Joubert Syndrome 24

Alternative Names

  • JBTS24
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WHO-ICD-10 version:2010

Congenital malformations, deformations and chromosomal abnormalities

Other congenital malformations

OMIM Number

616654

Mode of Inheritance

Autosomal recessive

Gene Map Locus

12q24.31

Description

Joubert syndrome is a phenotypically heterogeneous ciliopathy classically defined by the presence of a ‘molar tooth sign’ in neurological imaging studies caused by brain anomalies such as cerebellar vermian hypoplasia/aplasia.  JBTS24 also results in polymicrogyria and pachygyria.  Neurological issues such as delayed psychomotor development, absent speech, ataxia, spasticity, hyperreflexia, dysmetria, hypotonia and impaired gait are common.  Other symptoms include postaxial polydactyly of the hands and feet and ophthalmological defects such as nystagmus and hyperopia.

Joubert syndrome has a prevalence of 1/80,000 to 1/100,000 live births and does not appear to have a gender or racial bias.  The congenital disorder has an onset in infancy and diagnosis can be made based on clinical features and radiological investigations.  Prognosis depends on the severity of symptoms.  While some children may have mild forms of the disorder, others suffer from severe motor disability and multi-organ defects.  Treatment is currently symptomatic and supportive.  Patients may benefit from physical, occupational and speech therapy.

Molecular Genetics

The disorder follows an autosomal recessive pattern of inheritance and is caused by homozygous mutations in the TCTN2 gene.  This gene encodes a protein of the tectonic family predicted to play a role in ciliogenesis and Hedgehog signaling.  TCTN2 mutations associated with JBTS24 include transitions and insertions that can result in exon skipping and premature termination.

Epidemiology in the Arab World

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Other Reports

Saudi Arabia

Al-Hamed et al. (2016) investigated a cohort of 44 Saudi families affected by antenatal cystic kidney disease, echogenic kidneys or enlarged kidneys and aimed to identify the causal gene defects.  In one family, antenatal ultrasound examination revealed cystic kidneys.  The case resulted in fetal death and DNA was unavailable for analysis.  However, the consanguineous parents were both found to be heterozygous for a novel TCTN2 mutation, c.252_253delTG (p.V85Dfs*24).  The frameshift mutation was predicted by ‘Mutation Taster’ to be disease causing.  

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