Smith-Magenis syndrome is a genetic disorder characterized by intellectual disability, sleep disturbances, behavioural abnormalities and distinctive facial features. Some people experience hearing problems, vision problems, scoliosis, and organ defects. Such signs, symptoms and severity vary from one affected individual to another.
At least 1 in 25,000 people worldwide are affected by Smith-Magenis syndrome. The article “Smith-Magenis syndrome” on the Genetics Home Reference website notes that it is likely to be under-diagnosed. There is currently no cure, and so any treatment is focused on managing the disorder and any complications arising.
Genes Involved in Smith-Magenis Syndrome
People with Smith-Magenis syndrome are usually missing a piece of the short (p) arm of chromosome 17 in their somatic (body) cells. This is called a chromosomal deletion. The function of the missing genetic material is not clear, but it is likely that the absence of a gene called retinoic acid induced 1 (RAI1) causes the majority of signs and symptoms.
When genetic material is missing, this means a protein or proteins aren’t being made or are impaired. More rarely, Smith-Magenis syndrome is caused by a mutation solely in the RAI1 gene. People affected by this version may experience fewer signs and symptoms than people affected by the chromosomal deletion.
Is Smith-Magenis Syndrome Inherited?
Smith-Magenis syndrome usually doesn’t run in families, and is the result of a spontaneous change. This is often the case with chromosomal disorders. Such changes can take place when eggs and sperm are made. Random changes can also happen after fertilization, when a fetus is in the early stages of development.
Genetic Testing and Smith-Magenis Syndrome
A chromosome analysis can identify the deletion associated with Smith-Magenis syndrome, and prenatal testing is sometimes available. A mutation in the RAI1 gene can also be detected with testing. Genetic counseling may be an option for people who require support and information on genetics-related health issues.
Visit the Parents and Researchers Interested In Smith-Magenis Syndrome website for more information on the disorder, including details on diagnosis and management. For more information on chromosomes and chromosomal disorders, read Introduction to Chromosomes in Human Cells and Introduction to Chromosome Abnormalities.
Sources
“Smith-Magenis Syndrome”, published: 2008, European Journal of Human Genetics (Orphanet) website accessed: 5th September 2010, author: Elsea, Sarah and Girirajan, Santhosh.
“Smith-Magenis Syndrome”, last updated: 7th January 2010, GeneReviews (NCBI) website, accessed: 5th September 2010, authors: Smith, Ann CM (et al).
“Smith-Magenis syndrome”, published: 30th August 2010, Genetics Home Reference website, accessed: 5th September 2010, no author specified.
“Smith-Magenis syndrome”, published: July 2003, Orphanet website, accessed: 5th September 2010, authors De Leersnyder, Hélène and Munnich, Arnold.
Barbara Melville - Popular introductory articles: Useful Science Basics for Understanding GeneticsUseful Science Basics for Understanding EvolutionBasic ...
