Substrate reduction therapy offers an approach to treatment of certain

metabolic disorder A metabolic disorder is a disorder that negatively alters the body's processing and distribution of macronutrients, such as proteins, fats, and carbohydrates. Metabolic disorders can happen when abnormal chemical reactions in the body alter the ...

s, especially glycogen storage diseases and lysosomal storage disorders. In a storage disorder, a critical failure in a

metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell (biology), cell. The reactants, products, and Metabolic intermediate, intermediates of an enzymatic reaction are known as metabolites, which are ...

prevents cellular breakdown and disposal of some large molecule. If residual breakdown through other pathways is insufficient to prevent harmful accumulation, the molecule accumulates in the cell and eventually interferes with normal biological processes. Examples of lysosomal storage disorders include

Gaucher's disease Gaucher's disease or Gaucher disease () (GD) is a genetic disorder in which glucocerebroside (a sphingolipid, also known as glucosylceramide) accumulates in cells and certain organs. The disorder is characterized by bruising, fatigue, anemia, low ...

Tay–Sachs disease Tay–Sachs disease is an Genetic disorder, inherited fatal lysosomal storage disease that results in the destruction of nerve cells in the brain and spinal cord. The most common form is infantile Tay–Sachs disease, which becomes apparent arou ...

, Sandhoff disease, and Sanfilippo syndrome. In a metabolic or genetic pathway, enzymes catalyze a series of reactions. Each enzyme is regulated or mediated by one gene through its RNA and protein products. At each phase in the pathway, enzyme activity catalyzes a reaction in which a precursor molecule (the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

) is transformed into its next intermediate state. Failure of the metabolic pathway leads to accumulation of the substrate, with possible harmful effects. Substrate reduction therapy addresses this failure by reducing the level of the substrate to a point where residual degradative activity is sufficient to prevent substrate accumulation. __TOC__

Examples

. The disease occurs when harmful quantities of a

fatty acid In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an ...

derivative called a

ganglioside A ganglioside is a molecule composed of a glycosphingolipid (ceramide and oligosaccharide) with one or more sialic acids (e.g. N-acetylneuraminic acid, ''N''-acetylneuraminic acid, NANA) linked on the sugar chain. NeuNAc, an acetylated derivative ...

accumulate in the

nerve cell A neuron (American English), neurone (British English), or nerve cell, is an excitable cell that fires electric signals called action potentials across a neural network in the nervous system. They are located in the nervous system and help to ...

s of the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

. Gangliosides are

lipids Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins Vitamin A, A, Vitamin D, D, Vitamin E, E and Vitamin K, K), monoglycerides, diglycerides, phospholipids, and others. The fu ...

, components of cellular membranes, and the ganglioside GM2, implicated in Tay–Sachs disease, is especially common in the

nervous tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system. The nervous system regulates and controls body functions and activity. It consists of two parts: the central nervous system (CNS) comprising the brain ...

of the

. By manipulating the brain's metabolism of GM2 gangliosides, an effective therapy could potentially be developed. One experiment has demonstrated that, by using the enzyme

sialidase Exo-α-sialidase (, sialidase, neuraminidase; systematic name acetylneuraminyl hydrolase) is a glycoside hydrolase that cleaves the glycosidic linkages of neuraminic acids: : Hydrolysis of α-(2→3)-, α-(2→6)-, α-(2→8)- glycosidic link ...

, the genetic defect can be effectively bypassed and GM2 gangliosides can be metabolized so that they become almost inconsequential. If a safe pharmacological treatment can be developed, one that causes the increased expression of lysosomal sialidase in neurons, a new form of therapy, essentially curing the disease, could be on the horizon. Metabolic therapies under investigation for Late-Onset TSD include treatment with the drug OGT 918 (''Zavesca''). *

. Miglustat and eliglustat are substrate reduction therapies for Gaucher's disease, inhibiting the synthesis of glucosylceramide.

References

{{Reflist, 2 Applied genetics Medical genetics