Joubert syndrome is a rare brain malformation characterized by the absence or underdevelopment of the cerebellar vermis, an area of the brain that controls balance and coordination. The most common features of Joubert syndrome in infants include abnormally rapid breathing (hyperpnea), decreased muscle tone (hypotonia), jerky eye movements (oculomotor apraxia), mental retardation, and the inability to coordinate voluntary muscle movements (ataxia). Physical deformities may be present, such as extra fingers and toes (polydactyly), cleft lip or palate, and tongue abnormalities. Kidney and liver abnormalities can develop, and seizures may also occur. Most cases of Joubert syndrome are sporadic (not inherited). In some families, however, Joubert syndrome appears to be inherited in an autosomal recessive manner (meaning both parents must have a copy of the mutation) via mutation in a number of genes, including NPHP1, AHI1, and CEP290.