Joubert syndrome

Joubert syndrome
ICD-10	Q04.3
ICD-9	742.2
DiseasesDB	30688

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Vamsikrishna Gunnam M.B.B.S [2]

Synonyms and Keywords: Cerebelloparenchymal disorder 4; Cerebellar vermis agenesis; Joubert-Boltshauser syndrome; JBTS1; CPD4; Cerebellooculorenal syndrome 1; CORS1; Joubert syndrome 1

Overview

Joubert syndrome is a rare genetic disorder that affects the areas of the cerebellar vermis and brain stem in the brain that controls balance and coordination. Joubert syndrome follows autosomal recessive pattern of inheritance. In The United States of America in order to categorise a condition as a rare disease it should affect fewer than 200,000 people. Rare diseases also called as orphan diseases. Orphan Drug Act was passed on 1983 by congress for the rare diseases. Today an average of 25-30 million americans have been reported with rare diseases. The number of people with individual rare disease may be less but overall the number of people with rare diseases are large in number.

Historical perspective

• Joubert syndrome was first discovered in in four siblings by Joubert et al in 1969.

Classification

• Joubert syndrome may be classified according to gene location of the mutation into 2 subtypes:

Phenotype	Location of mutation	Gene involved	Inheritance pattern
JOUBERT SYNDROME 1(JBTS1)	9q34.3	INPP5E	Autosomal recessive
JOUBERT SYNDROME 2(JBTS2)	11q12.2	TMEM216	Autosomal recessive

Pathophysiology

• It is understood that Joubert syndrome is the caused by mutation in INPP5E and TMEM216 gene on chromosome 9q34 and 11q12.2 respectively.

Presentation

The disorder is characterized by absence or underdevelopment of a part of the brain called the cerebellar vermis and a malformed brain stem (molar tooth sign). The most common features include ataxia (lack of muscle control), an abnormal breathing pattern called hypernea, sleep apnea, abnormal eye and tongue movements, and hypotonia. Other malformations such as extra fingers and toes, cleft lip or palate, tongue abnormalities, and seizures may also occur. There may be mild or moderate retardation.

Treatment

Treatment for Joubert syndrome is symptomatic and supportive. Infant stimulation and physical, occupational, and speech therapy may benefit some patients. Infants with abnormal breathing patterns should be monitored.

Prognosis

The prognosis for individuals with Joubert syndrome varies. Some patients have a mild form with minimal motor disability and good mental development, while others may have severe motor disability and moderate mental retardation.

Genetics

Multiple genes that are mutated in individuals with Joubert syndrome have been identified:

• Mutations in a gene of unknown function called AHI1 is associated with a subset of Joubert syndrome cases.

• In some rare cases of Joubert syndrome, mutations have been found in NPHP1 which is also associated with nephronophthisis, a cystic kidney disorder.

• The gene CEP290 has been associated with both Joubert syndrome and Leber's congenital amaurosis, type 10.