Lysosomal disease

Abstract The lysosome is a ubiquitous, single membrane-bond intracellular organelle which continuously recycles biological macromolecules: it not only breaks down cell components but has a dynamic role in nutrient and energy sensing that, through regulatory signalling, is critical for homeostasis and metabolic economy of the cell. More than 80 lysosomal diseases caused by single gene defects are known. Biochemical classification identifies (1) sphingolipidoses; (2) mucopolysaccharidoses; (3) glycoproteinoses; (4) glycogenosis, with or without lysosomal debris derived from subcellular organelles due to impaired autophagy; and (5) miscellaneous conditions with multiple classes of storage material such as the neuronal ceroid lipofuscinoses. Functional classification describes deficiency of (1) a specific acid hydrolase activity, (2) an activator protein, (3) a lysosomal membrane protein or transporter, or (4) abnormal post-translational modification of lysosomal proteins, and (5) abnormal biogenesis of lysosomes. A unified classification will emerge from genetic characterization integrated with clinicopathological manifestations of the individual disorders. Fabry’s and Gaucher’s diseases (glycosphingolipidoses) are probably the most frequent in the general population, but certain lysosomal diseases are over-represented in particular groups where consanguinity or endogamy is high. Other diseases discussed in this chapter include (1) cystinosis, (2) the mucopolysaccharidoses, (3) Pompe’s disease (glycogen storage disease type II), (4) Niemann–Pick diseases, (5) lysosomal acid lipase deficiency, (6) Danon’s disease, and (7) diseases more recently attributed to primary defects in lysosomes and related organelles.