In this hypothetical pedigree, the cigarette smoking proband had myocardial infarction at age 31. His identical nonsmoking twin had no cardiac complaints. The family at the left side, was such a family of the older studies. Their cousins and nephews, however, never sought medical attention and were not included in any analysis. The left family may have additional risk factors for cardiovascular disease or the right family may have inherited a longevity gene of grandma.