Researchers Look at NPC Type C Prevalence in the United States

A recent study aimed to get a fuller picture of the prevalence of Niemann-Pick Disease Type C (NPC), an ultra-rare, progressive neurodegenerative disease caused by autosomal recessive mutations in the NPC1 or NPC2 genes.

The disease is heterogeneous and has nonspecific clinical symptoms, and is often misdiagnosed or undiagnosed. Premature death is common, with most patients dying between 10 and 25 years of age.

Using claims data, researchers sought to estimate the number of people in the United States who fell into 3 categories:

• Those diagnosed with an NPC diagnosis
• Those diagnosed with an NPC diagnosis and/or are treated off-label with miglustat for NPC
• Those likely to have NPC

To determine diagnoses of NPC and to see if off-label treatment were occurring, researchers used the open claims Symphony Integrated DataVerse (Symphony IDV) database to examine records from October 2015 to January 2020. Symphony IDV is a large longitudinal administrative claims database that sources billing-related data submitted by pharmacies, hospitals, outpatient facilities, and physician practices. It contains about 275 million active patients at any moment and captures approximately 92% of all drugs dispensed in the United States and outlying territories, representing about 85% of the population.

Cases of NPC were defined as any patients with an ICD-10 code of E75.242 (NPC) during the study period. To determine patients who were diagnosed who were also being treated off-label with miglustat, researchers included patients with documented miglustat use (NDC 43975–0310 or 10,148–0201) who did not have any claim with Gaucher disease or GM1 gangliosidosis during the study period.

To determine the third point of the study, published NPC incidence (1 per 89,000 live births) and expected mortality estimates were applied to the 2018 United States birth rate (11.6 per 1000) and population size (326.7 million).

For this study, 308 million unique individuals were represented in the Symphony IDV; of these, 294 individuals had an NPC diagnosis, yielding an identified NPC prevalence of 0.95 per million people.

Researchers also found that 305 individuals were diagnosed with NPC and/or were treated with miglustat without having a diagnosis for either Gaucher or GM1 gangliosidosis, yielding an NPC diagnosed or treated prevalence of 0.99 per million people.

Based on the published literature, there are an estimated 42 new NPC cases per year. Applying this number to the distribution of NPC type (based on age of neurologic symptom onset) and corresponding mortality estimates generates an estimated 943 prevalent cases of NPC, or 2.9 cases of NPC per million people in the United States.

The authors said to their knowledge it is the first published analysis of NPC US prevalence.

Reference

Burton BK, Ellis AG, Orr B, et al. Estimating the prevalence of Niemann-Pick disease type C (NPC) in the United States. Mol Genet Metab. 2021; (134) doi: 10.1016/j.ymgme.2021.06.011