Intellectual disability (ID), also known as general learning disability in the United Kingdom and formerly mental retardation (MR), 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 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 from a persons parents. 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.
Family history of undescended testicles or other problems of genital development
Cryptorchidism occurs at a much higher rate in a large number of congenital malformation syndromes. Among the more common are Down syndrome, Prader–Willi syndrome, and Noonan syndrome. In vitro fertilization, use of cosmetics by the mother, and pre-eclampsia have also been recognized as risk factors for development of cryptorchidism.In 2008, a study was published that investigated the possible relationship between cryptorchidism and prenatal exposure to a chemical called phthalate (DEHP), which is used in the manufacture of plastics. The researchers found a significant association between higher levels of DEHP metabolites in pregnant mothers and several sex-related changes, including incomplete descent of the testes in their sons. According to the lead author of the study, a national survey found that 25% of U.S. women had phthalate levels similar to the levels that were found to be associated with sexual abnormalities.A 2010 study  examined the prevalence of congenital cryptorchidism among offspring whose mothers had taken mild analgesics, primarily over-the-counter pain medications including ibuprofen (e.g. Advil) and paracetamol (acetaminophen). Combining the results from a survey of pregnant women prior to their due date in correlation with the health of their children and an ex vivo rat model, the study found  that pregnant women who had been exposed to mild analgesics had a higher prevalence of baby boys born with congenital cryptorchidism.New insight into the testicular descent mechanism has been hypothesized by the concept of a male programming window derived from animal studies.