Which abnormality of the sex chromosomes is the major cause of mental retardation and is linked to infantile autism?

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Fragile-X syndrome is caused by a mutation in the FMR1 gene, which leads to the inability to express certain proteins important for brain development and function. This syndrome is the most common genetic cause of mental retardation, affecting primarily males. It is also strongly linked to infantile autism, with up to 30% of individuals with fragile-X syndrome exhibiting autistic characteristics. Turner's syndrome and Klinefelter's syndrome are both chromosomal abnormalities that can affect physical development but do not typically result in mental retardation. Down syndrome is caused by an extra copy of chromosome 21 and can lead to intellectual disability, but it is not strongly linked to infantile autism.

Which Abnormality of the Sex Chromosomes Is the Major Cause