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Cohen syndrome

Also known as: Norio syndrome, Obesity-hypotonia syndrome, Pepper syndrome

Background

Cohen syndrome is a rare genetic condition characterised by moderate-to-severe learning difficulties (see entry Learning Disability), a typical facial appearance, early onset and progressive visual problems and neutropenia (low number of neutrophils in the blood). Other important features include a small head size (known as microcephaly), truncal obesity and over bendy joints.

Credits

Medical text written May 2011 by Dr K Chandler, Consultant Clinical Geneticist, North West Regional Genetic Service, St Mary's Hospital, Manchester, UK.

What are the symptoms?

As young babies, feeding difficulties are common in Cohen syndrome and some infants may need nasogastric tube feeding (where food is passed into the stomach via a tube in the nose). Some babies have stridor (noisy breathing), due to a floppy windpipe.

Young children with Cohen syndrome have developmental delay. They learn to walk later than the average child and their speech takes longer to develop. All children have special educational needs, with the majority attending schools for children with moderate-to-severe learning difficulties. Children with Cohen syndrome are typically very sociable and affectionate, however, a few can have behavioural difficulties that fall within the autistic spectrum (see entry Autistic Spectrum disorders, including Asperger syndrome).

From around ten years, children with Cohen syndrome put on more weight, especially around their tummies. However, they do not usually become generally obese. Many are short for their age and have microcephaly. Individuals with Cohen syndrome have loose, flexible joints and hypotonia (low muscle tone), which can result in difficulties with balance and coordination.

Children with Cohen syndrome often have a high roof to their mouth with overcrowding of their teeth. A specific feature of Cohen syndrome is a low number of white blood cells, called neutrophils, used by the body to fend off bacterial infections. Dental and skin infections may occur a little more frequently in some people with Cohen syndrome, however, it is rare to suffer from severe infections. Autoimmune disorders, in particular diabetes (see entry Diabetes Mellitus), thyroid disorders and coeliac disease, have been reported in some individuals.

Visual problems affect nearly all children with Cohen syndrome. These start during the preschool years with myopia (short-sightedness), which becomes more severe throughout childhood. In addition, the area at the back of the eye, known as the retina, gradually reduces in function causing poor vision in dim light and loss of the outer ranges of the visual field (known as a retinal dystrophy). Older children and adults with Cohen syndrome find it particularly difficult to see in reduced light or at night time and have 'tunnel vision'. Their visual acuity (close vision), however, usually remains quite good. By adult life, many people with Cohen syndrome are registered partially-sighted or blind.

Adults with Cohen syndrome usually continue to live at home or in residential care as their level of independence is limited. They are usually friendly people who enjoy socialising and group activities. They remain healthy and do not have a shortened lifespan.

What are the causes?

Cohen syndrome is caused by mutations in VPS13B also known as COH1. This gene lies on chromosome 8.

How is it treated?

There is no 'cure' for Cohen syndrome. Support for visual dysfunction should include the use of low-vision aids and regular ophthalmic follow-up. Early intervention and physical, occupational and speech therapy can help address developmental delay, flexible joints and hypotonia. Granulocyte-colony stimulating factor (G-CSF) may be considered for treating neutropenia in patients who have recurrent, severe infections.

Dental and skin infections are managed in the normal way. Overcrowding of teeth, may result in some teeth being removed.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
Cohen syndrome is an autosomal recessive condition. It is caused by a double dose of a change in the Cohen syndrome gene. Both parents of an affected child with Cohen syndrome will carry one copy of the altered gene but also have a normal copy, so they are not affected. Each time they have a baby, there is a 25 per cent chance of having an affected child.

Prenatal diagnosis
Currently a gene test is not available in the UK. Prenatal diagnosis by chorionic villous sampling is possible in those families where the gene changes have already been identified, through research or non-UK laboratories.

Is there support?

There is no support group for Cohen syndrome in the UK. A support group outside of the UK exists for Cohen syndrome, please ring our helpline for details. Contact a Family's web-based linking service can be accessed at community.cafamily.org.uk