Lysosomals

Abstract

Lysosomal storage diseases (LSDs) are a group of more than 50 inherited metabolic disorders that result from defective lysosomal acid hydrolysis of endogenous macromolecules causing their accumulation (Winchester et al. 2000). A classification based on the nature of the primary stored material involved is reported in Table 52.1. Actually it is well known that all LSDs are not simply due to this storage, but they result from the perturbation of complex cell-signaling mechanisms. Generally lysosomal storage disorders occur when lysosomes do not function properly. All lysosomal storage diseases are single-gene/single-enzyme disorders resulting in lysosomal dysfunction. Various metabolic substrates are involved: lipids, glycoproteins, and mucopolysaccharides. Most of LSDs are autosomal recessively inherited disorders, with only three exceptions: Fabry disease and Hunter disease (MPS II) are X-linked recessive, while Danon disease is X-linked dominant. To date, in the absence of newborn screening programs, true LSD incidence is not known. Although some pilot projects reported a higher incidence (Spada et al. 2006; Chien et al. 2008), individual LSDs occur with an incidence of less than 1:100.000, while as a group the incidence is about 1:7,700 (Meikle et al. 1999). Comprehensive quali/quantitative analysis of the entire panel of accumulation products is still not available due to the complexity and chemical diversity of the storage products involved in LSDs.