US FOP prevalence higher than expected

[Author: Laura Cowen]

The prevalence of fibrodysplasia ossificans progressiva (FOP) in the US is higher than previously believed, according to research published in the Orphanet Journal of Rare Diseases.

Frederik Kaplan (University of Pennsylvania, Philadelphia, USA) and co-authors say that FOP prevalence estimates are often cited as 0.5 cases per million US residents, but calculation of this number has “been hindered by the rarity of FOP and the heterogeneity of disease presentation.”

In the current analysis, Kaplan and team estimated FOP prevalence using data from three leading US FOP treatment centers (University of Pennsylvania, Mayo Clinic, and University of California San Francisco), the International Fibrodysplasia Ossificans Progressiva Association (IFOPA) membership list, and the IFOPA FOP Registry.

They identified 373 unique patients, of whom 294 were not reported as deceased in any list.

Ten patients had missing data, but for the remaining 284, the average time since last contact was 1.5 years. Approximately one third of patients had not been in contact with either the treatment centers, membership list, or FOP registry for at least 1 year, with 18% not having contact for at least 3 years.

Given that the reason for lack of contact for some of these patients may be death, the researchers took this into account and estimated that 279 patients (excluding the 10 with insufficient data) were alive on the prevalence analysis date (July 2020).

Using the US Census 2020 population estimate of 329,992,681 on the analysis day, Kaplan et al calculated that the unadjusted FOP prevalence was 0.85 cases per million US residents.

They then adjusted the calculation to include the 10 patients with insufficient data, using either an average survival rate estimate of 98.4% or a conservative survival rate estimate of 92.3% (based on a Kaplan–Meier survival curve from a previous study).

In both calculations, the adjusted prevalence rate was 0.88 cases per million US residents, or 1 in 1.14 million people.

However, Kaplan and co-investigators say “it is highly likely that patients exist outside of this pooled dataset (e.g., patients who have not yet been diagnosed, patients who receive care through physicians who have not connected to the authors’ institutions, or patients who have not connected with the IFOPA).”

“This suggests that the incidence of 0.88 per million calculated here is likely an underestimate,” they write.

The authors conclude: “While this study shows that there has been some success in achieving patient care among qualified experts in the United States, work remains in order to ensure that patients are connected to national and local care networks.”

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