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Niemann-Pick disease types A and B occur when the body lacks enzymes needed to break down sphingomyelin.
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Niemann-Pick disease type C occurs when the body is not able to break down cholesterol and other lipids.
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Symptoms vary by type but may include intellectual disability and neurologic problems.
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The diagnosis is based on the results of prenatal screening tests, newborn screening tests (for types A and B), or biopsy of the liver.
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Niemann-Pick disease cannot be cured.
There are different types of inherited disorders. In Niemann-Pick disease, both parents of the affected child carry a copy of the abnormal gene. Because usually two copies of the abnormal gene are necessary for the disorder to occur, usually neither parent has the disorder. (See also Overview of Hereditary Metabolic Disorders.)
Sphingolipidoses occur when people do not have the enzymes needed to break down (metabolize) sphingolipids, which are compounds that protect the cell surface and serve certain functions in the cells. There are many types of sphingolipidoses besides Niemann-Pick disease types A and B:
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Gaucher disease (most common)
Types of Niemann-Pick disease
Niemann-Pick disease has several types. In types A and B, the deficiency of a specific enzyme called sphingomyelinase results in the accumulation of sphingomyelin (a product of fat metabolism). In type C, there is a defect in how fats (lipids) are moved around in a cell, resulting in accumulation of cholesterol and other fatty substances.
The most severe forms tend to occur in Ashkenazi Jewish people. The milder forms occur in all ethnic groups.
Children with type A (the most severe form) fail to grow normally and have several neurologic problems. These children usually die by age 2 or 3.
Children with type B develop fatty growths in the skin, areas of dark pigmentation, and an enlarged liver, spleen, and lymph nodes. They may be intellectually disabled.
Children with type C develop symptoms during childhood, with seizures and neurologic deterioration. Type C is always fatal, and most children die before age 20.
Diagnosis
Before birth, Niemann-Pick disease types A and B can be diagnosed in the fetus by using the prenatal screening tests chorionic villus sampling or amniocentesis.
After birth, the diagnosis of Niemann-Pick disease types A and B may be diagnosed in some states by routine newborn screening tests. Newborn screening tests cannot be done for type C.
Doctors also measure levels of sphingomyelinase in white blood cells for types A and B. Genetic testing, which is used to determine whether a couple is at increased risk of having a baby with a hereditary genetic disorder, is also available for all three types.
Tests of DNA (the building blocks of genes) may be done to identify carriers. Carriers are people who have an abnormal gene for a disorder but who do not have symptoms or visible evidence of the disorder.
Treatment
None of the types of Niemann-Pick disease can be cured, and children tend to die of infection or progressive dysfunction of the central nervous system (the brain and spinal cord).
Currently, some therapies that may slow or halt the progression of symptoms, such as bone marrow transplantation, stem cell transplantation, and enzyme replacement, are being studied.
