Joubert syndrome with renal defect

Joubert syndrome with renal defect (also known as Joubert syndrome type B or cerebello-oculo-renal syndrome when ocular features are present) is a rare genetic disorder characterized by the hallmark brain malformation known as the 'molar tooth sign' on brain MRI, combined with kidney (renal) abnormalities. The molar tooth sign results from cerebellar vermis hypoplasia and abnormal configuration of the superior cerebellar peduncles. This condition belongs to the broader group of Joubert syndrome and related disorders (JSRD), which are classified as ciliopathies — diseases caused by dysfunction of primary cilia, cellular structures critical for signaling during development. The neurological features of Joubert syndrome with renal defect include hypotonia (low muscle tone) in infancy, developmental delay, intellectual disability of variable severity, abnormal breathing patterns (episodic hyperpnea/apnea) in the neonatal period, and ataxia (impaired coordination). The renal involvement can include nephronophthisis (a progressive tubulointerstitial nephropathy that may lead to end-stage renal disease), cystic kidney dysplasia, or other structural kidney anomalies. Renal disease may be present from birth or develop progressively during childhood, and regular monitoring of kidney function is essential for early detection and management. There is currently no cure for Joubert syndrome with renal defect. Treatment is supportive and multidisciplinary, focusing on developmental therapies (physical, occupational, and speech therapy), management of breathing abnormalities, and close monitoring and treatment of renal complications, which may ultimately require dialysis or kidney transplantation if end-stage renal disease develops. Multiple genes have been implicated in this condition, including CC2D2A, TMEM216, RPGRIP1L, CEP290, NPHP1, and others, all encoding proteins involved in ciliary function. Genetic testing is important for confirming the diagnosis, guiding surveillance, and providing accurate genetic counseling for affected families.

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