Joubert syndrome (JBTS) is an autosomal recessive condition characterized by congenital malformations of the brain stem and agenesis/hypoplasia of the cerebellar vermis (shown as a "molar tooth sign" in magnetic resonance imaging). Common symptoms in the neonatal period are tachypnea/dyspnea, nystagmus, vertical gaze palsy and muscular hypotonia. Later, cerebellar ataxia with delayed motor development can be observed. The cognitive development of patients can range from normal intelligence to severe deficits. In some cases JBTS may be associated with nephronophthisis, optic nerve coloboma, liver fibrosis and polydactyly. The frequency of occurrence of JBTS is estimated to be approximately 1:100,000.
JBTS has a large gene locus heterogeneity. Pathogenic variants in multiple genes have been identified, so a mutation analysis is extensive. However, a genetic cause is only detected in 40 to 50% of cases of JBTS. Similar to nephronophthisis, JBTS is counted among the so-called ciliopathies.
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