Intellectual Disability/Intellectual Developmental Disorder

Intelligence and intellectual disability (ID) or intellectual developmental disorder (IDD), according to the most recent terminology, might not be natural kinds but the result of a historically contingent human attempt of self-definition and self-characterization. The seeds of intelligence as a measure for classifying humans were sown at the end of the twelfth century, with the expansion of towns and trades and the consequent onset of state and ecclesiastical administration while scientific attention toward ID/IDD started at the end of the eighteenth century, after the French and American revolutions had restored value to human freedom and dignity and declared principles of equality, natural, and imprescriptible rights. Different definitions and diagnostic criteria of ID/IDD have been provided across history in accordance with varying conceptualizations, passing from a unitary and scarcely defined model of “mental deficiency” to a group of lifespan conditions characterized by early onset of significantly below average intellectual functioning and adaptive behavior. ID/IDD represents a complex syndrome grouping (meta-syndrome), requiring a polynomious-polysemic approach to be named and defined for different audiences and purposes, including classification systems. The evolution of its diagnostic criteria attempted to maximize clinical consensus but masked a wide degree of heterogeneity between and within individuals for many aspects. Well-timed, sensitive, comprehensive, and interdisciplinary assessment represents a fundamental process to appropriately define overall health condition and profile of strengths, weaknesses, and needs of each individual with ID/IDD. The most relevant aspects for assessment include personal and medical history, the condition of ID/IDD itself (specific cognitive impairments, language, adaptive skills, functioning), current physical and mental status, behavioral profile, personal experiences, and quality of life.