Lipid storage disorder

Lipid storage disorders (or lipidoses) are a group of inherited metabolic disorders in which harmful amounts of lipids (fats) accumulate in some of the body’s cells and tissues.^[1] People with these disorders either do not produce enough of one of the enzymes needed to metabolize lipids or they produce enzymes that do not work properly. Over time, this excessive storage of fats can cause permanent cellular and tissue damage, particularly in the brain, peripheral nervous system, liver, spleen and bone marrow.

Lipids are broadly defined as any fat-soluble (lipophilic), naturally occurring molecule, such as fats, oils, waxes, steroids (such as cholesterol and estrogen), sterols and others. Lipids are important parts of the membranes found within and between each cell and in the myelin sheath that coats and protects the nerves.

Inside the cells, lysosomes convert, or metabolize, lipids and proteins into smaller components to provide energy for the body.

Classification

Disorders that store this intracellular material are part of the lysosomal storage diseases family of disorders.

Sphingolipidoses

Many lipid storage disorder can be classified into the subgroup of sphingolipidoses, as they relate to sphingolipid metabolism. Members of this group include Niemann-Pick disease, Fabry disease, Krabbe disease, Gaucher disease, Tay-Sachs disease, Metachromatic leukodystrophy, multiple sulfatase deficiency and Farber disease. They are generally inherited in an autosomal recessive fashion, but notably Fabry disease is X-linked. Taken together, sphingolipidoses have an incidence of approximately 1 in 10.000. Enzyme replacement therapy is available to treat mainly Fabry disease and Gaucher disease, and people with these types of sphingolipidoses may live well into adulthood. The other types are generally fatal by age 1 to 5 years for infantile forms, but progression may be mild for juvenile- or adult-onset forms.

Some of the sphingolipidoses may alternatively be classified into either GM1 gangliosidoses or GM2 gangliosidoses. Tay–Sachs disease belongs to the latter.

Other

Other lipid storage disorders that are generally not classified as sphingolipidoses include fucosidosis, Schindler disease and Wolman disease.

Inheritance

Lipid storage diseases can be inherited two ways: Autosomal recessive inheritance occurs when both parents carry and pass on a copy of the faulty gene, but neither parent show signs and symptoms of the condition and is not affected by the disorder. Each child born to these parents have a 25 percent chance of inheriting both copies of the defective gene, a 50 percent chance of being a carrier, and a 25 percent chance of not inheriting either copy of the defective gene. Children of either gender can be affected by an autosomal recessive this pattern of inheritance.

X-linked recessive (or sex linked) inheritance occurs when the mother carries the affected gene on the X chromosome that determines the child’s gender and passes it to her son. Sons of carriers have a 50 percent chance of inheriting the disorder. Daughters have a 50 percent chance of inheriting the X-linked chromosome but usually are not severely affected by the disorder. Affected men do not pass the disorder to their sons but their daughters will be carriers for the disorder.

Diagnosis

Diagnosis of the lipid storage disorders can be achieved through the use of several tests. These tests include clinical examination, biopsy, genetic testing, molecular analysis of cells or tissues, and enzyme assays. Certain forms of this disease can also be diagnosed through urine testing which will detect the stored material. Prenatal testing is also available to determine if the fetus will have the disease or is a carrier.^[1]

Treatment

There are no specific treatments for lipid storage disorders, however, there are some highly effective enzyme replacement therapies for people with type 1 Gaucher disease and some patients with type 3 Gaucher disease. There are other treatments such as the prescription of certain drugs like phenytoin and carbamazepine to treat pain for patients with Fabry disease. Furthermore, gene thereapies and bone marrow transplantation may prove to be effective for certain lipid storage disorders.^[2] Diet restrictions do not help prevent the buildup of lipids in the tissues.^[1]

See also

• Xanthomatosis
• Niemann–Pick disease

References