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Lysosomal Storage Diseases (LSDs) (pronounced lis?’som?l ) are a group of approximately 40 rare inherited metabolic disorders that result from defects in lysosomal function[1]. Lysosomal Storage Diseases result when a specific organelle in the body’s cells – the lysosome – malfunctions.
Gaucher disease was the first of these disorders to be described, in 1882, followed by Fabry disease in 1898. In the late 1950s and early 1960s, de Duve and colleagues, using cell fractionation techniques, cytological studies and biochemical analyses, identified and characterized the lysosome as a cellular organelle responsible for intracellular digestion and recycling of macromolecules. This was the scientific breakthrough that would lead to the understanding of the physiological basis of the Lysosomal Storage Diseases. Pompe disease was the first disease to be identified as an LSD in 1963, with L. Hers reporting the cause as a deficiency of a-glucosidase. Hers also suggested that other diseases, such as the mucopolysaccharide storage diseases, might be due to enzyme deficiencies.
Lysosomal Storage Disorders are caused by lysosomal dysfunction usually as a consequence of deficiency of a single enzyme required for the metabolism of lipids, glycoproteins (sugar containing proteins) or so-called mucopolysaccharides. Individually, LSDs occur with incidences of less than 1:100.000, however, as a group the incidence is about 1:5000 – 1:10.000. Most of these disorders are autosomal recessively inherited, however a few are X-linked recessively inherited, such as Fabry disease and Hunter syndrome (MPS II).
The lysosome is commonly referred to as the cell’s recycling center because it processes unwanted material into substances that the cell can utilize. Lysosomes break down this unwanted matter via enzymes, highly specialized proteins essential for survival. Lysosomal disorders are triggered when a particular enzyme exists in too small an amount or is missing altogether. When this happens, substances accumulate in the cell. In other words, when the lysosome doesn’t function normally, excess products destined for breakdown and recycling are stored in the cell.
Like other genetic diseases, individuals inherit Lysosomal Storage Diseases from their parents. Although each disorder results from different gene mutations that translate into a deficiency in enzyme activity, they all share a common biochemical characteristic – all lysosomal disorders originate from an abnormal accumulation of substances inside the lysosome.
Lysosomal Storage Diseases affect mostly children and they often die at a young and unpredictable age, many within a few months or years of birth. Many other children die of this disease following years of suffering from various symptoms of their particular disorder. The symptoms of Lysosomal Storage Disease vary, depending on the particular disorder and other variables like the age of onset, and can be mild to severe. They can include developmental delay, movement disorders, seizures, dementia, deafness and/or blindness. Some people with Lysosomal storage disease have enlarged livers (hepatomegaly) and enlarged spleens (splenomegaly), pulmonary and cardiac problems, and bones that grow abnormally.
The lysosomal storage diseases are generally classified by the nature of the primary stored material involved, and can be broadly broken into the following: (ICD-10 codes are provided where available)
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