My father had Factor V Leiden[1], a mutation that increases blood clotting. He was hospitalized multiple times in his 30s, and died suddenly at age 50. After his first blood clot he was put on anti-coagulants and took them every day of his life.
There is a 50% chance to pass this mutation to your offspring, and I wanted to know whether I could be affected. I discovered that I did indeed inherit the same allele, and went to see a hematologist to discuss it. She advised that I not smoke and keep fit (unlike my father) and that I shouldn't worry about taking medication unless some evidence of blood clots appears. This was always a worry for me, not knowing whether I would suffer the same fate. When I sent my DNA to 23andme, I was 25 years old and wondering if I'd already lived half of my life. Getting the results and following up with a specialist gave me great relief and eliminated this worry pretty much entirely.