Lysosomal Storage Disorders
What are Lysosomal Storage Disorders?
Lysosomal storage disorders (LSDs) are inherited disorders caused by a deficiency of specific enzymes that are normally required for the breakdown of certain complex carbohydrates known as glycosaminoglycans (GAGs). If a specific lysosomal enzyme is not present in sufficient quantities, the normal breakdown of GAGs is incomplete or blocked. The cell is then unable to excrete the carbohydrate residues and they accumulate in the lysosomes of the cell. This accumulation disrupts the cell's normal functioning and gives rise to the clinical manifestations of LSDs.
Types of LSDs
To date, the scientific community has identified nearly 50 types and subtypes of LSDs, and new types continue to be identified. Although the different types of LSDs are rare individually, when taken together they are estimated to affect about 1 in 7,700 births, making them a relatively common and significant health problem.
All LSDs are progressive, with the rate of progression, the severity of symptoms, and the organ systems affected varying between disorders and even within each disorder type. LSDs affect different body organs or systems including the skeleton and joints, eyes, heart, lungs, kidneys, skin, and frequently the central nervous system.
Diagnosis of LSDs
All LSDs are inherited in an autosomal recessive manner (both parents must be carriers of the abnormal gene), except Hunter syndrome (MPS II) and Fabry disease, which are X-linked recessive disorders. The highly variable clinical presentation and the rareness of each individual disorder frequently contribute to missed or delayed diagnosis. Diagnosis of an LSD is usually the result of a physician recognizing a pattern of the various presenting symptoms; a definitive diagnosis may take many years during which other possible conditions are assessed and excluded. Specialized laboratories offer the specific enzyme assays or mutation analyses, which confirm or rule out the diagnosis of an LSD.
Treatment Options for LSDs
At present, there are no known cures for LSDs. Progress, however, continues to be made toward finding treatment options that go beyond treating the multiple symptoms of the disease and aim to address the underlying causes. Today, bone marrow transplantation and enzyme replacement therapy are available treatment options for patients with certain types of LSDs. Additionally, the scientific community continues to conduct research in the hopes of meeting the needs of patients suffering from all types of this disorder.