What is an example of an autosomal recessive disorder?

An autosomal recessive disorder occurs when an individual inherits two copies of a mutated gene, one from each parent, leading to the expression of the disorder only when both alleles are recessive. PKU, or phenylketonuria, is a classic example of such a disorder. It is caused by a deficiency in the enzyme phenylalanine hydroxylase, which is necessary for the metabolism of the amino acid phenylalanine. When children with PKU consume phenylalanine, it accumulates in their system, potentially leading to severe cognitive impairment and other health issues if not managed through dietary restrictions.

Understanding this concept is pivotal, as PKU illustrates how genetics and inheritance patterns can profoundly affect health and development. In contrast, conditions like hemophilia and red-green color blindness are linked to chromosomal abnormalities on the sex chromosomes (X-linked), while polydactyly is typically associated with a dominant allele that can manifest with just one copy. This reinforces the uniqueness of PKU as an autosomal recessive disorder, emphasizing the necessity of both alleles being mutated for the condition to present in an individual.