There are a number of online databases containing detailed information on rare diseases.
Orphanet is a database dedicated to information on rare diseases and orphan drugs. Access is free of charge. It provides information on any disease that occurs less often than 1 in 2,000 in the population, whether genetic, auto-immune, infectious, cancers or diseases with no accurate diagnosis. It has most of the numerous rare diseases described in its database.
NORD is an American voluntary health organisation dedicated to helping people with rare diseases and assisting the organisations that serve them. It is committed to the identification, treatment, and cure of rare disorders through programmes of education, advocacy, research, and service. You will find access to support sites, general information, developmental drugs and a database of medical reports on more than 1,200 rare diseases.