It is noteworthy that although we observe a similar leaky blood vessel phenotype to that reported in tumour growth in pdgf-bret/ret mice, our results indicate that α6β1-integrin is a regulator of pericyte function rather than numbers, as opposed to the reduction in numbers seen in the pdgf-bret/ret mice (Lindblom et al., 2003). The gene discussed is RET; the disease is neoplasm.