effectively, interact with others, and take care of yourself.

IQ (intelligence quotient) is measured by a test. The average IQ is 100, with the majority of people having a score between 85 and 115. A person is considered intellectually disabled if they have an IQ below 70 to 75 [12].

To measure a child's adaptive behaviors, a specialist will observe the child's skills and compare them to other children of the same age. Things that can be observed include how well the child can feed or dress himself; to what extent is the child able to communicate and understand others; and how the child interacts with family, friends, and other children of the same age [13]. Intellectual disability is thought to affect around 1% of the population. Among those affected, 85% have a mild intellectual disability. This means they are a little slower than average to learn new information or skills. With good support, most will be able to live independently as adults [14].

Any time something interferes with normal brain development; intellectual disability can result. However, a specific cause of intellectual disability can only be identified about a third of the time [15].

The most common causes of intellectual disability are:

• Genetic causes: these include diseases like Down syndrome and Fragile X syndrome, and many other lesser-known ones.
• Problems during pregnancy: things that can interfere with fetal brain development include alcohol or drug use, malnutrition, certain infections, or preeclampsia.
• Problems during childbirth: intellectual disability can occur if a baby is deprived of oxygen during delivery or is extremely premature.
• An illness or trauma: infections such as meningitis, whooping cough or measles can lead to intellectual disability. Severe head injuries, near drowning, extreme malnutrition, brain infections, exposure to toxic substances such as lead, can also be the cause.
• None of the above: in two-thirds of all children with intellectual disabilities, the cause is unknown [16].

SBP sometimes occurs because the physical and human environments do not meet the needs of the person. Support for caregivers may be insufficient or too restrictive. It is important to facilitate “enabling environments” to meet specific needs; this can reduce or eliminate SBP [17]. The best way to create a supportive environment is to conduct a comprehensive functional assessment of behavior and improve functional communication using appropriate supports (e.g. pictograms) [18]. To assess SPB there are several inventories used the one most validated is the German version of the Personality Disorder Severity-ICD-11 Scale using nominal response model [19].

Adults living with intellectual disabilities are more likely to experience abuse, trauma, and/or negative life experiences than the general population [20]. Additionally, adults who have experienced abuse express more SBP [21] because their low intellectual ability leads to difficulties with emotional self-regulation, a low stress tolerance threshold and unpredictable emotional reactions. All of these factors have a negative effect on mental health and can cause anxiety, panic, depressed mood, and post-traumatic stress symptoms with or without psychotic features (e.g., hearing voices, exhibiting dissociative states, or reliving traumatic experience). It is essential to screen for these negative experiences and abuse, past and present.

Once physical health, environmental problems, and life events have been assessed, treatment should only be initiated after an initial psychiatric diagnosis has been made [22]. However, it is important to remember in this regard that hallucinations or apparent delusions, rather than being symptoms of psychosis, may reflect behavior appropriate to intellectual delay, such as having imaginary friends or "personal" conversations, or even being associated with the re-experiencing of a past trauma. In general, psychotic disorders tend to be over diagnosed and mood and anxiety disorders are often under diagnosed [23].

In most cases, antipsychotic medication should not be prescribed for SBPs without a firm prior diagnosis of psychosis [24]. If there is evidence that SBPs are related to a psychiatric disorder, then a trial of drug treatment specific to the latter, targeting the key symptom cluster (e.g., anxiety, depressed mood) may be indicated. However, it is necessary to monitor the possible paradoxical effects of these treatments which are very common in this population. It is also necessary to periodically ask the question of reducing or interrupting these treatments (principle of deprescription), experience unfortunately shows that these treatments are likely to continue for years, cumulatively and without concern for potential interactions between them [25]. Therapy is mostly psychopharmacology but in addition or sometimes sole could be a behavioral approach [26].

As we said in the introduction, the existence in the population of people with ID of a multitude of possible causes for a given SBP poses problems for professionals and it is a question of trying to determine what can come from unmet physiological or psychological needs versus the presence of a psychiatric disorder or medical condition. To this end, doctors should keep in mind the main causes of a behavioral disorder: physical health problems (including side effects of medications), inadequate environment and support provided to the patient, and importance of lived experiences and psychiatric disorders. Note that in most cases, it is preferable to carry out a psychiatric evaluation only when problems in other areas have been investigated.