Background and Purpose--Previous studies of familial risks have often combined ischemic and hemorrhagic stroke even though it seems unlikely that these 2 very different pathological conditions are under the same genetic influence. This study is the first to investigate the concordant (same subtype) and disconcordant (different subtype) association between ischemic and hemorrhagic stroke.

Methods--Data of first hospitalization for stroke were obtained from the Hospital Discharge Register during the study period 1987 to 2001. All individuals born in Sweden from 1932 onwards were included and linked to their siblings. Risks were calculated as standardized incidence ratios and compared with individuals without affected siblings. Results were standardized for age, gender, geographical region and socioeconomic status.

Results--Ischemic stroke (n=25 630) was associated only with ischemic stroke (n=7961), which was also the case for hemorrhagic stroke. The statistically significant standardized incidence ratios were 2.14 (95% CI, 1.21 to 3.74) and 1.82 (95% CI, 1.21 to 2.75), respectively. For discordant subtypes of stroke no significant associations were found.

Conclusions--The results suggest that ischemic and hemorrhagic stroke are not under the same genetic influence. However, further studies of the human genome are needed in order to identify the specific genes that play roles in the pathogenesis of common subtypes of stroke.