Missing = disappearing and leaving no trace?

Context:

The vesicles are reused several times. This results in the gradual degradation of the proteins they need for carrying out their function properly, which in turn affects the release of signaling substances. How the vesicles are kept operational during this recycling process was a mystery until now. Most types of cells have incorporated an extra step into this recycling process via special cell compartments called endosomes. In the endosomes, vesicle proteins are sorted to ensure optimal functioning of the recycled vesicles.

However, it was not clear whether this extra step was relevant for vesicle recycling in brain cells. Various studies seemed to demonstrate that it was in fact missing in brain cells.

More:
http://www.sciencedaily.com/releases/2011/04/110401111356.htm