What to Know About Joubert Syndrome
This article discusses Joubert syndrome, including its causes, symptoms, treatments, and outlook.
Joubert syndrome is caused by genetic mutations that influence the production of certain proteins in the body. These proteins, in turn, affect the development of structures called primary cilia.
Primary cilia are small structures that protrude from the surface of cells. They play a role in many functions, including:
- chemical signaling
- sensory input, which affects hearing, sight, and smell
- brain, kidney, and liver cell function
It is thought that primary cilia dysfunction is the cause of the clinical features of Joubert syndrome. However, the exact way they influence a fetus’s development is not well understood.
Joubert syndrome results in an atypical brain stem and an underdeveloped or absent cerebellum. The cerebellum is the part of the brain responsible for coordination and balance.
More than 30 genes have been identified as contributing to the development of Joubert syndrome. Some of the most commonly involved genes include:
Joubert syndrome can be passed down from parents to their children. It is an autosomal recessive disorder. This means a child must receive a copy of a mutated gene from both parents in order to develop the condition.
Joubert syndrome can also develop spontaneously, meaning it occurs without a known genetic cause.
Features and conditions that may indicate Joubert syndrome often include:
- hypotonia, or decreased muscle tone
- ataxia, or poor muscle control
- developmental delays
- intellectual disabilities
- hyperpnea, or rapid breathing
- sleep apnea
- atypical tongue or eye movements
People with the condition may also experience seizures, physical irregularities such as a cleft palate, or kidney and liver dysfunction.
These signs are usually apparent in infancy and can range from mild to severe. Their severity can depend on the extent to which the brain is affected and which other organs are involved.
Joubert syndrome can be divided into subtypes based on the specific signs that are present. JS-ret is a subtype that refers to Joubert syndrome with retinal disease. It causes the eye’s retina to degenerate. Another subtype is JS-ren. This refers to Joubert syndrome with renal disease, which affects the kidneys.
To diagnose Joubert syndrome, doctors will perform a comprehensive physical examination and neurologic assessment. Diagnosis will also typically involve a brain MRI scan.
To confirm a diagnosis, doctors look for three main clinical signs:
- hypotonia, or decreased muscle tone
- intellectual disabilities or developmental delays
- molar tooth sign, a characteristic brain abnormality
Cerebellar vermis hypoplasia and the molar tooth sign
The cerebellum is the part of the brain that controls movement. The vermis is a structure that separates the cerebellum into two hemispheres.
When the vermis is underdeveloped or smaller than usual, this is referred to as cerebellar vermis hypoplasia. This and other brainstem irregularities can resemble the cross-section of a molar tooth when viewed on an MRI scan.
In about 60–90% of Joubert syndrome cases, molecular genetic testing can allow doctors to determine which gene is involved.
Additional tests may be necessary to evaluate the function of other organ systems such as the eyes, kidneys, and liver.
Treatment for Joubert syndrome focuses on relieving symptoms and providing mental and physical support. This may involve:
- physical or occupational therapy
- speech therapy
- supplemental oxygen or mechanical ventilation for infants and children with breathing difficulties
- educational support
- surgery for physical irregularities
- dialysis or kidney transplantation
- corrective lenses for eye symptoms
People with Joubert syndrome may have shorter life expectancies than those without the condition.
In a 2017 study, researchers looked at 40 cases of Joubert syndrome. They found the average life expectancy to be 7.2 years. Respiratory and kidney failure were the main causes of death.
Researchers in this study also noted that little is known about the condition and its mortality rates. Because of this, more studies are needed to determine how Joubert syndrome affects life expectancy.
Joubert syndrome can cause progressive complications affecting the eyes, liver, and kidneys. For this reason, doctors typically recommend routine screenings.
William C. Lloyd III, M.D., reviewed the answers to these common questions about Joubert syndrome.
Can Joubert syndrome be cured?
There is currently no cure for Joubert syndrome. Treatment focuses on symptom management and therapies to provide physical and mental support. Researchers are continuing to study the condition in order to find more effective treatments.
Can you live a full life with Joubert syndrome?
Life expectancy for someone with Joubert syndrome can depend on the severity of symptoms. A person experiencing severe respiratory difficulties or kidney dysfunction may not live as long as someone with milder symptoms.
Can you detect Joubert syndrome before birth?
If a parent is a known carrier of a genetic mutation involved in the development of Joubert syndrome, genetic testing may lead to a prenatal diagnosis.
Joubert syndrome is a rare disorder that affects the development of a fetus. It can cause signs such as ataxia, atypical breathing patterns, and irregular eye movements.
Doctors can confirm a diagnosis by evaluating physical and neurological findings along with brain MRI features. Treatment focuses on symptom management and regular screenings for additional complications.
Talk with your doctor about ways to manage Joubert syndrome.