Moyamoya disease is a progressive cerebrovascular occlusive disease that occurs 
frequently in children. The etiology is unknown. We examined changes in 
biological characteristics and responsiveness to serum mitogens during the in 
vitro cellular aging of arterial smooth muscle cell strains derived from 
patients with moyamoya disease (HMSMC) and compared them with those of cells 
from age-matched control patients (HCSMC). HMSMC had a normal human diploid 
chromosome constitution. HMSMC and HCSMC had almost the same in vitro life span 
and the age-related patterns of biological parameters were essentially the same. 
However, the doubling time at the early passages was significantly longer in 
moyamoya SMC than control SMC, although there was no significant difference at 
the late passages. Furthermore, the poor responsiveness of moyamoya SMC to 
platelet-derived growth factor was retained throughout the life span in vitro. 
These results support the hypothesis that functional alterations in vascular 
cells are involved in the mechanism of development of intimal thickening in 
moyamoya disease.