What results from individuals with PKU who have two copies of a rare inactive allele?

• A. Accumulation of proteins
• B. Accumulation of glucose
• C. Pheylketones accumulation
• D. Metabolization of carbohydrates

Answer: (C)

Individuals with phenylketonuria (PKU) have a genetic mutation that affects the metabolism of the amino acid phenylalanine. Normally, phenylalanine is converted into tyrosine by the enzyme phenylalanine hydroxylase. When individuals possess two copies of a rare inactive allele for the gene that encodes this enzyme, the enzyme is either nonfunctional or present at very low levels. As a result, phenylalanine cannot be effectively converted, leading to its accumulation in the body.

This buildup of phenylalanine is significant, as it is toxic at elevated levels and can result in severe neurological deficits and intellectual disabilities if not managed properly with dietary restrictions. The accumulated phenylalanine is subsequently converted into phenylketones, which are then excreted in the urine. Therefore, individuals with PKU who have this genetic condition will experience an accumulation of phenylketones as a direct consequence of their inability to metabolize excess phenylalanine properly. This accumulation is what defines the metabolic disorder associated with PKU.