Joubert’s syndrome is a rare neurological disease that causes malformations in several brain structures, such as the cerebellum, and leads to respiratory, muscular and motor coordination problems in the person who suffers it.
In this article we explain what Joubert’s syndrome is, what its symptoms are and what causes it, and also how to diagnose and treat this disease.
What is Joubert’s syndrome?
Joubert’s syndrome is a rare congenital neurological disease characterized by malformation of the midbrain and cerebellum, specifically with a variable degree of dysgenesis of the cerebellar vermis, either by agenesis (defective development) or hypoplasia (incomplete development).
This syndrome was first described in 1969 and is named after Marie Joubert , a neurologist and pediatrician who researched the disease in Quebec, Canada.
The disease is an autosomal recessive condition (two copies of the abnormal gene must be present for the disease to develop) and is clinically heterogeneous, as some patients may have other disorders such as Leber’s congenital amaurosis (disease of the retina), nephronoptisis (diseases affecting the kidney), and/or cystic medullary kidney disease.
It is estimated that this syndrome can affect 1 in 80,000 or 100,000 newborns . However, this estimate seems to be too low, as this syndrome has a wide range of characteristics and clinical signs, so it may not be diagnosed sufficiently.
On the other hand, the genetic mutations that cause this condition are more common in certain ethnic groups, such as Ashkenazi Jews, French Canadians, and Hutterites.
Clinical signs and symptoms
One of the distinguishing features of Joubert’s syndrome is what is known as the “molar tooth sign”, which is detectable in neuroimaging studies, such as in magnetic resonance imaging: the upper cerebellar peduncles, enlarged in size and in a horizontal position, together with the elongated bridge-mesencephalon junction, produce this molar tooth or molar tooth image.
During the course of the neonatal period, Joubert’s syndrome is often manifested by irregular breathing (episodic tachypnea and/or apnea) and nystagmus. Later, in childhood, hypotonia (decreased muscle tone) may occur and later, the patient may develop cerebellar ataxia (unsteady gait and imbalance).
Delayed motor development is also common. The intellectual faculties of people suffering from this rare disease can vary from severe intellectual deficit to normal or standard intelligence. Occasionally, neuro-ophthalmological examination may detect the presence of oculomotor apraxia.
These patients usually present a characteristic face: large head, prominent forehead, high and rounded eyebrows , epicanthal folds, ptosis, upturned nose, open mouth, rhythmic tongue protrusion movements (spontaneous sticking out of the tongue) and sometimes low set ears.
Other clinical manifestations present in Joubert’s syndrome involve retinal dystrophy, polydactyly, and seizures (more rare).
Joubert’s syndrome can be caused by mutations in more than 30 different genes . Studies suggest that the proteins produced from these genes would play an important role in the cellular structures called primary cilia. The cilia are microscopic villi of the cerebellar vermis which protrude from the surface of the cells and are involved in the detection of the physical environment and chemical signalling.
The alterations of this disease would come from the absence or low degree of development of the middle part of the cerebellum, the vermis, and the cilia located in the plasma membrane of the cells of this structure of the brain, which move the cerebrospinal fluid.
Primary cilia are important for the structure and function of many types of cells, including neurons and certain cells of the kidneys and liver. These tiny villi are also necessary for the perception of sensory information, which the brain interprets for the senses of sight, hearing, and smell.
However, the genetic mutations known to be associated with Joubert’s syndrome would account for 60-90% of all cases of this disease. In the remaining cases, the specific cause is not yet known.
The diagnosis of Joubert’s syndrome is based on clinical and radiological data . We have already reviewed the clinical signs and symptoms, and with regard to the radiological classification of the syndrome, it could be divided into: mild, moderate and severe vermis dysgenesis.
Some researchers have also suggested the existence of two other groups: one that has additional abnormalities of the brain, cerebellum (excluding vermis) or brain stem; and another, in which the radiological features of the syndrome are absent.
Nuclear magnetic resonance imaging shows partial or complete absence of cerebellar vermis, normal or decreased posterior fossa, and an absence of pyramidal decustation (crossing of pyramidal fibers, which travel from the cortex to the spinal cord).
Patients diagnosed with Joubert’s syndrome also present lengthening and narrowing of the junction between the bridge and the midbrain, a deep interpeduncular fossa with thickening of the upper cerebellar peduncles and hypoplasia and incomplete fusion of the mid-vermis region.
In some cases, the so-called sign of the molar tooth, which we have discussed above, is for some professionals a pathognomonic sign of the syndrome; that is, a clinical manifestation that is only found in a certain morbid state and that is sufficient in itself to characterize the disease and to establish the diagnosis.
There is no specific cure or treatment for Joubert’s syndrome . The usual approach is to treat the symptoms and underlying conditions of the disease. The management of this disorder requires a multidisciplinary approach, with special attention to respiratory and feeding problems in neonates and children, sometimes requiring monitoring of respiratory function.
Pharmacological intervention is usually required to attenuate the most disabling physical symptoms, as well as early stimulation, both physically and cognitively. A neuropsychological, cognitive and behavioural evaluation is also recommended, with the aim of providing younger patients with the necessary tools to carry out a comprehensive rehabilitation.
On the other hand, identifying and controlling aspects inherent to the disease itself, such as eye degeneration, kidney complications and other disorders associated with the syndrome, should be a priority and should be done as soon as possible, in order to adjust therapeutic measures to the specific needs of the patient.
Angemi, J., & Zuccotti, J. (2012). Updates on Joubert’s Syndrome. ALCMEON.
Bibas, H., Colonel, A. M., Fauze, R., & Sialle, M. (2005). Joubert’s syndrome and “molar sign” in the cerebello-occulo-renal malformative complex in two patients. Chilean Journal of Pediatrics, 76(6), 605-611.
Yachnis, A. T., & Rorke, L. B. (1999). Neuropathology of Joubert syndrome. Journal of child neurology, 14(10), 655-659.