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Joubert syndrome
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Joubert syndrome

Joubert syndrome is a brain development disorder characterized by a specific brain abnormality known as the "molar tooth sign" and a wide range of physical and neurological symptoms.

Overview

Joubert syndrome affects the development of the cerebellum and brainstem. The hallmark feature is the "molar tooth sign," visible on MRI scans, which occurs due to the abnormal development of these brain structures.

Symptoms

  • Neurological: Low muscle tone (hypotonia), breathing irregularities (episodes of fast or slow breathing), abnormal eye movements, and ataxia (problems with balance and coordination).
  • Developmental: Intellectual disabilities ranging from mild to severe, and delays in speech and motor skills.
  • Additional features: Seizures, behavioral problems, kidney disease, liver disease, skeletal abnormalities (such as extra fingers or toes), and retinal dystrophy causing vision loss.

Causes

Joubert syndrome is caused by variants in one of more than 40 genes. Most of these genes are involved in the structure and function of primary cilia—microscopic, finger-like projections on the surface of cells that act as sensory antennae. Defective cilia disrupt signaling pathways necessary for early development.

Inheritance

Inheritance patterns vary based on the specific genetic cause:

  • Autosomal recessive: The most common pattern, requiring two copies of the altered gene.
  • Autosomal dominant: A rarer pattern where one copy of the altered gene is sufficient.
  • X-linked: A rare pattern where the gene is located on the X chromosome, affecting males more frequently.

Frequently Asked Questions

Most cases are autosomal recessive, giving a 25% recurrence risk for each subsequent pregnancy. Targeted carrier testing of both parents for the identified pathogenic variant confirms carrier status. If the variant is known, pre‑implantation genetic testing (PGT‑M) or prenatal diagnostic testing (chorionic villus sampling or amniocentesis) can be offered.
Infants often present with hypotonia, irregular breathing patterns (periods of rapid or shallow breathing alternating with pauses), and abnormal eye movements such as nystagmus or oculomotor apraxia. When these neurologic signs are combined with developmental delay, especially in the first year of life, a brain MRI is warranted to look for the characteristic “molar tooth sign.”
Because up to 30% of patients develop nephronophthisis or hepatic fibrosis, guidelines advise baseline renal ultrasound and liver function tests (ALT, AST, GGT, bilirubin) at diagnosis, then repeat every 6–12 months. Urinalysis for proteinuria and serum creatinine are also monitored annually. Early detection allows timely referral to nephrology or hepatology.
Most breathing episodes are self‑limited and improve with age, but severe apneas may require monitoring in a sleep‑study unit. Supplemental oxygen is rarely needed; instead, caregivers are taught to position the infant supine, avoid over‑sedation, and use pulse‑oximetry at night if apnea is frequent. In rare cases, a home apnea monitor is prescribed.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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