Deepak Gulati, MD
Smoking has been identified as the most important lifestyle risk factor for subarachnoid hemorrhage (SAH) and accounts for at least one third of all cases.
Familial risk is defined as the probability of a healthy family member being affected by the same disease that has already affected at least one other family member. Familial risk of SAH depends on a number of factors, including genetic and environmental factors. It has been a challenge to estimate the genetic risk of SAH in relatives given the relatively low incidence of SAH. The accurate estimation of genetic risk could have significant implications on prophylactic screening protocols of intracranial aneurysms. Large twin cohorts provide a “shortcut” to carry out the estimation of heritability. Twin studies usually provide the natural way to separate familial resemblance from genetic influence. The Nordic Twin Study in 2010 indicated that most twin pairs were discordant for SAH, i.e., only one twin died from SAH. However, the role of risk factors in explaining this discordance was not studied.