Question: What is (are) Joubert syndrome ?
Answer: Joubert syndrome is disorder of abnormal brain development that may affect many parts of the body. It is characterized by the absence or underdevelopment of the cerebellar vermis (a part of the brain that controls balance and coordination) and a malformed brain stem (connection between the brain and spinal cord). This gives a characteristic appearance of a molar tooth sign on MRI. Signs and symptoms can vary but commonly include weak muscle tone (hypotonia); abnormal breathing patterns; abnormal eye movements; ataxia; distinctive facial features; and intellectual disability. Various other abnormalities may also be present. Joubert syndrome may be caused by mutations in any of many genes and is predominantly inherited in an autosomal recessive manner. Rarely it may be inherited in an X-linked recessive manner. Treatment is supportive and depends on the symptoms in each person.
Source: GARD

Question: What causes Joubert syndrome ?
Answer: What causes Joubert syndrome? Joubert syndrome and related disorders may be caused by changes (mutations) in any of many genes (some of which are unknown). The proteins made from these genes are either known, or thought, to affect cell structures called cilia. Cilia are projections on the cell surface that play a role in signaling. They are important for many cell types, including neurons, liver cells and kidney cells. Cilia also play a role in the senses such as sight, hearing, and smell. Mutations in the genes responsible for Joubert syndrome and related disorders cause problems with the structure and function of cilia, likely disrupting important signaling pathways during development. However, it is still unclear how specific developmental abnormalities result from these problems.
Source: GARD