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Classification of mental retardation
Last reviewed: 04.07.2025
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There are many author classifications of mental retardation, which are presented in the relevant publications. In the clinical and pathogenetic differentiation of mental retardation, it is advisable to divide it into the following groups:
- exogenously conditioned, hereditary forms of brain damage not primarily associated with the formation of the anatomical and physiological basis of intelligence;
- mild forms of mental retardation caused by genetic variability in normal intelligence.
The clinical taxonomy of mental retardation is based on the widely used concepts of “differentiated” and “undifferentiated” mental retardation.
The group of clinically differentiated mental retardation includes nosologically independent diseases for which mental retardation is only one of the symptoms, usually the most severe.
Classification of differentiated forms of mental retardation (G.S. Marincheva, M.S. Vrono, 1999).
Hereditary forms.
- Syndromes with multiple congenital anomalies.
- Chromosomal diseases.
- Genetic syndromes with unclear inheritance pattern.
- Monogenically inherited syndromes.
- Hereditary metabolic defects.
- Phacomatosis.
- Neurological and neuromuscular diseases with mental retardation. Exogenously caused forms of mental retardation.
- Fetal alcohol syndrome (fetal alcohol syndrome).
- Infectious embryofetopathies (rubeolar, toxoplasmosis, cytomegalovirus).
- Hemolytic disease of the newborn.
Mental retardation of mixed (hereditary-exogenous) nature.
- Microcephaly.
- Hydrocephalus.
- Craniosynostosis.
- Congenital hypothyroidism.
Clinically undifferentiated mental retardation is mental retardation that does not have a specific clinical-psychopathological and somato-neurological picture of the disease. This group includes relatively mild forms of intellectual disability that occur in families characterized by the accumulation of cases of mental retardation and the presence of microsocial conditions that contribute to their occurrence. Mixed genesis is possible, including a hereditary-determined low level of intellectual development and additional exogenous-organic effects at the early stages of ontogenetic development, which leads to aggravation of the manifestations of mental retardation.
Many cases of undifferentiated mental retardation, mild in their manifestations, are considered in childhood as a delay in mental development, in older age as borderline mental retardation or as an extreme version of a low intellectual level in biologically healthy individuals.
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