Niemann-Pick Disease - Sphingomyelinosis

Test Overview:

Niemann-Pick disease (NPD) is a type of lysosomal storage disease.  Two types of NPD have been discovered in cats, Niemann-Pick disease type A (NPA) and Niemann-Pick disease type C (NPC). Both are due to the accumulation of certain lipid substances within storage vesicles within the cells of the body.  The two types occur due to different genetic mutations, and cause slight differences in the age of onset of disease and the signs that may be seen, however there are many similarities between the two types.  The genetic mutation for NPC (on the NPC1 gene) has been characterised in cats.  Niemann-Pick disease is seen in the Siamese and domestic cat, and has been documented occasionally in other breeds, such as the Balinese. Because the cells cannot excrete the accumulating lipid product/s, the increasing amount and space that it takes up inside the cell causes progressive loss of cell function.  This results in a progressive disease that usually starts from 3-4 months of age (although it can be a little later) and generally results in death by the age of a year or so.  Signs are generally due to the effects on the cells of the brain, and may include ataxia, high stepping, head bobbing and/or a tremor of the head, a wide-based stance and loss of balance progressing to weakness, an inability to eat or drink properly, falling over and loss of mobility and often stiffness in the limbs and possible seizures.  Some cats display a characteristic chewing motion, and the liver and spleen may be severely enlarged.  Other cats may display paralysis and muscle weakness as the dominant clinical signs. Niemann-Pick disease has no cure.  Diagnosis is through laboratory examination of tissues such as liver and brain as part of a post-mortem examination to test for deficiency of the sphingomyelinase enzyme in the storage vesicles of the cells.  A genetic test for NPC is available, but not as yet for NPA.