Information on the following diseases can be found in the Related Disorders section of this report:

• Dandy Walker Syndrome
• Leber's Congenital Amaurosis
• Hydrocephalus

Joubert Syndrome is characterized by periods of cessation of breathing during sleep (sleep apnea). Periods of deep, abnormal breathing are common in infants and may be triggered by emotional stimulation such as crying. Unusually deep inhalations also occur. These respiratory irregularities generally decrease as the infant gets older.

Abnormal eye movements such as irregular jerking, eye rolling or crossing of the eyes may be present. Impaired coordination of movement and walking (ataxia), and difficulty in controlling the range of voluntary movement (dysmetria) are characteristic of Joubert Syndrome. Tremors may also be observed. Muscle weakness may be accompanied by clumsy or rapid alternating movements. Mental retardation may also occur.

The exact cause of Joubert Syndrome is not known. This disorder may be inherited as an autosomal recessive trait. Human traits, including the classic genetic diseases, are the product of the interaction of two genes, one received from the father and one from the mother. In recessive disorders, the condition does not appear unless a person inherits the same defective gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk of transmitting the disease to the children of a couple, both of whom are carriers for a recessive disorder, is 25 percent. Fifty percent of their children risk being carriers of the disease, but generally will not show symptoms of the disorder. Twenty-five percent of their children may receive both normal genes, one from each parent, and will be genetically normal (for that particular trait). The risk is the same for each pregnancy.

Joubert Syndrome is extremely rare and generally appears during infancy. It is estimated that only 10 cases occur each year in the United States. Both males and females can be affected, and the disorder can occur more than once in the same family.

Symptoms of the following disorders can be similar to those of Joubert Syndrome. Comparisons may be useful for a differential diagnosis:

Dandy-Walker Syndrome is a rare inherited disorder that is characterized by congenital hydrocephalus that is an accumulation of fluid in the brain and an increase of pressure within the skull. This swelling of the head is generally accompanied by headaches, visual disturbances that come and go and swelling of the eyes (papilledema). (For more information, choose "Dandy Walker" as your search term in the Rare Disease Database.)

Leber's Congenital Amaurosis (LCA) is a rare inherited disorder that affects the eyes. Infants are born without the cells that gather light in the retina of the eye. It is characterized by blindness at birth, roving eye movements and pupils that react poorly to light and dilate widely in darkness. Often the eyes are deeply set and the infant will rub the eyes to stimulate the retina to produce light (oculodigital stimulation). This disorder is frequently associated with a family history of loss of eye muscle coordination. (For more information on this disorder, choose "Leber's Congenital Amaurosis" as your search term in the Rare Disease Database.)

Hydrocephalus is a condition in which enlarged (dilated) cerebral ventricles in the brain restrict the normal flow of cerebrospinal fluid (CSF). The cerebrospinal fluid accumulates in the skull and puts pressure on the brain tissue. The characteristic features in children include an enlarged head, a bulging forehead, a thin transparent scalp and a downward gaze. Other symptoms may include convulsions, abnormal reflexes, a slowed heartbeat and respiratory rate, headache and visual problems. (For more information on this disorder, choose "Hydrocephalus" as your search term in the Rare Disease Database.)

The treatment for Joubert Syndrome is symptomatic and supportive. Special education services and physical therapy may be of benefit to children with this disorder. When hydrocephalus occurs, a shunt may be recommended to facilitate the drainage of fluid from the brain.

Genetic counseling may be of benefit for Joubert Syndrome families.

Research on birth defects and their causes is ongoing. The National Institutes of Health (NIH) is sponsoring the Human Genome Project that is aimed at mapping every gene in the human body and learning why they sometimes malfunction. It is hoped that this new knowledge will lead to prevention and treatment of genetic disorders in the future.

MENDELIAN INHERITANCE IN MAN, 10th Ed.: Victor A. McKusick, Editor: Johns Hopkins University Press, 1992. Pp. 1487.

BIRTH DEFECTS ENCYCLOPEDIA, Mary Louise Buyse, M.D., Editor-In-Chief; Blackwell Scientific Publications, 1990. Pp. 995-996.

JOUBERT'S SYNDROME WITH RETINAL DYSPLASIA: NEONATAL TACHYPNOEA AS THE CLUE TO A GENETIC BRAIN-EYE MALFORMATION, M.D. King et al.; Arch Dis Child (August 1984; 59(8)): Pp. 709-718.

DYSMORPHIC FEATURES OF JOUBERT SYNDROME, L.A. Squires et al.; Dysmorphol Clin Genet (May 1991; 5): Pp. 77-79.

JOUBERT'S SYNDROME ASSOCIATED WITH CONGENITAL FIBROSIS AND HISTIDINEMA, R.E. Appleton et al.; Arch Neurol (May 1989; 46(5)): Pp. 579-582.