Joubert syndrome

Joubert syndrome is a genetic birth defect. The cerebellum of people with the disorders is not developed normally. The disorder does not occur very often. Since its first description in 1969, a few hundred cases have been described. It is a ciliopathy. 
Mutations at 21 different loci have been found to cause Joubert syndrome. 
Ciliopathy.
Research has shown that a number of genetic disorders may be related as to their root cause. Joubert syndrome is one such disease. It is a member of a class of diseases called ciliopathies.
The underlying cause of the ciliopathies may be defects in the mechanism of cilia in the cell. Cilia are organelles which are present in many cell types in the body. The cilia defects damage "critical developmental signaling pathways" essential to cell development. This explains the multi-symptom nature of many syndromes and diseases.
Currently about nine ciliopathies are known, including Joubert syndrome.