The molar tooth sign is a frequent and reliable sign of JS and related disorders.Genes related to defective cilia result in malfunctioning in the retina, renal tubule, and neural cell migration thus producing heterogeneous syndrome complexes known as “ciliopathies.” Other ciliopathies like Senior-Loken syndrome, Bardet Biedl syndrome, and isolated nephronophthisis must be considered as the differential diagnosis of JS.The main imaging findings are the partial or complete absence of the cerebellar vermis, hypoplastic cerebellar peduncles (giving MTS), and (bat-wing appearance) fourth ventricular deformity.
Traditionally, all patients with the molar tooth sign on axial imaging were given the diagnosis of Joubert syndrome. In recent years, wide clinical variation in patients with the molar tooth sign has become apparent and these disorders are classified as part of the larger cerebellooculo-renal syndromes (CORS).
Related disorders such as Dekaban-Arima syndrome, COACH syndrome, and Senior-Loken syndrome may also demonstrate the molar tooth sign, and they often share the clinical syndrome related to hindbrain malformation with Joubert patients.
Sometimes patients have abnormal eye movements with oculomotor apraxia. Approximately 10% of patients with Joubert syndrome are initially misdiagnosed with a Dandy-Walker variant.
JS mostly occurs in male children. Hypotonia and ataxia are the most common characteristic signs of JS, and most children with JS have cognitive dysfunction. Other findings of JS include cystic kidney disease, retinal dystrophy, hepatic fibrosis, and polydactyly, colobomas.
In 2017, Vilboux et al. claimed that there were more than 30 genes (NPHP1, OFD1, TCTN2, TCTN3, TMEM138, TMEM216, TMEM231, and so on) associated with JS. Till now, more than 35 genes have been confirmed to be the cause of JS by mutating in an autosomal-recessive or X-linked manner. This suggests that there are more and more causative genes that need to be identified by innovative technologies. The rapid rate of genetic discoveries plays an important role in addressing the issue of genetic counseling