Mental Retardation and Inborn Errors of Metabolism

The most common metabolic disease, and the first one to be treated by diet, is phenylketonuria (PKU).  PKU is a genetic disease in which a mutation in the enzyme phenylalanine hydroxylase (PAH) results in the inability to properly metabolize phenylalanine (Phe) into tyrosine.

This metabolic error causes a build up of phenylalanine which is converted to phenylpyruvate which is toxic.  Left untreated it causes problems in brain development resulting in mental retardation, brain damage and seizures.  At birth, babies appear normal then slowly deteriorate.  Prior to 1960 untreated PKU was the leading cause of mental retardation in the united states PKU facts.

Because newborn infants are asymptomatic, screening is conducted and PKU positive infants are started on a low PKU diet that is life long.  Foods containing phenylalanine have warning labels and are ubiquitous in the grocery store.

It's wild that a simple test and diet has eliminated a major causee of mental retardation