Joubert syndrome (JBTS) is a heterogeneous disorder characterized by neurodevelopmental delay, hypoplasia of the cerebellar vermis with a specific sign of molar tooth in midbrain, hypotonia and abnormal eye movements. Associated clinical features of JBTS can be polycystic kidney disease, polymicrogyria, polydactyly, occipital encephalocele and liver fibrosis. The incidence of JBTS in the USA is 1 in 80,000–100,000 individuals.
Clinical features of Joubert syndrome type 9 (JBTS9; OMIM 612285) present ventriculomegaly and the molar tooth sign on magnetic resonance imaging (MRI) of the brain. Genetic analysis of JBTS9 has been associated with alterations in coiled-coil and C2 domain-containing protein 2A gene (CC2D2A; OMIM 612013), which was identified for the first time in a Pakistani family from a Punjabi ethnic group. The patients were characterized by intellectual disability with retinitis pigmentosa and the causative gene (CC2D2A) was identified through genomewide linkage analysis followed by Sanger sequencing.