Phenylketonuria (PKU) is an autosomal recessive disorder that results in th
e accumulation of phenylalanine in the blood and soft tissues. Elevated lev
els of phenylalanine have neurotoxic effects on the developing brain, resul
ting in mental retardation. Early diagnosis and treatment limits the neurol
ogical damage. Magnetic resonance imaging (MRI) changes are seen in the whi
te matter on T-2 weighted imaging in many subjects. The severity of the cha
nges do not correlate with clinical measures of neurological health. The ch
anges correlate best with recent phenylalanine control. The levels of brain
phenylalanine concentration using magnetic resonance spectroscopy (MRS) ha
ve been shown not to correlate tightly with the blood phenylalanine concent
ration. The individual variation in the brain to blood phenylalanine is lar
ge. This individual variability may be responsible for different clinical o
utcomes in PKU subjects who have similar long-term blood concentrations of
phenylalanine. MRDD Research Reviews 1999;5:132-135. (C) 1999 Wiley-Liss, I
nc.