A biochemical marker for the diagnosis of a central nervous system leukodystrophic genetic disorder, e.g., Childhood Onset Ataxia and Central Nervous System Hypomyelination (CACH)/Vanishing White Matter Disease (VWM) has been discovered herein. Such a marker has been found in the cerebrospinal fluid (CSF) of such patients. A two dimensional gel electrophoresis/mass spectrometry or image analysis of stained transferrin isoforms approach revealed that patients with CACH/VWM have a pronounced deficiency of the basic asialo form of the transferrin compared to the amounts of asialotransferrin normally present in CSF from healthy controls or other CNS disorders. The acidic sialotransferrin isoform is not reduced in these disorders. The transferrin isoform abnormality described in the CSF of patients with CACH/VWM is unique and may be used as a clinical diagnostic biomarker. The rapid (48 hr) and efficient diagnosis of this disorder described herein will have great clinical utility.