Smith-Magenis Syndrome

Medically Reviewed by Dan Brennan, MD on March 05, 2023
4 min read

Smith-Magenis syndrome (SMS) is a developmental disorder that affects several parts of the body. About 1 in every 25,000 people around the world have it. But experts think it may be closer to 1 in 15,000 since many cases aren’t diagnosed.

Some symptoms are present at birth, but others show up later. These can include:

  • Unique physical features
  • Behavioral problems
  • Learning difficulties

Most SMS cases are caused by missing parts of chromosome 17, specifically a gene called RAI1. In other cases, the RAI1 gene is there but has mutated, or changed. It’s possible other genes play a role in the condition, but more research is needed.

SMS typically isn’t something you get from your parents. Most people have no family history of the disease. Instead, the changes happen randomly in the egg or sperm, or in the baby before birth. Very rarely, a portion of your mother’s or father’s chromosome 17 moves from its normal spot to another position.

There are many, but it depends on the person. Physical signs of SMS can include:

  • A short, flat head
  • A large forehead
  • A broad, square face
  • Deep-set eyes
  • A short nose
  • A small chin that gets bigger with age
  • Being unusually short

Dental problems are also possible. These include:

  • Missing permanent teeth
  • Taurdautism (large teeth with smaller roots)
  • Macroglossia (large tongue)
  • Bruxism (teeth grinding)

Common physical symptoms include:

  • Repeated ear and sinus infections
  • Hearing problems
  • Eye problems, such as being near-sighted
  • Voice box and vocal cord problems
  • Problems with lip, tongue, and jaw muscle movement
  • Weight gain
  • Scoliosis (curved spine)
  • Less sensitivity to pain and temperature

Babies with SMS often have poor muscle tone and reflexes. They sometimes have a hard time sucking, so they don’t always get the nutrients they need. Because of this, they may not grow or gain weight as fast as children who don’t have the disorder. Babies with SMS also tend to sleep longer and are lethargic, or don’t have a lot of energy.

But as they get older, children with SMS often have trouble sleeping, which can stay with them into adulthood. They may find it hard to fall asleep, wake up often at night, and be extra sleepy during the day.

Many children with SMS are slower to reach speech and other developmental milestones. Infants tend to cry less and don’t make much noise in general.  Adults can have anywhere from mild to moderate intellectual disability.

Behavioral problems typically show up as they age. These can include:

  • Head banging
  • Hugging themselves a lot
  • Poor impulse control
  • Hyperactivity and difficulty paying attention
  • Tantrums, moodiness, aggression
  • Self-injury, such as biting or picking at skin

But people with SMS also tend to have a great sense of humor and very good long-term memory.

A blood test that checks chromosomes can tell you whether you or your child have SMS.

It’s always good to write down things to ask your doctor so you don’t forget. These could include:

  • How is SMS affecting me or my child’s body and development?
  • What are the treatment options?
  • How do I find resources like physical therapy?
  • What can I do to help my child at home or make things easier for myself?
  • Are there certain symptoms I should keep an eye on?
  • What can I expect to change over time as I or my child ages?

Treatment depends on the symptoms but will likely be a team effort involving several health care professionals. These may include:

  • Pediatricians
  • Surgeons
  • Cardiologists (heart doctors)
  • Dental specialists
  • Speech pathologists
  • Audiologists (hearing specialists)
  • Ophthalmologists (eye doctors)
  • Psychologists

The earlier in childhood you start the better. For example, speech, occupational, and physical therapy can help your child get better with certain things. Job training, sensory therapy, and other services can help with the challenges of daily life. Certain medications may ease behavioral problems and help with sleep. But it’s never too late: Even if you’re an adult with SMS, these therapies can help you better manage challenges related to your condition.

It's important to remember that each person with SMS is unique. If your baby has the disease, you’ll likely need extra support from your family and friends. But with the help of experts, your child can learn and grow, enjoy hobbies, get a job, and gain some independence. To learn more about what to expect, talk to your child’s doctor about their specific situation.

Taking care of someone with SMS can sometimes be stressful. You may be keeping up with several doctors and other health care professionals. And the behavioral issues that often come with SMS can be difficult to manage. You can’t do it alone. It’s important to ask your friends and family for help and take time for yourself.

If you have SMS, you’re likely well aware of the ways it’s affected your life. You may seem to age faster than others, but you’ll likely live just as long. Certain medical problems may worsen over time, but that can happen with anyone. However, your mental abilities will stay just as strong as they have been. As an adult, you’ll likely still need extra help with daily activities and self-care, or live at home with your family. Being informed about your options is key.

There are many groups ready to offer support if you or your child has SMS. Among them are:

Show Sources


Genetic and Rare Diseases Information Center: “Smith-Magenis Syndrome.”

MedlinePlus: “Smith-Magenis syndrome.”

National Organization for Rare Disorders: “Smith Magenis Syndrome.”

PRISMS: “What Is SMS?”

Smith-Magenis Syndrome Foundation UK: “What is SMS?”

Udwin, O. "Outcomes in Neurodevelopmental and Genetic Disorders," Cambridge University Press, 2002.

View privacy policy, copyright and trust info