Condition AZ: j
Also known as: Joubert-Boltshauser syndrome
Joubert syndrome is a rare neurological condition characterised by developmental delay, floppiness (see entry Hypotonia), ataxia (lack of muscle control) and difficulty controlling oculomotor apraxia (horizontal eye movements). Other symptoms include hyperpnea (abnormal breathing patterns), kidney abnormalities (see entry Kidney disease) and a characteristic facial appearance. Individuals with Joubert syndrome may show some or all of these features and their severity may vary. The major investigation finding is underdevelopment of the cerebellar vermis (a narrow, worm-like structure between the hemispheres of the cerebellum) and brain stem on a magnetic resonance imaging (MRI) scan.
Medical text written May 2003 by Contact a Family. Approved May 2003 by Professor M Patton, Professor of Medical Genetics, St George’s Hospital Medical School, London, UK. Last updated February 2010 by Professor Brian Neville, Emeritus Professor of Paediatric Neurology, UCL Institute of Child Health and Great Ormond Street Hospital, London, UK.
Hypotonia is particularly evident in the neonatal period (the period immediately after birth) and during infancy. Children may be moderately or severely affected and may lack head control, have difficulties rolling over, sitting, standing and walking. Unsteadiness due to ataxia and balance problems may also be present. Joubert syndrome also affects breathing and abnormal over breathing commonly occurs during the neonatal period. This may improve with age but, in some cases, it persists and may threaten survival.
Individuals with Joubert syndrome have abnormal eye movements including a squint with or without retinal degeneration, and with or without congenital blindness (see entry Vision disorders in Childhood). Young infants with Joubert syndrome often have a characteristic appearance with a large head, prominent forehead, high rounded eyebrows, broad nasal ridge, mild epicanthus, upturned nose with evident nostrils, open mouth and protruding tongue. This appearance becomes less pronounced as the child grows.
Cognitive and physical development is delayed in Joubert syndrome. Moderate-to-severe learning difficulties are common, language may be delayed. Some children with Joubert syndrome are hyperactive, combative and difficult to manage whilst others display normal behaviour.
Joubert syndrome may be caused by gene abnormalities in at least three ‘loci’ or specific locations on a gene that relate to subtypes of Joubert syndrome. Some have no identifiable gene defect. The cerebellar vermis is responsible for controlling posture, coordinating head and eye movements and fine-tuning muscles. The brain stem is responsible for maintaining the body’s involuntary functions, such as heartbeat, breathing, and thermoregulation. The cerebellar vermis and brain stem are underdeveloped or absent in individuals with Joubert syndrome. These changes may be identified on an magnetic resonance imaging (MRI) scan of the brain.
Treatment for Joubert syndrome is symptomatic (designed to alleviate the symptoms experienced by an individual with the condition) and supportive. Infant stimulation, physical, occupational, and speech therapy may have beneficial effects.
Joubert syndrome is inherited as an autosomal recessive trait.
Features of Joubert syndrome may sometimes be visualised by ultrasound scan by 18 to 20 weeks of pregnancy. If a specific gene defect is known, it can be identified.
Also known as: 11q Deletion syndrome
Jacobsen syndrome was first described in 1973 by a Danish geneticist, Dr Petrea Jacobsen. It is a rare chromosomal condition which affects about 1 in 100,000 births.
Medical text written September 2003 by Contact a Family. Approved September 2003 by Professor F Cotter. Last updated January 2010 by Professor F Cotter, Professor of Experimental Haematology, Department of Medical Oncology, Barts and the London School of Medicine and Consultant Haematologist, Barts and the London NHS Trust, London, UK.
Jacobsen syndrome is associated with a recognisable pattern of features. The children are usually of a pleasant disposition with a characteristic face, somewhat more pear shaped than normal. There may also be some developmental delay (learning difficulties, see entry Learning Disability), varying from mild to more severe. Speech and language may be slower. However, heart problems such as enlarged left heart syndrome (see entry Heart Defects) can be more debilitating, sometimes requiring surgery. Blood disorders, mainly in the form of easy bruising and prolonged bleeding due to low numbers of platelets (thrombocytopenia – reduction in the number of platelets present in the blood and referred to as Paris-Trousseau syndrome) are common. Gastrointestinal problems including pyloric stenosis (a narrowing of the outlet from the stomach to the small intestine) and frequent respiratory problems also are seen. Individuals with Jacobsen syndrome may show some or all of these features although there is great variability in the number and severity of symptoms.
The life expectancy for individuals with Jacobsen syndrome currently remains unknown but is increasing as we understand more about the symptoms and how to manage them. The two most common causes of illness and death are congenital heart defects and bleeding. The improved outcomes in children with most forms of congenital heart disease, however, suggest that the outcomes for children with Jacobsen syndrome with congenital heart defects is also likely to continue to improve.
It is caused by the loss of a small portion of a chromosome at conception. A chromosome is made up of DNA code in a thread-like structure present in the nucleus of most cells in the body. The DNA code in turn carries genes which are the all important instructions about how each cell in the body should divide, grow and die. Genes are ‘strung’ along chromosomes rather like beads are strung along a necklace. In each cell, there are 23 pairs of chromosomes. The body needs a full compliment of chromosomes for normal health and development. Sperm and ova (‘egg cells’) carry one representative of each chromosome and at fertilisation usually fuse to create a baby with the full number of chromosomes shared equally from both parents. In Jacobsen syndrome, a small piece of the 11th chromosome is deleted (or missing) and this causes a range of clinical features in individuals with this condition. The features are related to the genes that are absent from the small piece of chromosome 11 that is missing and the structure of the chromosome shows a fragility that causes a small point at the tip to break off and cause the symptoms. The reason for the loss of the piece of chromosome is not fully understood. Jacobsen syndrome occurs more frequently in females than males.
Jacobsen syndrome occurs sporadically. For this reason, it is unusual for any other member of the family, brother or sister, to be affected.
Information and support in the UK for Jacobsen syndrome is provided by Unique (see entry Chromosome Disorders).