Smith-Magenis syndrome (SMS) is a rare condition that is associated with developmental delay, learning difficulties, behavioural difficulties and a disturbed sleep pattern. SMS was first described by Ann Smith and colleagues in 1982. About 1 in 25,000 children are born with this condition, and it is probably under diagnosed. It is caused by a small deletion (microdeletion) on chromosome 17 (17p 11.2), which can be detected cytogenetically and/or by a special diagnostic test called Fluorescent in situ hybridisation (FISH) analysis.

Most children with SMS have developmental delay and moderate to severe learning difficulties. In infancy low muscle tone, feeding difficulties, failure to thrive and frequent ear infections are common. Speech delay tends to be more pronounced than motor delay, and language comprehension is more impaired than expression.

The most distinctive features of SMS are the behavioural problems. These include self-injurious behaviours such as hand biting, self-pinching or scratching, picking at sores, hitting the head or body, and tearing or picking fingernails or the skin around the nails. Some affected patients also demonstrate 'self-hugging' and 'lick and flip' (licking their fingers and rapidly flicking the pages of a book) behaviours. Other behavioural problems include aggression, frequent temper tantrums, hyperactivity, restlessness and distractibility, and severe sleep disturbance, including difficulties falling asleep, shortened sleep cycles, frequent and prolonged night waking and early morning waking. These abnormalities and a phase shift of the circadian rhythm of melatonin are suggestive of an underlying biological clock problem in the syndrome. Autistic-type behaviours such as resistance to change, repetitive questioning, and preoccupations with particular topics are also common.

In many cases the severe behaviour difficulties in children with the syndrome persist into adulthood. Some individuals show improved behaviour with age, but others show a worsening of the aggression and self injury or no change. At the same time, people with SMS are often described as loving and caring, eager to please and with a good sense of humour. They love adult attention and enjoy interacting with adults.

Facial features of SMS are fairly distinctive and include a flat, broad head and prominent forehead, heavy brows, up-slanting eyes, depressed nasal bridge, and a wide mouth with fleshy and inverted central portion of the upper lip. Other features include a relatively hoarse, deep voice, short stature, eye problems (squint and iris abnormalities), hearing loss and scoliosis (spinal curvature). Congenital heart disease, epilepsy and kidney abnormalities are less consistent features. Clinical signs of peripheral neuropathy are found in seventy-five per cent of individuals, and include decreased sensitivity to pain and temperature, gait disturbances and muscle weakness.

The characteristic behaviour and sleep disturbance coupled with the distinctive facial features often suggest the diagnosis, which can be confirmed by FISH analysis to look for the 17 p 11.2 microdeletion.

Inheritance patterns
Most cases of SMS are sporadic in origin. Rarely, the 17p11.2 microdeletion may arise in a child because one of the parents might carry a "balanced" rearrangement involving this region of the short arm of one chromosome 17. Therefore, if the diagnosis of SMS is confirmed in a child the parents' chromosomes should also be checked. If the parental chromosomes are normal then the recurrence risk of SMS is likely to be very small.

Prenatal diagnosis
Parents of children with SMS can be offered prenatal diagnosis in future pregnancies. This involves chorionic villus sampling (CVS) between eleven to thirteen weeks gestation, or amniocentesis between fifteen to sixteen weeks gestation, followed by FISH analysis to look for the 17p11.2 microdeletion.

Medical text written July 2003 by Contact a Family. Approved July 2003 by Dr J Tolmie, Consultant Clinical Geneticist, Duncan Guthrie Institute of Medical Genetics, Glasgow, UK. Last reviewed January 2004 by Dr M Suri, Consultant Clinical Geneticist, City Hospital, Nottingham, UK. Additional material provided by Dr O Udwin, Consultant Clinical Child Psychologist, West London Mental Health NHS Trust, London, UK.

Further Online Resources
Medical texts in The Contact a Family Directory are designed to give a short, clear description of specific conditions and rare disorders. More extensive information on this condition can be found on a range of reliable, validated web sites and links to them are included in the CD-ROM version of this Directory. Further information on these resources can be found in our Medical Information on the Internet article.

SMITH-MAGENIS FOUNDATION

Smith-Magenis Foundation
24 Brook Road
Dersingham
King's Lynn
Norfolk PE31 6LG
Tel: 01328 730782
e-mail: info@smith-magenis.co.uk
Web: http://www.smith-magenis.co.uk

The Foundation is a National Registered Charity No. 1072573, established in 1992. It offers support by letter, email and telephone. It also aims to raise awareness of the condition. It publishes a newsletter and has information available, details on request. The Foundation has over 100 families in membership.

Group details last updated November 2007.