Joubert syndrome type 4 (JBTS4) is an autosomal recessive disorder presenting with cerebellar ataxia, oculomotor apraxia, hypotonia, neonatal breathing abnormalities and psychomotor delay. Neuroradiologically, it is characterized by cerebellar vermian hypoplasia/aplasia, thickened and reoriented superior cerebellar peduncles, and an abnormally large interpeduncular fossa, giving the appearance of a molar tooth on transaxial slices (molar tooth sign). Additional variable features include retinal dystrophy and renal disease. JBTS4 is a phenotypically mild form.
Among a cohort of 20 children from 17 independent Egyptian families, who met the clinical and ultrasonographic criteria of nephronophthisis, Soliman et al. (2010) found four patients with molar tooth sign on brain MRI, ataxia, mental retardation, retinal dystrophy, oculomotor apraxia, and facial dysmorphy, and hence were clinically categorized as having a Joubert syndrome-related disorder (JSRD). One of these patients was found to have homozygous deletion in the NPHP1 gene.