Joubert's syndrome

Joubert’s syndrome is a rare disorder affecting the brain, causing varying degrees of physical, mental and sometimes visual impairments.

With Joubert’s syndrome two parts of the brain (the cerebellar vermis and the brainstem) do not develop completely during pregnancy, due to a faulty gene. The cerebellar vermis is responsible for control of posture and muscles, and of head and eye movements. The brainstem controls functions such as heartbeat, breathing, and temperature control.

Underdevelopment or absence of the cerebellar vermis and the brainstem inevitably affects their functions. Some, but not yet all, causative genes have been identified.

Diagnosis is made by MRI brain scan appearances and can sometimes be confirmed by genetic testing on a blood sample.

The condition was first described by Dr Joubert in 1969. Prior to this, the various features seen in Joubert’s syndrome were not recognised as being a specific syndrome (group of symptoms with a single cause occurring in different people).

In some cases Joubert’s syndrome appears to be sporadic (just occurring in that particular individual), but it is more often inherited as an autosomal recessive disorder, which means that both parents are carriers of the disease.

Human beings have about 30,000 to 40,000 different genes, each of which has a function in making an individual person. The genes are arranged in pairs (one of the pair from each parent) on 23 chromosomes.

Inevitably some of these genes are faulty. A normal gene can overcome a faulty one, but if both genes in the pair are faulty, the genetic instructions cannot work. Most people carry different faulty genes but in Joubert’s syndrome (and other recessive conditions) parents, though healthy themselves, carry the same faulty genes, and risk passing them on to their children.

Each pregnancy carries

• a 25 per cent chance of the child being affected

• a 75 per cent chance of the child not being affected

The brain underdevelopment may be detected on fetal ultrasound performed at 18 to 20 weeks of pregnancy. If a specific gene has been identified in an affected child in the family, then this gene can be tested for in a blood sample.

There is no data available on incidence.

Children with Joubert’s syndrome can have very variable features and problems, from relatively mild to very severe. All babies are likely to have elements of the following:

• Many infants have a somewhat characteristic appearance, with a relatively large head, prominent forehead, broad nose and a tendency to keep their mouths open and their tongues out.

• Floppiness (hypotonia), unsteadiness (ataxia) and developmental or learning delay are present to some extent in all the children. The combination of these factors make sitting and standing delayed or very difficult to achieve.

• Jerky eye movements are likely to be obvious from early infancy and some babies will have very poor vision, or difficulty moving the eyes to look at an object (oculomotor apraxia).

• Learning difficulties are common, especially surrounding speech, and some children may be severely disabled and/or have difficult behaviour problems.

• Some children may develop epilepsy.

• Some children have kidney cysts, which may affect kidney function.

• An abnormal breathing pattern may be noticed soon after birth. This may improve with age but, sadly, very severely affected infants may die within the first few years of life from breathing problems. This is rare.

There is no treatment that can cure the underlying brain malformation and the resulting effects on the rest of the body. Medication may be given to help with the epilepsy if it occurs, and from the age of a few months, various therapies can be introduced and taught to parents to help the children achieve their maximum potential, both physically and intellectually.

When they reach school age, learning support and therapies can be integrated into their school day, and there are increasingly sophisticated methods of enhancing communication if speech is difficult to achieve.

Research is progressing rapidly in the genetic field, finding out what all the different genes are responsible for so that ‘faulty’ genes can be recognised. In some cases, this is already enabling earlier and more precise prenatal testing and this may, in the longer term future, lead to replacement of the faulty gene(s).

Unfortunately the brain underdevelopment could not be altered, so for children already affected, research ideas that concentrate on increasing the child’s developmental potential and independence are most important.

While medical treatment of any neurological disorder is very difficult because of the complexity of the brain, enormous strides are being made in the development of educational and therapy strategies and equipment.