Smith-Magenis syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Smith-Magenis syndrome is a developmental disorder that affects behavior, emotions, and learning processes. The major features of this condition include distinctive facial features, sleep disturbances, behavioral problems, mild to moderate intellectual disability, and delayed speech and language skills.

Most people with Smith-Magenis syndrome have a broad, square-shaped face with deep-set eyes, full cheeks, and a prominent lower jaw. The middle of the face and the bridge of the nose often appear flattened. The mouth tends to turn downward with a full, outward-curving upper lip. These facial differences can be subtle in early childhood, but they usually become more distinctive in later childhood and adulthood. Dental abnormalities are also common in affected individuals.

Disrupted sleep patterns are characteristic of Smith-Magenis syndrome, and they typically begin early in life. Affected people may have trouble falling asleep at night and awaken several times during the night and early morning. They may be very sleepy during the day.

People with Smith-Magenis syndrome typically have affectionate, engaging personalities, but most also have behavioral problems. These include frequent temper tantrums and outbursts, aggression, anxiety, impulsiveness, and difficulty paying attention. Self-injury, including biting, hitting, head banging, and skin picking, is very common. People with Smith-Magenis syndrome may have other behaviors, such as repetitive self-hugging or compulsively licking their fingers and flipping pages of books and magazines (a behavior known as "lick and flip").

Other signs and symptoms of Smith-Magenis syndrome include short stature, abnormal curvature of the spine (scoliosis), obesity, and a hoarse voice. Some people with this disorder have ear abnormalities that lead to hearing loss. Affected individuals may have eye abnormalities that cause nearsightedness (myopia) and other vision problems. Although less common, heart and kidney defects also have been reported in people with Smith-Magenis syndrome.

ORPHANET DEFINITION A rare, genetic, neurodevelopmental disorder characterized by cognitive impairment of variable severity, behavioral abnormalities, and sleep disturbance. Patients present with distinctive physical features and a wide range of malformations (e.g. cardiac, renal).

Inheritance

From: MedlinePlus Genetics, National Library of Medicine

Not inherited

Frequency in the source

From: MedlinePlus Genetics, National Library of Medicine

Point prevalence: 1-9 / 100 000; Europe; Value and class.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormal pineal melatonin secretion · Very frequent (99-80%)

An anomaly in the amount or timing of melatonin secretion by the pineal gland. Note that melatonin is also synthesized by multiple tissues outside of the pineal gland.

Abnormal repetitive mannerisms · Very frequent (99-80%)

Use of the same abnormal action in response to certain triggers or at random. They may be used as a way to regulate one's internal state but must otherwise have no apparent functional purpose.

Abnormality of speech or vocalization · Very frequent (99-80%)

An abnormality in the sound (volume) or cadence (rate) of speech.

Abnormality of the dentition · Very frequent (99-80%)

Any abnormality of the teeth.

Anxiety · Very frequent (99-80%)

Intense feelings of nervousness, tension, or panic often arise in response to interpersonal stresses. There is worry about the negative effects of past unpleasant experiences and future negative possibilities. Individuals may feel fearful, apprehensive, or threatened by uncertainty, and they may also have fears of falling apart or losing control.

Attention deficit hyperactivity disorder · Very frequent (99-80%)

Attention deficit hyperactivity disorder (ADHD) manifests at age 2-3 years or by first grade at the latest. The main symptoms are distractibility, impulsivity, hyperactivity, and often trouble organizing tasks and projects, difficulty going to sleep, and social problems from being aggressive, loud, or impatient.

Brachycephaly · Very frequent (99-80%)

An abnormality of skull shape characterized by a decreased anterior-posterior diameter. That is, a cephalic index greater than 81%. Alternatively, an apparently shortened anteroposterior dimension (length) of the head compared to width.

Brachydactyly · Very frequent (99-80%)

Digits that appear disproportionately short compared to the hand/foot. The word brachydactyly is used here to describe a series distinct patterns of shortened digits (brachydactyly types A-E). This is the sense used here.

Broad forehead · Very frequent (99-80%)

Width of the forehead or distance between the frontotemporales is more than two standard deviations above the mean (objective); or apparently increased distance between the two sides of the forehead.

Deeply set eye · Very frequent (99-80%)

An eye that is more deeply recessed into the plane of the face than is typical.

Delayed eruption of primary teeth · Very frequent (99-80%)

Delayed tooth eruption affecting the primary dentition.

Delayed speech and language development · Very frequent (99-80%)

A degree of language development that is significantly below the norm for a child of a specified age.

Depressed nasal bridge · Very frequent (99-80%)

Posterior positioning of the nasal root in relation to the overall facial profile for age.

Frontal bossing · Very frequent (99-80%)

Bilateral bulging of the lateral frontal bone prominences with relative sparing of the midline.

Other findings in the same source

From: Orphanet

Additional reported features include Global developmental delay (Very frequent (99-80%)); Hoarse voice (Very frequent (99-80%)); Hyporeflexia (Very frequent (99-80%)); Hypotonia (Very frequent (99-80%)); Intellectual disability (Very frequent (99-80%)); Midface retrusion (Very frequent (99-80%)); Obesity (Very frequent (99-80%)); Recurrent otitis media (Very frequent (99-80%)); Self-injurious behavior (Very frequent (99-80%)); Sleep abnormality (Very frequent (99-80%)). This is a selected summary, not a complete description of the condition.

When it may begin

From: MedlinePlus Genetics, National Library of Medicine

Adolescent; Adult; Childhood; Infancy; Neonatal

Inheritance in the source

From: MedlinePlus Genetics, National Library of Medicine

Not inherited

Frequency and the population described

From: MedlinePlus Genetics, National Library of Medicine

Point prevalence: 1-9 / 100 000; Europe; Value and class.

Which doctor should you see?

The suggested department for discussing Smith-Magenis syndrome is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Smith-Magenis syndrome. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.