Then, Olsen and some colleagues became interested in how blood vessels form and what determines vascular patterns in a developing organism. Olsen and Mulliken wanted to learn how the different cell types in blood vessels communicate. To answer these questions, they started looking at specific genes that express themselves in abnormal vessels. The endothelium form a single layer of cells lining a vein, representing a barrier to the blood. Outside of these cells, in the blood vessel wall itself, are smooth muscle cells.
Arteries have many layers of smooth muscle cells, and the veins have few layers of muscle cells.
About the time Olsen and Mulliken were beginning to investigate these questions, a surgeon from Belgium, Laurence Boon, came to study plastic surgery under Mulliken. Boon also wanted to do some research, so Mulliken arranged for her to work in Olsen's laboratory on a project related to venous malformations. Mulliken knew about a family that had an inherited form of venous malformations, and he and Olsen wanted to find the gene that triggers the abnormalities. Current methods of treating the large, jumbled masses of abnormal veins by operations or injections do not always produce lasting results. At the same time, another postdoctoral researcher who had experience mapping genes, Miikka Vikkula, arrived from Finland to work in Olsen's lab.