Joubert syndrome is a rare genetic disorder characterized by decreased muscle tone, difficulties with coordination, abnormal eye movements, abnormal breathing patterns and intellectual disability. These issues are due to abnormal brain development, resulting in decreased size of the cerebellar vermis and other brain abnormalities that appear as the “molar tooth sign” on a brain MRI. (Upper Left) Although rare, several hundred individuals with Joubert syndrome have been reported in the medical literature. Mutations in at least 22 genes cause Joubert syndrome, accounting for ~60% of patients. Subsets of individuals with Joubert syndrome can also have polydactyly (extra fingers or toes), as well as retinal, kidney and liver disease requiring medical intervention.

Joubert syndrome is one of a growing group of disorders called “ciliopathies” caused by dysfunction of a part of the cell called the cilium (Lower Right). The cilium functions as an antenna for many cell types, allowing cells to communicate with each other and sense their environment during the development and function of many organs. In fact, cilia are required to sense light in the eye, odors in the nose and fluid flow in the kidneys and liver. Disruption of cilium function likely explains the incidence of eye, kidney and liver problems in individuals with Joubert syndrome.