Juvenile nephronophthisis on MRI—a potential case of Joubert syndrome?
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- Simms, R.J. & Sayer, J.A. Pediatr Radiol (2010) 40: 1581. doi:10.1007/s00247-010-1707-6
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Nephronophthisis accounts for 6.5% of the children requiring renal replacement therapy in the United Kingdom and may be underdiagnosed . As the authors acknowledge, an important feature of nephronophthisis is the association with extra-renal manifestations that can occur in up to 10% . In their discussion, the authors mention Joubert syndrome, which is characterized by a mid-hindbrain malformation, cerebellar vermis hypoplasia and the diagnostic “molar tooth sign” on cerebral MRI . We wonder whether the “abnormal gait” described in this child could be explained by Joubert syndrome and perhaps imaging with a brain MRI would be helpful?
The MRI of the kidneys clearly demonstrates the corticomedullary cysts characteristic of nephronophthisis/medullary cystic kidney disease . Diagnosis should be confirmed by molecular genetic analysis. In isolated nephronophthisis, mutations in NPHP1 account for 20–25% of cases and can be screened for by polymerase chain reaction (see http://www.orpha.net for a list of laboratories) . Additionally, retinal screening for retinal dystrophy is indicated in all cases of suspected nephronophthisis.
Since nephronophthisis is an autosomal-recessive condition, with little genotype-phenotype correlation, the importance of a family history and reviewing other potentially at-risk relatives should be emphasised.