Intellectual disability, also known as general learning disability, and mental retardation, is a generalized neurodevelopmental disorder characterized by significantly impaired intellectual and adaptive functioning.
Learning disability is a classification that includes several areas of functioning in which a person has difficulty learning in a typical manner, usually caused by an unknown factor or factors.
Intellect is a term used in studies of the human mind, and refers to the ability of the mind to come to correct conclusions about what is true or real, and about how to solve problems.
Adaptive behavior refers to behavior that enables a person to get along in his or her environment with greatest success and least conflict with others.
Disability Awareness: Intellectual Disability by National Center on Health, Physical Activity and Disability (NCHPAD)
It is defined by an IQ score under 70 in addition to deficits in two or more adaptive behaviors that affect everyday, general living.
What Is An Intellectual Disability? by EliteBehaviorMedia
Once focused almost entirely on cognition, the definition now includes both a component relating to mental functioning and one relating to individuals' functional skills in their environments.
Cognition is "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses".
As a result of this focus on the person's abilities in practice, a person with an unusually low IQ may not be considered to have intellectually disability.
Intellectual disability is subdivided into syndromic intellectual disability, in which intellectual deficits associated with other medical and behavioral signs and symptoms are present, and non-syndromic intellectual disability, in which intellectual deficits appear without other abnormalities.
A medical sign is an objective indication of some medical fact or characteristic that may be detected by a patient or anyone, especially a physician, before or during a physical examination of a patient.
Down syndrome and fragile X syndrome are examples of syndromic intellectual disabilities.
Down syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21.
Non-syndromic or idiopathic cases account for 30–50% of cases.
An idiopathy is any disease with unknown cause or mechanism of apparently spontaneous origin.
About a quarter of cases are caused by a genetic disorder, and about 5% of cases are inherited from a person's parents.
A genetic disorder is a genetic problem caused by one or more abnormalities in the genome, especially a condition that is present from birth.
Cases of unknown cause affect about 95 million people as of 2013.