Teaching Case

2-year-old male. First pregnancy of non-consanguineous parents, obtained at term by cesarean section due to cephalopelvic disproportion, without crying and cyanosis that required ventilatory support. Sucking with choking, poor support of the head. Epicanthus and anteverted nostrils, long philtrum, retrognathia, diastasis recti, limbs with diminished trophism and tone.

The brain MRI findings indicate hypoplasia of the cerebellar vermis, and the fourth ventricle appears somewhat reduced in size. The superior cerebellar peduncles show a prominent horizontalization, which gives a "molar tooth" appearance in the midbrain. Furthermore, the fourth ventricle appears compressed, giving it the typical look of a “bad wing”.

Joubert syndrome (JS) was first described by Joubert in an article that presented the clinical and radiological findings of a family with some affected members [1]. It is a rare disorder with a prevalence of 1:80,000–100,000 live births that causes neurodevelopmental abnormalities, along with other abnormalities depending on the mutation involved [2]. It has an autosomal recessive pattern of inheritance, and it is part of a group of diseases classified as congenital ciliopathies [3], which are a group of genetic disorders caused by abnormal formation or function of primary cellular cilia. To date, more than 35 causative genes have been identified, and only one of them is linked to the X chromosome; together, these genes represent 62–94% of cases [3].

Characterized by malformation of the cerebellum and brainstem, hypotonia, and developmental delay. Its earliest manifestation is the alteration of the respiratory pattern (tachypnea or neonatal episodic apnea), to which nystagmus and oculomotor apraxia are added. After a few months, hypotonia and cerebellar ataxia may appear, delaying neurological milestones, impairing cognitive abilities. Other anomalies described are nephronophthisis, liver fibrosis, retinal dystrophy, ocular colobomas, polydactyly, oral hamartomas, and endocrine disturbances [3]. Facial dysmorphisms such as prominent forehead, ptosis, prognathia, hypertelorism, tongue protrusion, and low-set ears have also been observed [4].

JS can be combined with a wide spectrum of organic defects, which is why it is known as "Joubert syndrome and associated disorders".

Diagnosis is based on clinical and radiological data. In some cases, a genetic mutation associated with the syndrome is detected [3]. The radiological manifestations usually present the classic “molar sign” due to the lack of decussation of the fibres of the superior cerebellar peduncle, which leads to their elongation and horizontalization in their course, together with an enlargement of the interpeduncular cistern [ 4]. Other features are hypo/aplasia of the cerebellar vermis and narrowing at the pontomesencephalic junction. Cortical dysplasias, polymicrogyria, and encephalocele have been reported [3].

The treatment of the disease is symptomatic and should be multidisciplinary. It usually includes physical therapy, adaptation of education to cognitive and behavioural aspects, and treatment of associated complications and symptoms [3]. The prognosis depends on the type of JS and the number of organic lesions.

Genetic counselling is very important due to the 25% risk of recurrence in autosomal recessive hereditary forms. Prenatal detection is possible by ultrasound from 11–12 weeks and cerebellar anatomical evaluation with MRI between 20–22 weeks of gestation [2].

Children with nystagmus, intellectual deficit, and ataxia should undergo a comprehensive ocular examination and neuroimaging [2]. 

All patient data have been completely anonymised throughout the entire manuscript and related files.