Smith-Magenis Syndrome
A rare genetic condition with a famous quirk: the body clock runs upside down. Children with SMS are often warm and funny, and their families juggle big sleep and behaviour challenges with remarkable grace.
Quick answer: Smith-Magenis syndrome (SMS) is a rare genetic condition, affecting about 1 in 15,000 to 25,000 people, caused by a small deletion on chromosome 17 (17p11.2) or a change in the RAI1 gene. It brings developmental delay, sleep problems from an upside-down melatonin rhythm, and behaviour challenges. There’s no cure, but specialist sleep care, therapies and family support make a big difference.
Smith-Magenis Syndrome Awareness Day is 17 November, a nod to chromosome 17, during SMS Awareness Month.
How common. About 1 in 15,000 to 25,000 babies are born with SMS. It affects boys and girls equally, and many people are thought to be undiagnosed.
The genetics.
- About 9 in 10 people have a small missing piece (deletion) of chromosome 17, at a spot called 17p11.2.
- About 1 in 10 have a change in a single gene in that region, RAI1, instead; newer studies suggest this may be more common than thought.
- RAI1 helps run the body clock and many other genes, which is why it causes so many of the features.
- It usually happens by chance and isn’t inherited from a parent. Nothing a parent did causes it.
- It’s confirmed with a genetic test, such as a chromosome microarray, or gene testing for RAI1. A genetic counsellor can explain what it means for the family.
The upside-down body clock
Melatonin is the hormone that tells the body it’s night. In most people with SMS its rhythm is flipped: it’s released in the daytime and is low at night.
- Sleep problems are nearly universal and start early: trouble settling, waking often and very early, and sleepiness during the day.
- Daytime sleepiness can show up as tiredness, irritability or more outbursts, not just napping.
- Sleep loss is exhausting for the whole family, and getting help is a priority, not a luxury.
How it’s managed. Sleep care is led by a paediatrician or sleep specialist who knows SMS. In general terms:
- Consistent routines, a dark, calm bedroom, no screens before bed and no caffeine.
- Melatonin in the evening, timed to help sleep start at night.
- Sometimes a morning medicine (a type of beta blocker) to switch off the daytime melatonin, used together with evening melatonin.
- A safe sleep space, as night waking and wandering are common.
- Doses and timing are set individually by the specialist. Don’t start or change them without advice.
Other features
- Developmental delay and mild to moderate intellectual disability, with delayed speech
- Low muscle tone and feeding difficulties as a baby, later short stature
- A broad, square face and deep-set eyes, which become clearer with age
- A hoarse, deep voice; ear infections and hearing loss
- Short-sightedness and other eye problems, scoliosis, dental problems, constipation
- Reduced sensitivity to pain and temperature
- Less often: heart or kidney differences, and seizures
Behaviour, described kindly
Many people with SMS are warm, affectionate, funny and eager to please, often with an excellent long-term memory. Behaviour is part of the syndrome, not a parenting failure, and it usually has a reason: tiredness, frustration, anxiety or pain.
- Big feelings: tantrums, outbursts and mood swings, often worse when tired. Emotional age can lag well behind learning ability.
- Attention difficulties, impulsiveness and anxiety. Autism, ADHD or OCD are sometimes diagnosed alongside.
- Self-injury, such as hand-biting, head-banging or skin and nail picking, is very common (in over 95%). Reduced pain sensitivity plays a part.
- Characteristic habits: an excited upper-body self-hug (in about half), and “lick and flip” page turning.
- What helps: predictable routines, visual schedules, warning before changes, plenty of one-on-one attention, and positive behaviour support from people who know SMS.
Care and support
- A paediatrician coordinates care, with speech, occupational and physiotherapy, psychology and special education.
- Regular checks of hearing, eyes, spine and teeth are usually part of care.
- In Australia, the NDIS may fund therapies and supports once the diagnosis is confirmed.
- Parents and siblings need support too; respite and family groups make a real difference.
Support organisations.
- Smith-Magenis Syndrome Australia: national family support network, with family camps and help navigating services
- PRISMS (Parents and Researchers Interested in Smith-Magenis Syndrome, US): webinars, family support and an annual conference
- Genetic Alliance Australia and the Genetic Support Network of Victoria
See your GP or paediatrician if
- Sleep problems are wearing the family down
- Behaviour changes suddenly, which can be a sign of pain, illness or constipation
- You notice hearing or vision changes
- You need a referral, an NDIS plan review, or carer support
Get urgent help: call 000 (Australia) or your local emergency number for a seizure lasting more than 5 minutes, a serious injury, or if anyone is in danger. Head-banging can cause retinal detachment: sudden flashes, new floaters or a shadow over vision need same-day eye care.
Outlook. SMS is lifelong. With good sleep care, the right supports and understanding, children with SMS grow into adults who keep learning and enjoying life, and many families describe them as the heart of the household.
Common questions
What causes Smith-Magenis syndrome?
About 9 in 10 people have a small deletion on chromosome 17 (17p11.2); most others have a change in the RAI1 gene in that region. It usually happens by chance and isn’t inherited.
Why do people with SMS sleep so badly?
In most people with SMS the sleep hormone melatonin is released in the day instead of at night, an upside-down body clock. It causes night waking, very early waking and daytime sleepiness.
How is sleep managed in Smith-Magenis syndrome?
A specialist usually combines good sleep routines with evening melatonin, and sometimes a morning medicine that blocks daytime melatonin. Doses are set individually, so don’t start or change them without advice.
Is challenging behaviour part of SMS?
Yes. Outbursts, anxiety and self-injury are common features of the syndrome, often worse with tiredness, and they’re not caused by parenting. Routines, positive behaviour support and better sleep help.
How common is Smith-Magenis syndrome?
About 1 in 15,000 to 25,000 births, affecting boys and girls equally. Many people are probably undiagnosed.
Where can families get support?
Smith-Magenis Syndrome Australia and PRISMS offer family support, information and events. Genetic counsellors and the NDIS can help too.
When is Smith-Magenis Syndrome Awareness Day?
17 November, a nod to chromosome 17, during SMS Awareness Month.
Evidence and more information
- MedlinePlus Genetics: Smith-Magenis syndrome
- Rinaldi et al, Genes 2022: Smith-Magenis syndrome, clinical review, biological background and related disorders
- De Leersnyder et al, J Med Genet 2001: β1-adrenergic antagonists improve sleep and behavioural disturbances in Smith-Magenis syndrome
- Raising Children Network: Smith-Magenis syndrome
- Smith-Magenis Syndrome Australia (organisation profile)
- PRISMS (directory listing)
- Firefly: Smith-Magenis Syndrome Awareness Day, 17 November
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