Expression pattern of the Kallmann syndrome gene in the olfactory system suggests a role in neuronal targeting.

Kallmann syndrome is a genetic disorder characterized by a defect in olfactory system development, which appears to be due to an abnormality in the migration of olfactory axons and gonadotropin releasing hormone (Gn-RH) producing neurons. The X-linked Kallmann syndrome gene shares significant similarities with molecules involved in neural development. We have now isolated the evolutionarily conserved chicken homologue of the Kallmann gene. In the developing and adult chicken, high levels of expression were found in the mitral cells of the olfactory bulb (the target of olfactory axons) and in the Purkinje cells of the cerebellar cortex, both areas affected in patients with Kallmann syndrome. We propose a model in which the Kallmann syndrome gene product is a signal molecule required for neuronal targeting throughout life.