Fact-sheet: Joubert syndrome


Updated on 11/28/2024 at 10:24 AM

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Definition

Joubert syndrome is a rare multiple malformation syndrome characterized by cerebellar vermis hypoplasia and dysplasia, associated with brainstem abnormalities. It is inherited in an autosomal recessive manner with a recurrence rate of 25%.

Joubert syndrome is the most common rhombencephalosynapsis.

Prevalence: 1 in 100,000 children

Clinical features

Neonatal period: irregular breathing and nystagmus

Childhood: cerebellar ataxia, developmental delay, variable intellectual capacity, oculomotor apraxia, seizures

Facial features: macrocephaly, prominent forehead, high-arched eyebrows, epicanthus, upturned nose, open mouth

Associated abnormalities:

  • Retinal involvement (Leber congenital amaurosis)
  • Renal involvement (Dekaban-Arima)
  • Ocular and hepatic involvement (COACH)
  • Juvenile forms (Senior-Löken)

Laboratory findings

Molecular genetic analysis is not essential for initial diagnosis, which is based on clinical findings and MRI

Ultrasound

Associated malformations:

  • Renal cysts
  • Hepatic fibrosis and cysts

Renal and hepatic ultrasound workup at diagnosis

The diagnosis of certain brain malformations, including polymicrogyria, can be difficult to establish in utero by ultrasound, owing to the anatomy of the fetal brain

MRI

Reference examination

  • Vermian hypoplasia or agenesis associated with an interhemispheric cleft
  • "Molar tooth sign": The superior cerebellar peduncles are stretched horizontally, giving the brainstem and upper part of the fourth ventricle a characteristic molar tooth appearance on axial images. This sign is visible on T1 and T2 sequences in 85% of cases. It results from thinning of the midbrain, horizontalization and thickening of the superior cerebellar peduncles, and vermian hypoplasia. This sign is not entirely specific.
  • Fusion of the two cerebellar hemispheres
  • Midbrain hypoplasia
  • Widening of the interpeduncular fossa
  • Umbrella-shaped dilatation of the fourth ventricle
  • Absence of decussation of the superior cerebellar peduncles and corticospinal tracts: This anomaly is not visible on MRI with standard sequences but can be demonstrated with diffusion tensor imaging.
  • Gray matter heterotopia in the interpeduncular fossa

Management

No curative treatment

Symptomatic treatment

Psychomotor rehabilitation

Ophthalmologic, nephrologic, and hepatologic monitoring as needed

Multidisciplinary follow-up

Differential diagnosis

Other syndromes presenting with abnormalities of the cerebellar vermis and brainstem, such as:

  • Vermian agenesis: Rhombencephalosynapsis
  • Dandy-Walker syndrome
  • Other malformation syndromes with the "molar tooth sign", pontocerebellar hypoplasia

Careful analysis of MRI findings, particularly the appearance of the vermis, superior cerebellar peduncles, and pontomesencephalic junction, allows differentiation of these entities.