A syndrome is a recognizable pattern of physical, behavioral, and developmental features that occur together in the same person due to a single, underlying cause. Smith-Magenis syndrome (or SMS) is a chromosomal disorder characterized by a recognizable pattern of physical, behavioral, and developmental features. It is caused by a missing piece of genetic material from chromosome 17, referred to as deletion 17p11.2.
Common features include: characteristic, yet subtle, facial appearance, infant feeding problems, low muscle tone, developmental delay, variable levels of intellectual disability, early speech/language delay, middle ear problems, skeletal anomalies and decreased sensitivity to pain. The syndrome also includes a distinct pattern of neurobehavioral features characterized by chronic sleep disturbances, arm hugging/hand squeezing, hyperactivity and attention problems, prolonged tantrums, sudden mood changes and/or explosive outbursts and self-injurious behaviors. For a more complete list of physical, developmental and behavioral characteristics, please click here.
Ann C.M. Smith, MA, DSc (Hon), a genetic counselor, and Dr. R. Ellen Magenis, a physician and chromosome expert, described the first group of children with this deletion in the 1980's. Most people with the diagnosis have been identified since 1995 as a result of improved laboratory techniques that allow the accurate detection of this chromosomal deletion. Although the exact incidence is not known, it is estimated that SMS occurs in 1 out of 25,000 births. SMS is under-diagnosed, but as awareness of it increases, the number of people identified grows every year.