[Epidemiology and prevalence of hereditary retinal dystrophies in the Northern France].

The authors present part of a study concerning inherited retinal dystrophies as recorded among the inhabitants of the Nord-Pas-de-Calais region of France. This retrospective study, covering eighteen years (from 1972 to 1989) and covering a population of nearly 4 millions inhabitants, has enabled us to assess the prevalence of each disease. 1,660 cases have been detected and 650 pedigrees have been established. The spatial distribution of the patients in reference to their places of origin in relation to the spatial division of area into "communes" or districts roughly corresponded to the population density and revealed a few centres of dominant retinal dystrophies in rural areas. The analysis of the distribution and inheritance of the various forms of retinitis pigmentosa confirmed the results obtained in other recent and similar studies carried out in other countries. The age pyramid of the detected cases followed that of the population under surveillance. Detection of all dystrophies increased up to the age of 35, then followed the normal decreasing pattern for older generations. As for retinoschisis, detection usually took place in the first fifteen years after birth; for Stargardt's disease, it has occurred up to the age of 20 and for Best's dystrophy, the process was the most extensive and the slowest to appear. The global number of dystrophies studied, corresponded to a prevalence of 1:1,490, which allowed us to estimate that the number of cases in France was 33,800. If we apply the phenomenon to all the populations of the European Community, we must consider that more than 300,000 patients are now affected by disabling hereditary retinal dystrophies.