When you scan your family tree for disease, be sure to check the branch beside you. Because siblings share both genetics and childhood lifestyle factors, their health histories can reveal common at-risk areas that can’t be uncovered based on parents’ pasts alone, says Robin Bennett, a genetic counselor at the University of Washington Medical Center. Find out what health conditions your brother or sister has battled and schedule an appointment with your doctor to discuss what preventive action you should take. Here are five common conditions and your relative risk.

HEART DISEASE. If any of your brothers or sisters has heart disease before age 55, plaque is twice as likely to take hold inside your arteries.

PROSTATE CANCER. A brother with prostate cancer makes you three times more likely to develop a growth in your gland.

TYPE 2 DIABETES. Your risk of developing type 2 diabetes goes up by 30% if one of your siblings has the disease.

COLON CANCER. When colon cancer pops up in a sibling, your odds of producing a polyp double.

GLAUCOMA. A brother or sister with glaucoma increases your overall risk to this potentially blinding eye condition by 10%.

Percentage of American children and adults who will be obese by 2044 and 2058, respectively, if the rise in obesity continues at current rates.

Source: University of Missouri-Columbia study

Number of Americans who are currently afflicted with age-related macular degeneration.

Source: National Eye Institute