EFNB1 and obesity due to melanocortin 4 receptor deficiency: However, obesity-induced inflammation results in ephrin-B1 downregulation at the top of the crypt, disrupting the repulsive EphB2/ephrin-B1 interaction and promoting the migration of mutation-harbouring cells at the bottom of the crypt; cells in the crypt evade apoptosis and eventually grow into adenoma.