What is the most common recognized biological cause of mental retardation?

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Down syndrome is caused by the presence of an extra copy of chromosome 21, resulting in developmental delays and intellectual disability. It is the most commonly recognized biological cause of mental retardation. PKU is a genetic disorder that can cause intellectual disability if left untreated, but it is not as common as Down syndrome. Lead poisoning can also lead to intellectual disability, but it is not the most common cause. Fragile X syndrome is a genetic disorder that can cause intellectual disability, but it is less common than Down syndrome.

What Is the Most Common Recognized Biological Cause of Mental