Prevalence of Diagnosed Primary Immunodeficiencies Diseases in France: Results From the French National Registry and the CEREDIH Network.

Primary immunodeficiency diseases (PID) encompass more than 200 different rare diseases that share at least two characteristics, inheritance and increased susceptibility to infections. The mechanisms imply different components such as B-cells, T-cells, phagocytes or complement, and more than 150 genes are known to be involved in PID. While several studies have analyzed specific PID, very little is known about the exact repartition of the different groups of deficiencies. To assess epidemiological characteristics of these heterogeneous diseases, the French National Reference Centre for PID (CEREDIH) was established in November 2005 and created a dedicated registry to determine the distribution of PID patients in France who are under care in expert University hospitals.

The CEREDIH set up a national network of 18 regional centres including 58 University hospitals medical departments with experience in the care of both children and adults patients with PID. Data collected relied on the European Society for Immunodeficiencies core dataset. Overall, regional and detailed prevalence for major PID groups, and improvement of diagnosis over time were assessed. Data provided by our registry were compared to the ones previously reported by other National registries.

At April 2009, The CEREDIH registry encompasses a total of 3,083 patients. The overall prevalence is 4.4 cases for 100,000 inhabitants based on 2,682 alive patients. A majority of cases are children. Median age (Q1-Q3) at diagnosis was 3.3 years (0.7-10.3). Predominantly B-cell immunodeficiencies are the most common diseases observed (43%), the proportion of Common Variable Immunodeficiency (CVID) being 14%. Predominantly T cell disorders and phagocytic disorders were observed in 38% and 19.2% of patients, respectively. The 2 main phagocytic disorders were severe congenital neutropenias (65%) and chronic granulomatous diseases (27.6%). Immunoglobulin replacement therapy was given in 42% of all registered patients, by intravenous or subcutaneous route in 74% and 26% of cases, respectively. A significantly heterogeneous distribution of PID was observed in distinct geographical areas with variation in prevalence by a factor of 3. For B-cell deficiencies, there is a steady increase of identified cases between 1984 up to 2000. Noticeably, incidences for predominantly T cell and for innate immune deficiencies are likely to reach prevalence. Overall prevalence in France is quite similar to the one observed in other countries that have built a PID national registry, although the methodologies used were somehow different. The proportion of CVID is lower than in other national registries previously reported.

These results suggest that, while detection and referral to expert centres is fairly adequate for children, it is not yet the case in France for adult patients. There are still a number of unrecognised patients with PID (or patients not referred to university medical centres) as depicted by the heterogeneous distribution of PID observed, also pinpointing to regional differences in patients' care. This analysis provides the basis for further studies in assessing causes for observed differences and for taking action to increase awareness of PID, notably in adults, at national and regional levels. The CEREDIH registry could be a useful tool for measuring improvements in access to care for French PID patients and referral to centres with expertise.

No relevant conflicts of interest to declare.