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Fragile X syndrome (FXS) is a genetic neurodevelopmental disorder characterized by mild-to-moderate intellectual disability. [1] The average IQ in males with FXS is under 55, while about two thirds of affected females are intellectually disabled.
Global developmental delay is an umbrella term used when children are significantly delayed in two or more areas of development. It can be diagnosed when a child is delayed in one or more milestones, categorised into motor skills, speech, cognitive skills, and social and emotional development. [1]
Down syndrome is a genetic condition in which people are born with an extra copy of chromosome 21. This extra copy affects the development of the body and brain, causing a range of physical and mental impairments for the individual. Fragile X syndrome, most frequent among males, is thought to cause autism and intellectual disability.
Macroorchidism is a disorder found in males, specifically in children, where a subject has abnormally large testes. The condition is commonly inherited in connection with fragile X syndrome (FXS), which is also the second most common genetic cause of intellectual disability. [1] The condition is also a rare sign of McCune–Albright syndrome. [2]
Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder most frequently seen in male premutation carriers of Fragile X syndrome (FXS) over the age of 50. [ 4 ] [ 5 ] The main clinical features of FXTAS include problems of movement with cerebellar gait ataxia and action tremor .
Those affected have a nearly normal life expectancy. [6] AS affects 1 in 12,000 to 20,000 people. [6] Males and females are affected with equal frequency. [7] It is named after British pediatrician Harry Angelman, who first described the syndrome in 1965. [7] [10] An older term, happy puppet syndrome, is generally considered pejorative. [11]
16p11.2 deletion syndrome is a rare genetic condition caused by microdeletion on the short arm of chromosome 16. Most affected individuals experience global developmental delay and intellectual disability, as well as childhood-onset obesity. [1] 16p11.2 deletion is estimated to account for approximately 1% of autism spectrum disorder cases. [3] [4]
Some classify the paternal age effect as one of two different types. One effect is directly related to advanced paternal age and autosomal mutations in the offspring. The other effect is an indirect effect in relation to mutations on the X chromosome which are passed to daughters who are then at risk for having sons with X-linked diseases. [57]