Entries for individual diseases feature an up-to-date summary of the knowledge that is accumulating under headings such as description, clinical features, molecular genetics, pathogenesis, diagnosis and clinical management. Given the magnitude of the task and the rapid progress within the field, the summaries are a work-in-progress rather than an elegantly written review, but they are comprehensively referenced to original articles and reviews.

Hyperlinks from each citation connect to details in Entrez. For larger entries — and some are very large indeed — a distillation (MINI-MIM) and clinical synopsis are offered. Links from the NCBI main page lead to general educational material on genetic disease and the Human Genome Project.

Many genetic diseases are rare, and the Office of Rare Diseases at the National Institutes of Health is a clearinghouse for information on them. (In most cases, a rare disease is defined as one that affects fewer than 200 000 people in the United States.) The site is designed to inform patients and physicians of ongoing research, contacts and resources.

Other useful sites are www.geneclinics.com, which provides clinical information relating to testing for and managing inherited disorders, and www.modimes.org, which discusses common disorders. Visitors to www.geneticalliance.org will find a coalition of genetic support groups, while www.genetests.org offers a directory of laboratory tests.

In Canada, the Canadian Association for Rare Disorders was launched by Maureen Gaetz-Faubert of Lethbridge, Alta., after she was diagnosed with a rare connective-tissue disorder. This site sports links to numerous organizations and support groups and the organization itself provides information and electronic networking for families, physicians and researchers.