What is the genetic disorder involving an abnormality in the X chromosome called?

The genetic disorder that involves an abnormality in the X chromosome is Fragile X syndrome. This condition is the result of a mutation in the FMR1 gene located on the X chromosome, which leads to a variety of developmental issues, including intellectual disabilities and behavioral challenges. Fragile X syndrome is one of the most common inherited forms of intellectual disability and is more prevalent in males, who have only one X chromosome, compared to females, who have two.

The other conditions listed do not originate from abnormalities on the X chromosome. Hemophilia, while also an X-linked disorder, specifically relates to blood clotting deficiencies rather than a general chromosomal abnormality. Huntington's disease is caused by an autosomal dominant mutation on chromosome 4, and cystic fibrosis results from mutations in the CFTR gene on chromosome 7, making them unrelated to X chromosome abnormalities. Thus, Fragile X syndrome is correctly identified as the genetic disorder associated with an abnormality in the X chromosome.