Smith-Magenis Syndrome (SMS) is a developmental disorder with patterns of physical, behavioral, and developmental features which occur due to a deletion of chromosome 17. It affects approximately 1:25,000 people, although researchers believe the number is actually closer to 1:15,000. SMS is sometime misdiagnosed as Down syndrome, Fragile X, Williams syndrome, Velocardiofacial syndrome (VCFS), or DiGeorge syndrome, and is one explanation for the discrepancy in the statistics. There are at least 600 diagnosed cases of SMS, the majority of which have been identified in the last few years as a result of more accurate genetic testing. As awareness about this rare syndrome increases, so do the number of diagnoses. Smith-Magenis Syndrome is alternatively known as 17p 11.2 monosomy, 17p syndrome, or chromosome 17p deletion syndrome.
- Distinct facial features which become more prominent as individual matures: square-shaped face, rosy cheeks, deep-set eyes, flat bridge of nose, mouth turned downward
- Mild to moderate intellectual disability
- Delayed speech and language skills
- Sleep disturbances
- Behavioral problems: anxiety, aggression, self-injury (such as head banging or skin picking), self-hugging (which some consider as a unique trait to SMS), compulsive behaviors (such as hand licking and page flipping, or hand squeezing), temper tantrums, hyperactivity, sudden mood shifts
- Short, broad hands
- Hoarse voice, hypernasal speech
- Eye abnormalities resulting in vision problems
- Reduced sensitivity to pain and temperature
- Dental abnormalities
- Distinct broad-step manner of walking
- Positive behavioral characteristics: affectionate, good sense of humor, excellent long-term memory, charming personalities
Smith-Magenis Syndrome was first identified in 1982 by Ann C. M. Smith, MA, DSc, a genetic counselor and Dr. R. Ellen Magenis, a chromosome expert. SMS is caused by a missing piece of genetic material from chromosome 17, referred to as deletion 17p11.2. The deleted genes encompass approximately 25 genes, including the RAI1 (Retenoic Acid Inducible 1) gene. In 90% of cases SMS is caused by a deletion of RAI1 and in 10% of cases it is caused by a mutation of RAI1. The different sizes of the deletions contribute to phenotypic variation in SMS.
The deletion of genetic material is not usually passed on from parent to child. SMS results from a genetic change that occurs during the formation of reproductive cells or in early fetal development.
Diagnosis & Treatment
As a result of the low number of known patients with SMS, many doctors are not aware of the disorder. A geneticist can perform a chromosome analysis through a blood test. The FISH (Flurorescence In Situ Hybridization) test maps genetic material in a person’s genes and can produce a more accurate detection of SMS. Newly diagnosed patients are also encouraged to undergo screenings for other possible issues with major body systems such as the heart, kidneys, eyes, and skeletal anomalies.
Currently there is no cure for SMS; however, certain types of medication can help with some of the behavioral symptoms. Some parents use psychotropic medications to help stabilize their child’s emotional mood swings, decrease hyperactivity, and reduce anxiety.
Research suggests that the sleep disturbances which cause SMS patients to experience lethargy during the day and restlessness at night, is related to an inverted melatonin cycle. Ingesting the hormone melatonin can sometimes help regulate sleep patterns, which as a result, may also help with other maladaptive behaviors such as aggression and attention problems.
Generally, researchers estimate that individuals with SMS have a normal life expectancy. They can achieve semi-independence with the help of a strong support system from family, school, work, and service providers. The severity of the disorder depends on the size of the genetic deletions. While some patients with SMS experience few symptoms and exhibit few maladaptive behaviors, others have multiple system failures.
New medications provide positive results to improve quality of life. Researchers continue to examine the complexities of the disorder, as well as its relationship to the reciprocal disease of SMS, known as Potocki-Lupski Syndrome (PTLS). SMS results from a deletion of chromosome 17p11.2, whereas PTLS results from a duplication of chromosome 17p11.2.
Information about SMS is still emerging, but this rare disorder is slowly gaining attention. ABC News did a story about it in 2010 which can be viewed here: SMS: Families Struggle. There are a handful of parents who have a child with SMS who have written about their experiences in online blogs. Take a look at Tales from the Trenches and read about young Garrett who was diagnosed at 18 months. For more information, educational videos, or to connect with other parents and advocates, go to the Parents and Researchers Interested in Smith-Magenis Syndrome (PRISMS) website, the Taylor Bug Kisses Foundation website, or the SMS Research Foundation website.