It is often difficult to estimate the prevalence of a rare disease within the United States. For one, it can be difficult to find all of the patients with a certain condition due to their rarity. Additionally, many rare diseases go undiagnosed or misdiagnosed, which could further skew the numbers.
A recent study published in Molecular Genetics and Metabolism aimed to find the prevalence of Niemann-Pick disease type C (NPC), an extremely rare neurodegenerative disease.
About Niemann-Pick Disease
Niemann-Pick disease is a group of rare and severe lipid storage disorders. It occurs when the body is unable to transfer sphingomyelin, a type of lipid, into the cells, causing them to accumulate in the lysosomes. This disease is divided into three types: A, B, and C. Between these types, severity, onset, and symptoms vary. Types A and B of this disease occur when there are mutations in the SMPD1 gene, which affects the activity of sphingomyelin. Type C, which was investigated in this study, is caused by mutations in the NPC1 or NPC2 genes, which are responsible for a protein that transports sphingomyelin. These genes are all inherited in an autosomal recessive pattern. Symptoms of Niemann-Pick disease vary depending on the type and location of the accumulation of sphingomyelin.
The liver and spleen are common places in which sphingomyelin accumulates, and symptoms would be a loss of appetite, an enlarged abdomen, low levels of platelets in the blood, and pain. If the central nervous system is affected, symptoms may be slurred speech, difficulty swallowing, impaired eye movements, and the loss of intellectual abilities. Bones are not as commonly affected, but when they are, people experience sleep-related disorders and enlarged bone marrow cavities. Type C is characterized by neurological abnormalities, like loss of coordination and difficulty speaking. Difficulty in swallowing is also common. Intellectual disabilities worsen over time. Cataplexy and seizures may occur as the disease progresses as well. Type C is also fatal, with most patients passing away between the ages of 10 and 25.
Treatment for this disease is dependent on the type, but they are all focused on managing symptoms. Anti-seizure, sleep-inducing, and anti-depression medications may all be prescribed.
About the Study
Using the Symphony Integrated DataVerse (Symphony IDV) database, researchers looked for people in the United States who likely have NPC, those diagnosed with NPC, and those diagnosed with NPC who are being treated off-label with miglustat. This database represents about 85% of the population, with data from around 275 million patients.
The researchers analyzed data from October 2015 to January 2020, in which they included 308 million people. Within these millions, 294 people had NPC, translating to a prevalence of 0.95 per million people. Beyond this, 305 people were discovered to be treated with miglustat without a GM1 gangliosidosis or Gaucher disease diagnosis, leading to a prevalence of 0.99 per million people.
Through an analysis of published literature, the researchers went on to estimate the number of new NPC cases each year, which was 42 cases. They then used this number to estimate the prevalence of NPC in the United States as a whole, which was 2.9 per one million people, or 943 overall cases.
According to the study authors, this is the first research of its kind to look into the prevalence of NPC.
Learn more here.