How many types of retinitis pigmentosa...

Three: There are three basic types that differ on their inheritance pattern (sex linked, recessive and autosomal dominate) and severity the recessive the most severe and the auto dom the least.

Many: There are several dozen inheritance patterns for this condition with varying intensity, time of vision loss and varying completeness of vision loss. The type is important to know to predict the course of each case and to advise them about heredity and having children.