What is the result of untreated phenylketonuria (PKU)?

Untreated phenylketonuria (PKU) leads to brain damage due to the accumulation of phenylalanine, an amino acid that becomes toxic at elevated levels. Individuals with PKU have a deficiency in the enzyme needed to break down phenylalanine, resulting in its build-up, particularly in the brain. This accumulation can interfere with normal brain development and function, leading to cognitive impairments, developmental delays, and other neurological issues. Thus, the critical concern in PKU is the impact on brain health, which makes brain damage the most accurate result of untreated PKU.