Joubert Syndrome 21

Alternative Names

  • JBTS21
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WHO-ICD-10 version:2010

Congenital malformations, deformations and chromosomal abnormalities

Congenital malformations of the nervous system

OMIM Number

615636

Mode of Inheritance

Autosomal recessive

Gene Map Locus

8q13.1-q13.2

Description

Ciliopathies are a group of phenotypically diverse disorders caused by primary cilium defects.  As the primary cilium is ubiquitous in mammalian tissues, ciliopathies have wide-ranging, multisystem effects.  Joubert syndrome is one such disorder.  It is characterized by brain anomalies such as cerebellar vermian hypoplasia/aplasia, thickened and reoriented superior cerebellar peduncles, and an abnormally large interpeduncular fossa.  These findings give the appearance of a molar tooth sign on a brain MRI.  Symptoms of the disorder include cerebellar ataxia, oculomotor apraxia, hypotonia, breathing difficulties, abnormal eye and tongue movements and intellectual disability.  Other symptoms that may be associated with the disorder include retinal dystrophy, renal disease, liver fibrosis and polydactyly of the hands and feet.  The congenital syndrome affects infants and is usually diagnosed right after birth.

Treatment of the disorder depends on the severity of symptoms.  It is focused mainly on physical, occupational and speech therapy as well as infant stimulation. 

Molecular Genetics

JBTS21 follows an autosomal recessive pattern of inheritance and hence is caused by homozygous or compound heterozygous mutations.  Around ten different genes have been linked to Joubert syndrome.  However, JBTS21 is caused specifically by mutations in the CSPP1 gene.  Most commonly, mutations result in amino acid substitutions or frameshift and terminations.

Epidemiology in the Arab World

View Map
Subject IDCountrySexFamily HistoryParental ConsanguinityHPO TermsVariantZygosityMode of InheritanceReferenceRemarks
615636.1United Arab EmiratesFemaleYesYes Seizure; Global developmental delay; Hyd...NM_024790.6:c.2131_2132delHomozygousAutosomal, RecessiveSaleh et al. 2021 Mother had recurrent...

Other Reports

Saudi Arabia

Shaheen et al. (2014) described a consanguineous Saudi family affected with ciliopathy.  The first child in this family was stillborn at 26 weeks.  The fetus suffered from hydranencephaly, occipital encephalocele, hyperechogenic kidneys and a single nostril.  While the second pregnancy resulted in a spontaneous first-trimester abortion, the third pregnancy resulted in a stillborn at 18 weeks.  This fetus showed similar findings of occipital encephalocele, hyperechogenic kidneys and a single nostril.  In addition, she had partially fused eyes. The symptoms in this family were found to be similar to Meckel-Gruber syndrome.  Genetic analysis revealed a homozygous frameshift deletion in the CSPP1 gene in affected members.  It was also predicted to cause premature truncation (p.Glu750Lysfs*7).  .  A skin biopsy from the first child revealed decreased numbers of ciliated fibroblasts and a complete loss of ciliary localisation of RPGRIP1L.  

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