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.