Niemann-Pick type C is a lysosomal storage disease triggered by certain mutations that occur in the NPC1 gene and the NPC2 gene. It is one of the rarest medical conditions known to mankind because it occurs in one out of 150,000 people. In most cases it affects children who are under 10 years old, but on the other hand, there are also cases in which it may occur in people who are well into their sixties.
Causes and Genetics
Most cases of Niemann-Pick type C disease are triggered by genetic mutations in the NPC1 gene. Only 5 percent of the cases are actually triggered by the genetic mutations which occur in the NPC2 gene. These differences classify the disease as subtypes C1 and C2, depending on the affected type of gene. Clinically, these two subtypes are very similar because they both involve excess of lipids such as the cholesterol. The NPC1 gene is in charge of encoding a protein located in the cell membranes and it regulates the movement of lipids inside the cells. When a person suffers from a deficiency of such protein the lipids and cholesterol get accumulated in abnormal amounts in the cell membranes. The NPC2 gene has a slightly similar role as it is in charge of encoding a protein which is meant to bind and transport cholesterol throughout the human body. There are also Niemann-Pick type A and type B diseases but they are clinically, genetically and biochemically different than the type C. In types A and B, an enzyme called acid sphingomyelinase is partially or completely absent from the cells inside the human body. The NPC1 gene involved in the mutations and the development of Niemann-Pick type C disease has a function of transporting large water-insoluble molecules throughout the endosomal lysosomal system inside the cells. It needs to work in close cooperation with the NPC2 gene which also transports certain types of molecules inside the cells. When the accumulation of lipids and cholesterol take place, the transport system described above cannot function properly anymore. Different types of glycolipids along with cholesterol have very important roles in the plasma membranes of the cells. For instance, cholesterol is one of the essential building blocks of different sorts of steroid hormones. Niemann-Pick type C disease is also associated with abnormal accumulation of glycosphingolipids in the central nervous system which may lead to the development of severe structural changes such as the formation of meganeurite and ectopic dendritogenesis.
Signs and Symptoms
There is a large number of signs and symptoms which may be associated with Niemann-Pick type C disease. Splenomegaly is a medical term for an enlargement of the spleen, hepatomegaly is a medical term for an enlargement of the liver, and hepatosplenomegaly is a medical term for an enlargement of both organs. The previously mentioned along with elevated bilirubin and prolonged cases of jaundice usually affect infants. The enlargement of the liver and spleen do not have to occur right away or they sometimes remain somewhat unnoticed for years. These features differentiate Niemann-Pick type C disease from other types of lysosomal storage diseases such as the Gaucher disease, Niemann-Pick type A disease and Niemann-Pick type B disease. Enlargement of the spleen and liver are usually not associated with any major medical complications. Niemann-Pick type C disease is frequently connected with progressive neurological complications which lead to early disability and death. There is a large number of neurological symptoms which may be a consequence of Niemann-Pick type C disease and these include stupor, mutism ,delusions, hallucinations, psychotic depression, major depression, as well as bipolar disorder. Furthermore, there may be progressive hearing loss, dementia, psychosis, abnormally small head, drooping of the upper eyelid, hypotonia, velocity dependent increase in muscle tone, action dystonia, abnormal movements or posture, sudden loss of muscle tone, sleep inversion, paralysis, saccadic palsy, downgaze palsy, upgaze palsy, generalized epilepsy, partial epilepsy, tremor, difficult in swallowing, slurred speech and unsteady walk with uncoordinated limb movements. Terminal cases of the disease involve severe dementia, loss of volitional movement and complete ophthalmoplegia.
Unfortunately, there is no efficient cure for individuals suffering from Niemann-Pick Type C disease, nor there are any known treatment options which can successfully deal with symptoms and signs of the disorder. Those who suffer from this disease need to be provided with as much supportive care as possible so that the overall quality of their lives can be improved as much as possible. There are known cases of people surviving into their seventies while still suffering from Niemann-Pick type C disease.
The lifespan of those who suffer from Niemann-Pick type C disease is commonly determined by the age at which the disease occurred. Infantile or antenatal onset of the disease usually ends fatally in the first few years of life. The later the disease occurs, the slower it will progress.