Smith-Magenis syndrome (SMS)

What is Smith-Magenis syndrome?

Smith-Magenis syndrome is a genetic developmental disorder. Individuals usually display affectionate personalities but may also present with behavioral issues and repetitive behaviors. Delayed speech and language development, as well as issues with sleep are characteristic of the syndrome as well.

This rare disease affects multiple parts of the body and is characterized by distinct facial features. These unique facial features may be more subtle in infancy and childhood but generally become more pronounced with age.

Syndrome Synonyms:
Chromosome 17p11.2 Deletion Syndrome

What gene change causes Smith-Magenis syndrome?

The syndrome is caused by a deletion of the RAI1 gene on chromosome 17. It is inherited in an autosomal dominant pattern, but in many cases is the result of a new mutation.

In some cases, a genetic syndrome may be the result of a de-novo mutation and the first case in a family. In this case, this is a new gene mutation which occurs during the reproductive process.

In the case of autosomal dominant inheritance just one parent is the carrier of the gene mutation, and they have a 50% chance of passing it onto each of their children. Syndromes inherited in an autosomal dominant inheritance are caused by just one copy of the gene mutation.

What are the main symptoms of Smith-Magenis syndrome?

• The main symptoms of the syndrome include mild to moderate intellectual disability, delayed speech, issues with sleep, and potential behavioral issues.
• Self-injury and repetitive self-hugging are common symptoms unique to the syndrome, as is a behavior referred to as lick and flip- compulsive licking of the fingers, and of the flipping of the pages of books and magazines.
• Facial and physical characteristics include a short stature, hoarse voice, a broad and square face, deep-set eyes, full cheeks, a prominent lower jaw, downward-turned mouth and a flattened middle of the face and nose bridge.
• Other health conditions may include dental abnormalities, scoliosis, myopia, and a reduced sensitivity to pain and temperature.

Possible clinical traits/features:
Short nose, Neurological speech impairment, Myopia, Anteverted nares, Micrognathia, Morphological abnormality of the middle ear, Intellectual disability, Mandibular prognathia, Abnormal form of the vertebral bodies, Abnormal localization of kidney, Abnormal renal morphology, Autosomal dominant inheritance, Otitis media, Stereotypy, Pes planus, Toe syndactyly, Obesity, Open mouth, Hand polydactyly, Taurodontia, Seizure, Self-mutilation, Precocious puberty, Velopharyngeal insufficiency, Wide nasal bridge, Broad face, Brachycephaly, Broad palm, Cleft palate, Abnormality of the larynx, Abnormality of the immune system, Abnormality of the genital system, Abnormality of the forearm, Abnormality of the outer ear, Abnormality of the ureter, Abnormal tracheobronchial morphology, Abnormality of the tongue, Aplasia/Hypoplasia of the corpus callosum, Areflexia, Attention deficit hyperactivity disorder, Hoarse voice, Broad forehead, Hypercholesterolemia, Hyperacusis, Gait disturbance, Depressed nasal bridge.

How is Smith-Magenis syndrome diagnosed?

To find out if someone has a diagnosis of Smith-Magenis syndrome, it is important to have a consultation and evaluation with a clinical genetic specialist.  Specialists may also suggest specific genetic testing or other types of tests to help reach a diagnosis.  FDNA’s AI technology can help speed up the diagnostic process by analyzing facial features and other health information.