Joubert syndrome and related disorders.

The cerebellum plays a role not only in motor control but also in motor learning and cognition. Joubert syndrome is a rare heterogeneous inherited genetic disorder characterized by ataxia, hypotonia, developmental delay, and at least one of the following features: neonatal respiratory disturbances or abnormal eye movement. The estimated frequency of Joubert syndrome in the United States is around 1 : 100 000. The term Joubert syndrome and related disorders (JSRD) has been recently coined to describe all disorders presenting with molar tooth sign on brain neuroimaging. Joubert syndrome is believed to be a representative of a new group of disorders named ciliopathies. The identification of seven causal genes (NPHP1, AHI1, CEP290, RPGRIP1L, TMEM67/MKS3, ARL13B, CC2D2A) has led to substantial progress in the understanding of the genetic basis of Joubert syndrome. The authors focus on clinical presentation of JSRD, differential diagnosis and molecular background.