What Is Joubert Syndrome 2 (JBTS2)?

JBTS2 is an inherited condition caused by mutations in the TMEM216 gene that lead to abnormalities in the brain structure. Symptoms include developmental delay, the inability to coordinate muscle movement, involuntary eye movements, and difficulty moving the eyes from side to side. Individuals may also exhibit intellectual disability.

At birth, children with JBTS2 have poor muscle tone. Their eyes move rapidly and involuntarily and may rotate inward. They often have difficulty eating due to problems coordinating their muscle movement, and they may have breathing problems due to structural brain abnormalities. Some children with JBTS2 have additional fingers and/or toes (polydactyly). In addition, some children with JBTS2 will have kidney problems, which may lead to kidney failure in adolescence.

Children with JBTS2 all have delayed mental and physical development. They may have mild to severe intellectual disability, though a few individuals have attended college. In the first few years of life, their eye problems often improve, leading to normal vision.

How Common Is JBTS2?

The worldwide incidence of JBTS2 is unknown. JBTS2 is common in Ashkenazi Jews, of whom 1 in 34,000 is affected.

How Is JBTS2 Treated?

There is no cure for JBTS2. A medical team can address symptoms as they arise. Regular examinations are necessary since symptoms may vary. Infants with difficulty eating should be monitored to ensure that they are receiving proper nutrition. Physical and occupational therapy may also be helpful. Children with JBTS2 should also be monitored for eye and kidney problems.

What Is the Prognosis for a Person with JBTS2?

The prognosis for a person with JBTS2 varies. Some will have milder forms of intellectual disability and mild ataxia (lack of muscle control), while others will have more severe intellectual disability and movement problems. A minority of individuals will have a shorter lifespan due to kidney or liver failure and breathing abnormalities.

Other names for
Joubert syndrome 2

  • CORS2
  • Cerebellooculorenal syndrome 2
  • JBTS2


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  • OMIM: Online Mendelian Inheritance in Man, OMIM [608091], 2016, http://www.omim.org/608091
  • Parisi et al., 2017, https://www.ncbi.nlm.nih.gov/books/NBK1325/
  • Valente et al., 2010, Nat Genet, 42(7):619-25, PMID: 20512146