Color-enhanced scanning electron micrograph of red blood cells leaking out of a ruptured blood vessel. This is due to a mutation in the ephrin-B2 gene that causes the blood vessels to be more fragile than normal leading to an increased rate of haemorrhaging. The fragility is due to the inadequate coverage of the vessel by smooth muscle cells. This kind of leaky blood vessel is frequently found in tumours and in certain other human diseases.