| Backgrounds and Objective Phenylketonuria is the most common autosomal recessive disorder of amino acid metabolism resulted from a deficiency in phenylalanine hydroxylase, the enzyme that converts phenylalanine to tyrosine. The block in phenylalanine degradation results in elevated levels of phenylalanine and its metabolites in blood and urine. If untreated, Phenylketonuria leads to mental retardation, behavior abnormalities, epilepsy and other neurological abnormalities. Through the early initiation of a phe-restrict diet, the phenotype of untreated PKU can be prevented or alleviated.Domestic works on PKU deal with a wide range of interest in clinical medicine, epidemiology, molecular biology and genetic study. However, the MR research on PKU is so poor that only conventional MRI techniques performed in PKU have been reported. On the contrary, several abroad studies have shown that there is no correlation between either neuropsychology or clinical stage of patient and white matter abnormality on MR imaging. Some authors observed that there was strongest relationship between MRI change and the biological control of PKU. Others showed no association between them.In this study, different MRI techniques was used in PKU patients who were less than 11 years old in an attempt to explain the origin of possible MRI findings, such as T2WI, FLAIR, DWI and localized 'HMRS. It could fill up the research blankness in this field and help to further clarify the pathophysiology in PKU. In addition, it will be helpful to provide a useful tool in clinical diagnosis and treatment fellow up for those patients with PKU.Materials and Methods Twelve patients aged no more than 11 years old with PKU confirmed by biochemical and clinical examination involved in this study. All 12 patients underwent cranial MR imaging on the 1.5 T MR system with spin-echo T2-weighted and FLAIR sequence. The generally WM abnormalities were graded by T2-weighted images according to their extension and severity and the correlative coefficient was calculated to investigate the relationship between MR score and IQ as well as blood Phe concentration at the time of MR imaging. Diffusion-weighted imaging was performed with SE EPI sequence with a single bipolar gradient in the X, Y and Z directions (b=0,1000s/mm2). Apparent diffusion coefficient of water (ADC, 10-3 mm2/s) in the X, Y and Z directions (ADC x ,Y, z ) was calculated in patients and matched health volunteer to approach the pathophysiology change in molecular level . Abnormal signal around the posterior horn of lateral ventricle on T2WI and the WM in coronal radiation were selected as region of interest. Proton spectroscopy was performed using a long TE localized PRESS sequence. The MR spectra were acquired from two different regions of interest in all patients and control subjects. The first ROI located in parieto-occipital WM.which appeared as abnormally increased signal intensity on T2WI images. The second ROI located in coronal radiata, an area predominantly with normal WM. Several cerebral metabolites (choline/cretine, NAA/cretine) were calculated to further characterize the nature of WM abnormalities visible on MR imaging in molecular level.Results Patchy areas of increased signal intensity were demonstrated on T2WI images in all untreated PKU. Those abnormalities usually located symmetrically in the parieto-occipital WM. There is no correlation between MR imaging grade and IQ or blood Phe concentration. The treated PKU children showed normal in WM. Those abnormalities demonstrated on conventional MRI were observed with even better contrast in the DWI images. The ADCx,y,z value of the lesion area in PKU patients is lower than that of the same area in normal controls with great significance. The meanADC of water measured in PKU lesions decreased by approximately 23% compared to the ADC calculated for the same volume of interest in controls. The anisotropy observed in the group of controls was not clearly observed in periventricular areas in the group of PKU patient. The MR spectra of patien...
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