Niemann-Pick disease (NPD) refers to a group of inherited metabolic disorders known as the leukodystrophies or lipid storage diseases in which harmful quantities of a fatty substance (lipids) accumulate in the spleen, liver, lungs, bone marrow, and the brain. Symptoms may include lack of muscle coordination, brain degeneration, learning problems, loss of muscle tone, increased sensitivity to touch, spasticity, feeding and swallowing difficulties, slurred speech, and an enlarged liver and spleen. There may be clouding of the cornea and a characteristic cherry-red halo develops around the center of the retina. The disease has 4 related types. NPD Type A, neurodegenerative form, occurs in infants. It is characterized by jaundice, an enlarged liver, and profound brain damage. In NPD Type A, insufficient activity of an enzyme called sphingomyelinase causes the build up of toxic amounts of sphingomyelin, a fatty substance present in every cell of the body.
DIAGNOSTIC TESTING AND CODING
NPD Type A is diagnosed by measuring the amount of acid sphingomyelinase (ASM) in white blood cells. The test can be done using a blood or bone marrow sample. Sphingomyelinase assays (analysis) can also be used. DNA tests can be done to diagnose carriers. Prenatal testing is available when a mutation is known to exist in the family.