Smith-Magenis syndrome


Smith-Magenis syndrome (SMS) is a genetic disorder that is characterized by varying degrees of intellectual disabilities (formerly called mental retardation), distinctive facial features, sleep disturbances, and behavioral problems. Symptoms are usually apparent shortly after birth. The disease is not considered progressive, but the distinct facial features are usually more noticeable once the patient reaches adolescence or adulthood.
SMS occurs when a person is born with a mutated retinoic acid-induced 1 (RAI1) gene or a missing region of chromosome 17. Most cases occur randomly during development and are not passed down among family members.
Researchers estimate that SMS affects at least one out of 25,000 people worldwide. However, many experts believe that the condition is often undiagnosed and misdiagnosed, because genetic tests for the disorder have only been available since the mid-1990s. Therefore, some believe that the prevalence may be closer to one out of 15,000 people. SMS affects males and females equally.
There is currently no cure for SMS. However, many treatments and therapies may help patients cope with the disorder. With proper therapy, some patients with intellectual disabilities are able to live independently once they become adults, while others may need lifelong support or residential care. Adults with profound intellectual disabilities usually require lifelong nursing care. However, it should be noted that most people with SMS have mild-to-moderate intellectual disabilities. Although there are limited data regarding the average life expectancy of someone with SMS, it has been reported that some people have lived to be older than 70 years of age.

Related Terms

17p syndrome, autism, behavioral therapy, childhood intervention programs, chromosomal deletion, chromosome 17, circadian rhythm, cognitive disabilities, developmental disorder, FISH analysis, fluorescence in situ hybridization, genetic mutation, high-resolution chromosome analysis, intellectual disabilities, learning disabilities, RAI1 gene, RAI1 protein, retinoic acid-induced 1 gene, SMCR, Smith-Magenis chromosome region, speech-language therapy.

types of the disease

The clinical presentation of Smith-Magenis syndrome (SMS) may vary according to the type of genetic change in chromosome 17. Dysfunction of the retinoic acid-induced 1 (RAI1) gene on chromosome 17 is related to the cardinal features (symptoms that lead to diagnosis) of SMS. Most cases of SMS are caused by a deletion in chromosome 17, though rare cases are related to a mutation in the RAI1 gene. People with SMS who have a genetic mutation in the RAI1 gene typically experience milder symptoms than people with a chromosomal deletion. People with genetic mutations are less likely to have hearing loss, heart defects, kidney abnormalities, and short stature.