Niemann-Pick disease (NPC) is an inherited metabolic disorder where lipids are not able to be metabolized adequately and hence build up and cause damage in various parts of the body such as the spleen, liver, lungs, bone marrow and brain. The different types of the disease are due to different genetic mutations.
There are four most commonly recognized forms of the disease: Types A, B, C, and D. Types A and B are also called Type I. Types C and D are also known as Type II.
Type C is a juvenile or subacute form of the condition which usually starts during childhood and survival into adulthood is possible.
- Difficulty in posturing of limbs (dystonia)
- Enlarged spleen
- Enlarged liver
- Jaundice at (or shortly after) birth
- Learning difficulties and progressive intellectual decline (dementia)
- Slurred, irregular speech
- Sudden loss of muscle tone which may lead to falls (cataplexy)
- Trouble moving the eyes up and down (vertical supranuclear gaze palsy)
- Unsteady gait, clumsiness, walking problems (ataxia)
Symptoms and disease progression of all forms of Niemann-Pick vary from person to person. No single symptom should be used to include or exclude Niemann-Pick as a diagnosis. Other, more common, diseases may cause symptoms similar to Niemann-Pick.
Niemann-Pick Type C occurs when the body can not properly break down cholesterol and other lipids (fats). This leads to too much cholesterol in the liver and spleen and excessive amounts of other lipids in the brain. There may be reduced ASM activity in some cells. Type C Niemann-Pick disease has been reported in all ethnic groups but it is most common among Puerto Ricans of Spanish descent.
All types of Niemann-Pick are autosomal recessive. This means that both parents are carriers -- they each carry one copy of the abnormal gene without having any signs of the disease themselves.
When both parents are carriers, there is a 25% chance that their child will have the disease and a 50% chance that a child will be a carrier.
Carrier detection testing is only possible if the specific genetic defect is identified. The defects involved in Types A and B have been extensively studied, and DNA tests for these forms of Niemann-Pick are available.
Genetic defects have been identified in the DNA of many patients with Type C, so it may be possible to diagnose those who carry the abnormal gene.
A few centers offer tests to diagnose a baby still in the womb.
A skin biopsy is usually used to diagnose Type C and Type D Niemann-Pick. Laboratory scientists will watch how the skin cells grow and study how they move and store cholesterol. DNA tests may also be done to look for the two genes that cause Niemann-Pick disease Type C.
Additional tests might include:
- Slit-lamp eye exam
- Liver biopsy or bone marrow aspiration
- Liver biopsy (usually not necessary)
- Sphingomyelinase assays
A child who shows signs of Type C before age 1 may not live to school age. Those who show show symptoms after entering school may live into their mid-to-late teens, with a few surviving into the 20s.
There is no specific treatment for Type C. A healthy, low-cholesterol diet is recommended, although research into low-cholesterol diets and cholesterol-lowering drugs does not show that these methods stop the disease from getting worse or change how cells break down cholesterol. However, medicines are available to control or relieve many symptoms, such as cataplexy and seizures.