What type of inheritance is Phenylketonuria (PKU) categorized under?

• A. Autosomal Recessive
• B. Autosomal Dominant
• C. X-Linked Recessive
• D. Epigenetic Inheritance

Answer: (A)

Phenylketonuria (PKU) is categorized as an autosomal recessive disorder. This means that an individual must inherit two copies of the mutated gene, one from each parent, in order to exhibit the symptoms of the disease. The gene responsible for PKU is located on chromosome 12, and in individuals who have PKU, there is a deficiency in the enzyme phenylalanine hydroxylase. This enzyme is critical for the metabolism of the amino acid phenylalanine.

In cases of autosomal recessive conditions like PKU, carriers, who possess only one mutated copy of the gene, typically do not exhibit any symptoms because they have one normal copy that can produce sufficient enzyme activity. Only when both alleles are mutated does the biochemical pathway fail, leading to the accumulation of phenylalanine which can cause neurological damage and intellectual disability if left untreated.

In contrast, autosomal dominant disorders require only a single mutated gene from one parent to express the disease phenotype. X-linked recessive disorders are typically expressed in males and carried by females, while epigenetic inheritance involves changes in gene expression without altering the DNA sequence itself. Each of these genetic mechanisms operates under different rules and implications for inheritance and expression, making PKU