Which genetic or chromosomal abnormality below is correctly described?

Question

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Phenylketonuria is an autosomal recessive genetic disorder where the child is unable to produce the enzyme phenylalanine hydroxylase, leading to a buildup of phenylalanine and other toxic substances in the body, which can cause intellectual disabilities if left untreated.

B, C, and D are all incorrect descriptions of the respective disorders. In Tay-Sachs disease, the body fails to produce an enzyme necessary to break down a fatty substance in nerve cells, leading to an accumulation in the brain and nervous system that causes progressive damage. In Down syndrome, a person has an extra copy of chromosome 21, which can cause developmental delays and intellectual disability, but does not result in cortical degeneration or death. And sickle-cell anemia is caused by a mutation in the hemoglobin gene that results in the production of abnormal red blood cells that can cause pain, organ damage, and other health problems, but is not related to an extra chromosome or mental retardation.

Which Genetic or Chromosomal Abnormality Below Is Correctly Described