National Society of Genetic Counselors
This website provides many publications on genetic disorders as well as the ability to locate genetic counselors through their database.
Chromosome Deletion Outreach
This organization and website provides a clear description of many chromosome disorders including Down syndrome. It was founded by parents and continues to be run by parents who have children with chromosome disorders.
Your Genes, Your Health
A clear, concise website on Down syndrome inheritence, tests, causes, treatment, and symptoms. The causes section gives a concise description of the excess of chromosome 21 found in people with Down syndrome.
Chromosome 21, Genetics Home Reference
A references specifically dedicated to chromosome 21 and all possible health conditions related to chromosome 21.
The following organizations and websites have general helpful information about Down syndrome.