To the Editor.
—The cover and cover story Don Perlis and Jonathan1 present an interesting Augenblicksdiagnose ("eye-blink diagnosis").I could not have guessed that the boy was retarded. But told that he is, I am almost certain that he has phenylketonuria. The boy's complexion is much lighter than his father's, and the paleness of his eyes is especially striking. This is highly suggestive of phenylketonuria, although not pathognomonic.The metabolic block in phenylketonuria prevents phenylalanine from being converted to tyrosine. Toxic levels of phenylalanine accumulate and cause mental retardation. The resulting low levels of tyrosine, a melanin precursor, result in decreased melanin synthesis. The affected child is typically much fairer in complexion than other members of his family, though not as pale as an albino.Why was Jonathan not diagnosed and treated in infancy? Diet therapy is capable of greatly moderating the disease and resulting in normal or near-normal