intellectual disability intellectual disability intellectual disability (id), also known as general learning disability in the united kingdom and formerly mental retardation, is a generalized neurodevelopmental disorder characterized by significantly impaired intellectual and adaptive functioning. it is defined by an iq under 70, in addition to deficits in two or more adaptive behaviors that affect everyday, general living. intellectual functions are defined under dsm-v as reasoning, problem‑solving, planning, abstract thinking, judgment, academic learning, and learning from instruction and experience, and practical understanding confirmed by both clinical assessment and standardized tests. adaptive behavior is defined in terms of conceptual, social, and practical skills involving tasks performed by people in their everyday lives. intellectual disabilityother namesintellectual developmental disability (idd), general learning disabilitychildren with intellectual disabilities and other developmental conditions competing in the special olympicsspecialtypsychiatry, pediatricsdifferential diagnosisautism, adhd, fragile x, fetal alcohol syndrome, learning disabilityfrequency153 million (2015) 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. down syndrome and fragile x syndrome are examples of syndromic intellectual disabilities. intellectual disability affects about 2 to 3% of the general population. seventy-five to ninety percent of the affected people have mild intellectual disability. non-syndromic, or idiopathic cases account for 30 to 50% of these cases. about a quarter of cases are caused by a genetic disorder, and about 5% of cases are inherited. cases of unknown cause affect about 95 million people as of 2013. signs and symptoms intellectual disability (id) becomes apparent during childhood and involves deficits in mental abilities, social skills, and core activities of daily living (adls) when compared to same-aged peers. there often are no physical signs of mild forms of id, although there may be characteristic physical traits when it is associated with a genetic disorder (e.g., down syndrome). the level of impairment ranges in severity for each person. some of the early signs can include: delays in reaching, or failure to achieve milestones in motor skills development (sitting, crawling, walking) slowness learning to talk, or continued difficulties with speech and language skills after starting to talk difficulty with self-help and self-care skills (e.g., getting dressed, washing, and feeding themselves) poor planning or problem-solving abilities behavioral and social problems failure to grow intellectually, or continued infant childlike behavior problems keeping up in school failure to adapt or adjust to new situations difficulty understanding and following social rules in early childhood, mild id (iq 50–69) may not be obvious or identified until children begin school. even when poor academic performance is recognized, it may take expert assessment to distinguish mild intellectual disability from specific learning disability or emotional/behavioral disorders. people with mild id are capable of learning reading and mathematics skills to approximately the level of a typical child aged nine to twelve. they can learn self-care and practical skills, such as cooking or using the local mass transit system. as individuals with intellectual disabilities reach adulthood, many learn to live independently and maintain gainful employment. about 85% of persons with id are likely to have mild id. moderate id (iq 35–49) is nearly always apparent within the first years of life. speech delays are particularly common signs of moderate id. people with moderate intellectual disabilities need considerable support in school, at home, and in the community in order to fully participate. while their academic potential is limited, they can learn simple health and safety skills and to participate in simple activities. as adults, they may live with their parents, in a supportive group home, or even semi-independently with significant supportive services to help them, for example, manage their finances. as adults, they may work in a sheltered workshop. about 10% of persons with id are likely to have moderate id. people with severe id (iq 20–34), accounting for 3.5% of persons with id, or profound id (iq 19 or below), accounting for 1.5% of persons with id, need more intensive support and supervision for their entire lives. they may learn some adls, but an intellectual disability is considered severe or profound when individuals are unable to independently care for themselves without ongoing significant assistance from a caregiver throughout adulthood. individuals with profound id are completely dependent on others for all adls and to maintain their physical health and safety. they may be able to learn to participate in some of these activities to a limited degree. autism and intellectual disability intellectual disability and autism spectrum disorder (asd) share clinical characteristics which can result in confusion while diagnosing. overlapping these two disorders, while common, can be detrimental to a person's well-being. those with asd that hold symptoms of id may be grouped into a co-diagnosis in which they are receiving treatment for a disorder they do not have. likewise, those with id that are mistaken to have asd may be treated for symptoms of a disorder they do not have. differentiating between these two disorders will allow clinicians to deliver or prescribe the appropriate treatments. comorbidity between id and asd is very common; it was estimated that roughly 40% of those with id also have asd, and roughly 70% of those with asd also have id. more recently, research has indicated a prevalence of roughly 30% for id in individuals with asd. both asd and id require shortfalls in communication and social awareness as defining criteria. defining differences in a study conducted in 2016 surveying 2816 cases, it was found that the top subsets that help differentiate between those with id and asd are, "impaired non-verbal social behavior and lack of social reciprocity, restricted interests, strict adherence to routines, stereotyped and repetitive motor mannerisms, and preoccupation with parts of objects". those with asd tend to show more deficits in non-verbal social behavior such as body language and understanding social cues. in a study done in 2008 of 336 individuals with varying levels of id, it was found that those with id display fewer instances of repetitive or ritualistic behaviors. it also recognized that those with asd, when compared to those with id, were more likely to isolate themselves and make less eye contact. when it comes to classification id and asd have very different guidelines. id has a standardized assessment