Lipidoses are genetic disorders, passed from parents to their children, characterized by defects of the digestive system that impair the way the body uses dietary fat. When the body is unable to properly digest fats, lipids accumulate in body tissues in abnormal amounts.
The digestion, storage, and use of fats (lipids) from foods are complex processes that involve hundreds of chemical reactions in the body. In most people, the body is already programmed by its genetic code to produce all of the enzymes and chemicals necessary to carry out these functions. These genetic instructions are passed from parents to their offspring.
People with lipidoses are born without the genetic codes needed to tell their bodies how to complete a particular part of the fat digestion and utilization process. In most of these disorders, the body does not produce a certain enzyme, or specialized chemical. Over 30 different disorders of fat metabolism are related to genetic defects. Some people can carry the gene for these defects, but be free of symptoms; although the defects are passed from parents to children, the parents often do not have the disorders themselves.
There is great variance in the symptoms, available treatments, and long-term consequences of these conditions. Some of the conditions become apparent shortly after the infant is born. In other lipid disorders, symptoms may not develop until adulthood. For most of the lipidoses, diagnosis is suspected based on symptoms and family history. Tests of blood, urine, and tissue can be used to confirm the diagnosis. Genetic testing can be used, in some cases, to identify the defective gene. Some of these disorders can be controlled with changes in the diet, medications, or enzyme supplements. However, for many of these diseases, no treatment is available. Some may cause death in childhood or contribute to a shortened life expectancy. This section focuses on some of the most common or most serious lipidoses.
Lipidoses are very rare. The number of people affected depends on the disease, but for many diseases incidence is as little as one in 40,000 people. Some diseases have a higher prevalence in specific populations.
Causes and symptoms
Wolman's disease is caused by a genetic defect with a recessive pattern of inheritance that results in a deficiency of an enzyme that breaks down cholesterol. This causes large amounts of fat to accumulate in body tissues. Symptoms begin in the first few weeks of life and include an enlarged liver and spleen, adrenal calcification (hardening of adrenal tissue due to deposits of calcium salts), and fatty stools.
No treatment is available.
Death generally occurs before six months of age.
There is no known way to prevent lipidoses. Couples who have family histories of genetic defects can undergo genetic testing and counseling to see if they are at risk for having a child with one of the lipidoses disorders. During pregnancy, cell samples can be collected from the fetus using amniocentesis or chorionic villi sampling. The results of these tests can indicate if the developing fetus has a lipidosis disorder.
Amniocentesis—A procedure performed at 16-18 weeks of pregnancy in which a needle is inserted through a woman's abdomen into her uterus to draw out a small sample of the amniotic fluid from around the baby for analysis. Either the fluid itself or cells from the fluid can be used for a variety of tests to obtain information about genetic disorders and other medical conditions in the fetus.
Chorionic villus sampling—A procedure performed at 10 to 12 weeks of pregnancy in which a needle is inserted either through the mother's vagina or abdominal wall into the placenta to withdraw a small amount of chorionic membrane from around the early embryo. The amniotic fluid can be examined for signs of chromosome abnormalities or other genetic diseases.
Lipids—Organic compounds not soluble in water, but soluble in fat solvents such as alcohol. Lipids are stored in the body as energy reserves and are also important components of cell membranes. Commonly known as fats.
Recessive—Refers to an inherited trait that is outwardly obvious only when two copies of the gene for that trait are present. An individual displaying a recessive trait must have inherited one copy of the defective gene from each parent.
X-linked—A gene carried on the X chromosome, one of the two sex chromosomes.
Lipidoses have a variety of different symptoms and progressions. There are treatments for some—but not all—lipidoses. Treating the symptoms is always an integral part of lessening the impact of the disease. If parents have one child with a lipidoses disorder and are considering
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National Organization for Rare Diseases. 55 Kenosia Avenue, PO Box 1968, Danbury, CT 06813-1968. (203) 744-0100 or 1-800-999-6673. Fax: (203) 798-2291. Web site: <www.rarediseases.org>.
Tish Davidson, A.M. Altha Roberts Edgren