INTELLECTUAL DISABILITY: EPIDEMIOLOGY

The prevalence (number of cases of a disease based on the population at the time) of Intellectual Disability (ID), formerly known as Mental Retardation, is estimated between 1 and 2.5% and the incidence (number of new cases per year) is estimated to be around 1.8%.

Recent data indicates a reduction in the prevalence of ID only in western populations, while the opposite trend is evident among people with low to middle range incomes. In more developed countries like Finland or the Netherlands, the prevalence of ID is currently less than 1% and can reach up to 6% in some countries of eastern Europe. Even in the more fortunate contexts, the morbidity rates remain significantly higher compared to the rates of schizophrenia or bipolar disorder, which remain in the field of neuropsychiatric conditions.

Environmental factors such as exposure to lead, iron deficiency or malnutrition, perinatal problems, and many other non-genetic conditions seem to have a predominant pathogenic role in these geographic areas.

The lack of adequate and consistent epidemiological data was one of the main reasons for exclusion of the last study conducted by the World Health Organization and the World Bank Burden of Disease. One consequence is that the ID still represents a relevant position today among the "hidden problems" of global health. Another consequence is that the gap between the offering of health services and the unmet needs of the intellectually disabled people has become incalculable.
The WHO Atlas for the ID, which was recently published, is in fact the world’s first general glance at this issue.It is the first complete report on the resources and conditions of care in 170 countries worldwide. It provides a comprehensive description of the terminology, the use of classification systems, the organization of funds, the models of assistance, the legislation, the dissemination of knowledge, the training, and the role of national and international organizations and sources of information and research, as well.