Mental retardation (MR), also known as intellectual disability, is one of the most common neuropsychiatric disorders in infants, children and adolescents. Its prevalence in the general population is usually reported in the 1-3% range. Understanding its cause gives important benefits to the patient, his/her family, and the general practitioner. There is a diagnostic triad made up of intellectual functioning significantly below the mean, concurrent deficiencies in at least 2 areas of adaptive functioning, and onset before 18 years. This paves the way for MR to be scaled in different degrees and allows the distinction between intellectual and adaptive performance, and between adaptive and maladaptive behaviour. The suggested clinical approach comprises 6 main steps: 1) Family history, 2) personal history, 3) physical examination, 4) clinical diagnosis, 5) imaging and laboratory diagnostics, 6) diagnostic synthesis and follow-up. New technologies, such as array comparative genomic hybridisation (aCGH), are currently making a huge impact, shifting in many instances from a phenotype-first to a genotype-first approach. This emphasizes the need for a close collaboration between clinicians and laboratory professionals. The aim of clinical evaluation is to provide the best care for the patient, which relies on habilitation and counselling for his/her family.
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