Morphological and hemodynamic variations of the circle of Willis (CW) may have an
important impact on cerebrovascular events. However, the environmental and genetic
influence remains unclear. For this reason we studied the variations and hemodynamic
parameters of the CW in twins using transcranial color-coded sonography (TCCS). Sixty-four
twins, 19 monozygotic (MZ) and 13 dizygotic (DZ) pairs from the Italian Twin Registry
(average age 45.0 +/- 13.7 years) underwent TCCS and risk factor assessment. We examined
CW morphology and recorded peak systolic velocity (PSV), end-diastolic velocity (EDV)
and pulsatility index (PI). Raw heritability was determined for hemodynamic parameters,
whereas concordance and discordance rates were calculated for CW morphological variants.
A normal CW anatomy was observed in the majority of MZ and DZ twins (76.5% and 92.3%,
respectively). The most frequent variant was a missing anterior cerebral artery (ACA).
There was no significant difference in the prevalence of most CW variants depending
on the zigosity. Concordance rates were low regarding the presence of variant CW anatomy
both in MZ and DZ groups (0.14 and 0.00, respectively). Women had a significantly
higher PI in vertebral arteries (VA) and in the right ACA (p = 0.01, p = 0.02 and
p < 0.01, respectively). An inverse correlation was observed between hemodynamic parameters
and age. Morphological variants of the CW do not seem to be heritable; they are most
likely determined by environmental factors. In contrast, hemodynamic parameters of
the CW are moderately heritable and this might have implications in the management
and prevention of cerebrovascular diseases.
