SMPD1-associated Niemann-Pick disease (NPD) is an inherited disease in which the body cannot properly metabolize a certain fatty substance called sphingomyelin due to a deficient enzyme called acid sphingomyelinase. As a result, sphingomyelin builds up in the body, causing cells to die and making it harder for certain organs to work properly. Mutations in SMPD1 can cause either type A or type B NPD.
Niemann-Pick disease type A causes mental disability, loss of motor skills, and enlargement of the liver and spleen, among other symptoms. The disease is often fatal by the age of 2 or 3. Symptoms of Niemann-Pick disease type A usually begin within the first few months of life. By the age of six months, infants with the disease have difficulty feeding, display an enlarged abdomen, and will begin to lose the motor skills they have developed. Seizures and spastic movement are common. Most will not learn to sit independently, crawl, or walk. They have poor muscle tone and develop cherry-red spots in their eyes. Many have a yellow tinge to the skin and whites of the eye (jaundice). Intellectual and motor skills will progressively and rapidly decline. These children may show vomiting, irritability, lung infections, and difficulty sleeping.
Unlike type A, which is fatal in early childhood, people with NPD type B have a less severe course of the disease and often live into adulthood. The most common symptoms include an enlargement of the liver and spleen (hepatosplenomegaly), a progressive decline in lung function and repeated respiratory infection, and poor or slower physical growth leading to shorter stature. They typically have abnormal lipid levels in their blood, with low HDL cholesterol and high LDL and triglycerides. This can lead to coronary artery disease later in life. People with NPD type B may also have a decreased number of blood platelets, which are needed to form blood clots. These symptoms may not be present from birth, developing in late childhood or adolescence. People with NPD type B usually do not have the nervous system complications (i.e. loss of motor skills) found in type A, however some people with the disease develop symptoms that combine features of both type A and type B.
Niemann-Pick disease (including both types A and B) is thought to affect 1 in 250,000 people. Niemann-Pick disease type A occurs most frequently in Ashkenazi Jews, among whom 1 in 100 is a carrier. The disease is not limited to Ashkenazi Jews, however, and has occurred in people of all ethnicities. Type A is the most common form of Niemann-Pick disease, accounting for 85% of cases. Type B affects people of many different ethnicities. Cases have been reported in 29 countries. NPD type B is most common in the Maghreb region of North Africa, which includes Algeria, Morocco, and Tunesia.
Unfortunately there are no effective treatments for Niemann-Pick disease type A. Medical professionals can attempt to treat the symptoms through physical therapy, monitoring of nutrition, and medication to help sleep disorders. Such treatment cannot stop the decline caused by the disease, however.
There is no treatment to address the cause of NPD type B. However, individual symptoms such as high cholesterol can be addressed. Those with clotting problems may need blood transfusions while those with breathing problems may need supplemental oxygen. The person's diet will be monitored to ensure they are getting the proper nutrition for growth.
The prognosis for a person with Niemann-Pick disease type A is poor. It is a severe disease which is typically fatal by the age of 2 or 3. People with NPB type B often survive into adulthood, however lifespan will likely be affected.
A non-profit center within the Mount Sinai School of Medicine established to provide information and support for patients with types A and B Niemann-Pick disease, as well as to scientists and physicians interested in these disorders.