Niemann-Pick type C is a lysosomal storage diseasetriggered by certain mutations that occur in the NPC1 gene and the NPC2 gene. Itis one of the rarest medical conditions known to mankind because it occurs in oneout of 150,000 people. In most cases it affects children who are under 10 yearsold, but on the other hand, there are also cases in which it may occur in peoplewho are well into their sixties.
Causes and Genetics
Most cases of Niemann-Pick type C disease are triggered bygenetic mutations in the NPC1 gene. Only 5 percent of the cases are actuallytriggered by the genetic mutations which occur in the NPC2 gene. Thesedifferences classify the disease as subtypes C1 and C2, depending on theaffected type of gene. Clinically, these two subtypes are very similar becausethey both involve excess of lipids such as the cholesterol. The NPC1 gene is incharge of encoding a protein located in the cell membranes and it regulates the movement of lipids inside the cells. When a person suffers froma deficiency of such protein the lipids and cholesterol get accumulated in abnormalamounts in the cell membranes. The NPC2 gene has a slightly similar role as itis in charge of encoding a protein which is meant to bind and transportcholesterol throughout the human body. There are also Niemann-Pick type A andtype B diseases but they are clinically, genetically and biochemicallydifferent than the type C. In types A and B, an enzyme called acidsphingomyelinase is partially or completely absent from the cells inside thehuman body. The NPC1 gene involved in the mutations and the development ofNiemann-Pick type C disease has a function of transporting largewater-insoluble molecules throughout the endosomal lysosomal system inside thecells. It needs to work in close cooperation with the NPC2 gene which alsotransports certain types of molecules inside the cells. When the accumulationof lipids and cholesterol take place, the transport system described abovecannot function properly anymore. Different types of glycolipids along withcholesterol have very important roles in the plasma membranes of the cells. For instance, cholesterol is one of the essential building blocks of different sorts ofsteroid hormones. Niemann-Pick type C disease is also associated with abnormalaccumulation of glycosphingolipids in the central nervous system which may leadto the development of severe structural changes such as the formationof meganeurite and ectopic dendritogenesis.
Signs and Symptoms
There is a large number of signs and symptoms which may beassociated with Niemann-Pick type C disease. Splenomegaly is a medical term foran enlargement of the spleen, hepatomegaly is a medical term for an enlargement ofthe 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 usuallyaffect infants. The enlargement of the liver and spleen do not have to occur rightaway or they sometimes remain somewhat unnoticed for years. Thesefeatures differentiate Niemann-Pick type C disease from other types oflysosomal storage diseases such as the Gaucher disease, Niemann-Pick type Adisease 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 neurologicalcomplications which lead to early disability and death. There is a large numberof neurological symptoms which may be a consequence of Niemann-Pick type Cdisease and these include stupor, mutism ,delusions, hallucinations, psychoticdepression, major depression, as well as bipolar disorder. Furthermore, there may be progressive hearing loss,dementia, psychosis, abnormally small head, drooping of the uppereyelid, 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, partialepilepsy, tremor, difficult in swallowing, slurred speech and unsteady walkwith uncoordinated limb movements. Terminal cases of the disease involve severedementia, 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 treatmentoptions which can successfully deal with symptoms and signs of the disorder. Those who suffer from this disease needto be provided with as much supportive care as possible so that the overallquality of their lives can be improved as much as possible. There are knowncases of people surviving into their seventies while still suffering fromNiemann-Pick type C disease.
The lifespan of those who suffer from Niemann-Pick type Cdisease is commonly determined by the age at which the disease occurred.Infantile or antenatal onset of the disease usually ends fatally in the firstfew years of life. The later the disease occurs, the slower it will progress.