called the supports intensity scale (sis); this measures severity on a system built around how much support an individual will need. while asd also classifies severity by support needed, there is no standard assessment; clinicians are free to diagnose severity at their own judgment. causes further information: x-linked intellectual disability down syndrome is the most common genetic cause of intellectual disability. among children, the cause of intellectual disability is unknown for one-third to one-half of cases. about 5% of cases are inherited. genetic defects that cause intellectual disability, but are not inherited, can be caused by accidents or mutations in genetic development. examples of such accidents are development of an extra chromosome 18 (trisomy 18) and down syndrome, which is the most common genetic cause. digeorge syndrome and fetal alcohol spectrum disorders are the two next most common causes. however, there are many other causes. the most common are: genetic conditions. sometimes disability is caused by abnormal genes inherited from parents, errors when genes combine, or other reasons like de novo mutations in genes associated with intellectual disability. the most prevalent genetic conditions include down syndrome, klinefelter syndrome, fragile x syndrome (common among boys), neurofibromatosis, congenital hypothyroidism, williams syndrome, phenylketonuria (pku), and prader–willi syndrome. other genetic conditions include phelan-mcdermid syndrome (22q13del), mowat–wilson syndrome, genetic ciliopathy, and siderius type x-linked intellectual disability (omim: 300263) as caused by mutations in the phf8 gene (omim: 300560). in the rarest of cases, abnormalities with the x or y chromosome may also cause disability. tetrasomy x and pentasomy x syndrome affect a small number of girls worldwide, while boys may be affected by 49, xxxxy, or 49, xyyyy. 47, xyy is not associated with significantly lowered iq though affected individuals may have slightly lower iqs than non-affected siblings on average. problems during pregnancy. intellectual disability can result when the fetus does not develop properly. for example, there may be a problem with the way the fetus's cells divide as it grows. a pregnant woman who drinks alcohol (see fetal alcohol spectrum disorder) or gets an infection like rubella during pregnancy may also have a baby with an intellectual disability. problems at birth. if a baby has problems during labor and birth, such as not getting enough oxygen, they may have a developmental disability due to brain damage. the group of proteins known as histones have an essential part in gene regulation, and sometimes these proteins become modified and are prevented from working properly. when the genes responsible for the development of neurons are affected, it affects the brain and behavior in the individual. exposure to certain types of disease or toxins. diseases like whooping cough, measles, or meningitis can cause intellectual disability if medical care is delayed or inadequate. exposure to poisons like lead or mercury may also affect mental ability. iodine deficiency, affecting approximately 2 billion people worldwide, is the leading preventable cause of intellectual disability in areas of the developing world where iodine deficiency is endemic. iodine deficiency also causes goiter, an enlargement of the thyroid gland. more common than full-fledged congenital iodine deficiency syndrome (formerly cretinism), as intellectual disability caused by severe iodine deficiency is called, is mild impairment of intelligence. residents of certain areas of the world, due to natural deficiency and governmental inaction, are severely affected by iodine deficiency. india has 500 million people with a deficiency, 54 million with goiter, and 2 million with congenital iodine deficiency. among other nations affected by iodine deficiency, china and kazakhstan have instituted widespread salt iodization programs. but, as of 2006, russia had not. malnutrition is a common cause of reduced intelligence in parts of the world affected by famine, such as ethiopia and nations struggling with extended periods of warfare that disrupt agriculture production and distribution. absence of the arcuate fasciculus. diagnosis according to both the american association on intellectual and developmental disabilities and the american psychiatric association's diagnostic and statistical manual of mental disorders (dsm-iv), three criteria must be met for a diagnosis of intellectual disability: significant limitation in general mental abilities (intellectual functioning), significant limitations in one or more areas of adaptive behavior across multiple environments (as measured by an adaptive behavior rating scale, i.e. communication, self-help skills, interpersonal skills, and more), and evidence that the limitations became apparent in childhood or adolescence. in general, people with intellectual disabilities have an iq below 70, but clinical discretion may be necessary for individuals who have a somewhat higher iq but severe impairment in adaptive functioning. it is formally diagnosed by an assessment of iq and adaptive behavior. a third condition requiring onset during the developmental period is used to distinguish intellectual disability from other conditions, such as traumatic brain injuries and dementias (including alzheimer's disease). intelligence quotient the first english-language iq test, the stanford–binet intelligence scales, was adapted from a test battery designed for school placement by alfred binet in france. lewis terman adapted binet's test and promoted it as a test measuring "general intelligence". terman's test was the first widely used mental test to report scores in "intelligence quotient" form ("mental age" divided by chronological age, multiplied by 100). current tests are scored in "deviation iq" form, with a performance level by a test-taker two standard deviations below the median score for the test-takers age group defined as iq 70. until the most recent revision of diagnostic standards, an iq of 70 or below was a primary factor for intellectual disability diagnosis, and iq scores were used to categorize degrees of intellectual disability. since the current diagnosis of intellectual disability is not based on iq scores alone, but must also take into consideration a person's adaptive functioning, the diagnosis is not made rigidly. it encompasses intellectual scores, adaptive functioning scores from an adaptive behavior rating scale based on descriptions of known abilities provided by someone familiar with the person, and also the observations of the assessment examiner, who is able to find out directly from the person what they can understand, communicate, and such like. iq assessment must be based on a current test.