More than 6,000 single-gene disorders leave a footprint that can now be tracked in an individual's DNA, according to information provided by the Human Genome Project. These disorders include cystic fibrosis, sickle cell anemia, Marfan syndrome and Huntington's disease.

This cavalcade of conditions can be overwhelming and frightening, especially when a health family tree makes it clear that certain medical risks hang a little too close to one's own branch.

Those concerned about risks can locate genetic counselors through the National Society of Genetic Counselors, at (The group offers its own free, Web-based family history tool at Family history guidelines are also available at But don't buy more life insurance just because a great-uncle's condition looks worrisome: There is considerable research showing that individuals tend to overestimate their risk of developing a condition in the family. This is particularly true for cancer and Alzheimer's disease.

If it's been a long time since you took a science class, don't despair. Simply put, the genes in your DNA provide blueprints for the production of proteins that build and operate cells. Genes live in chromosomes that are stored in each cell of the human body.

Problems can arise when genes carry mutations. Half of a child's genes come from each parent, so genetic counselors emphasize that it is especially crucial to determine if two potential parents are at risk to pass along the same mutation.

Francis Collins, director of the National Human Genome Research Institute, acknowledged that "people's concerns about getting diseases may be heightened" when collecting data for a family medical history but that "the benefits outweigh the short-term anxieties. We want to inspire action, not anxiety, but if a little fear gets people to talk to their doctor about a risky medical condition, that's a good thing." In any case, Collins said, whether or not individuals investigate and record their medical histories, the conditions persist, with more serious repercussions possible as time passes.

-- Alison Buckholtz