Specific Objectives Draw a schematic diagram depicting the two categories of hereditary neurometabolic diseases. Summarize the similarities between the leukodystrophies and neuronal storage diseases, in terms of age of onset, inheritance patterns, and clinical findings. Many neurometabolic diseases are caused by genetically determined enzyme deficiencies localized to the lysosomes.
Lysosomal enzymes are necessary in the catabolism of the lipids of myelin and neurons.
Prenatal diagnosis can be established by enzyme assays on amniotic fluid. Due to absence of a particular lysosomal enzyme, an intermediate catabolic product accumulates excessively in the myelin. Subsequently, this chemically abnormal myelin disintegrates. Metachromatic leukodystrophy is a disorder of sulfatide, a cerebroside sulfate ester normally present in myelin. In the catabolism of myelin, the sulfatide is degraded into cerebroside and inorganic sulfate by the enzyme aryl sulfatase A. Aryl sulfatase A is missing in metachromatic leukodystrophy.