What Is Niemann-Pick Disease, SMPD1-Related (NPD)?
Niemann-Pick disease (NPD), SMPD1-Related 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 the SMPD1 gene can cause either the type A form or the type B form of NPD.
Niemann-Pick Disease Type A (NPD-A)
NPD-A causes intellectual disability, loss of motor skills, and enlargement of the liver and spleen, among other symptoms. The disease is often fatal by the age of two or three. Symptoms of NPD-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.
Niemann-Pick Disease Type B (NPD-B)
Unlike type A, which is fatal in early childhood, individuals with NPD-B have a less severe course of the disease and may 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. Individuals with NPD-B may also have a decreased number of blood platelets, which are needed to form blood clots. These symptoms are not always present at birth and may develop instead in late childhood or adolescence. Individuals with NPD-B usually do not have the nervous system complications (i.e., loss of motor skills) found in NPD-A, but some individuals with the disease develop symptoms that combine features of both NPD-A and NPD-B.
How Common Is Niemann-Pick Disease, SMPD1-Related?
The exact incidence of Niemann-Pick disease (including both NPD-A and NPD-B) is unknown but estimated to be 1 in 250,000 individuals. NPD-A is the most common form of Niemann-Pick disease, accounting for 85% of cases. NPD-A is more common in individuals of Ashkenazi Jewish descent, while NPD-B is most common in the Maghreb region of North Africa, which includes Algeria, Morocco, and Tunisia.
How Is Niemann-Pick Disease, SMPD1-Related Treated?
There are currently no effective treatments for NPD-A. Medical professionals can attempt to treat the symptoms through physical therapy, monitoring of nutrition, and medication to help sleep disorders. However, treatment cannot stop the decline caused by the disease.
There is no treatment to address the cause of NPD-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. Individuals with NPD-B should be monitored to ensure they are getting the proper nutrition for growth from their diet.
What Is the Prognosis for an Individual with Niemann-Pick Disease, SMPD1-Related?
The prognosis for an individual with NPD-A is poor. It is a severe disease that is typically fatal by the age of two or three. Individuals with NPD-B often survive into adulthood, but lifespan will likely be affected.