The basics of lysosomal storage diseases Abstract. Lysosomal storage diseases are comprised of a group of more than 50 genetic disorders which are characterized by a defective lysosomal function. The lysosome is the recycling plant of the cell. Most of the lysosomal storage diseases are caused by a deficient hydrolase. The disturbed metabolism leads to accumulation of complex molecules. The classic classification is by the main storage molecule: Sphingolipidoses, Mucopolysaccharidoses and Glycoproteinosis. The modern classification stretches the definition and includes every disease that has a defect in a lysosomal component, which is needed for the normal function of the lysosome. That component includes lysosomal membrane proteins, activator proteins, transport proteins or non-lysosomal proteins. Lysosomal storage disease are rare diseases with a total incidence of 16 cases in 100'000 live births. Results of screening studies are hinting an underestimation of the real incidence. The most frequent lysosomal storage diseases are Gaucher's disease and Fabry's disease, two Sphingolipidoses. The similarity respective the symptoms of lysosomal storage diseases are the systemic manifestations and common cerebral involvement. The occurrence of the symptoms in the different lysosomal storage diseases are very different. The pathophysiological processes are versatile, the simple concept of overload and consecutive destruction of the cell is overdue. Over time a number of therapeutic approaches have been introduced: the substitution of the enzyme by enzyme replacement therapy, gene therapy or hematopoietic stem cell transplantation, stabilizing of the defective enzyme by pharmacologic chaperone or the decrease of the substrate by substrate reduction therapy.