Estimating cumulative point prevalence of rare diseases: analysis of the Orphanet database

Abstract

Rare diseases, an emerging global public health priority, require an evidence-based estimate of the global point prevalence to inform public policy. We used the publicly available epidemiological data in the Orphanet database to calculate such a prevalence estimate. Overall, Orphanet contains information on 6172 unique rare diseases; 71.9% of which are genetic and 69.9% which are exclusively pediatric onset. Global point prevalence was calculated using rare disease prevalence data for predefined geographic regions from the 'Orphanet Epidemiological file' (http://www.orphadata.org/cgi-bin/epidemio.html). Of the 5304 diseases defined by point prevalence, 84.5% of those analysed have a point prevalence of <1/1 000 000. However 77.3-80.7% of the population burden of rare diseases is attributable to the 4.2% (n = 149) diseases in the most common prevalence range (1-5 per 10 000). Consequently national definitions of 'Rare Diseases' (ranging from prevalence of 5 to 80 per 100 000) represent a variable number of rare disease patients despite sharing the majority of rare disease in their scope. Our analysis yields a conservative, evidence-based estimate for the population prevalence of rare diseases of 3.5-5.9%, which equates to 263-446 million persons affected globally at any point in time. This figure is derived from data from 67.6% of the prevalent rare diseases; using the European definition of 5 per 10 000; and excluding rare cancers, infectious diseases, and poisonings. Future registry research and the implementation of rare disease codification in healthcare systems will further refine the estimates.

Fig. 1

Representation of epidemiological data in the Orphanet database

Fig. 2

Selection process of point prevalence data from the Orphanet database’s epidemiological file for analysis

Fig. 3

Distribution of inheritance patterns of genetic rare diseases. Genetic diseases were those in the ‘Orphanet classification of genetic diseases’, at the clinical entity ‘disorder’ level (excluding disorder groups and disorder subtypes)

Fig. 4

Distribution of rare diseases and rare disease patients according to the point prevalence class. For each prevalence class both the number of rare diseases and the range of patients with rare diseases are shown. The inclusivity of each prevalence class in national definitions of ‘rare disease’ is shown below