SNP Shot: Genomic Insights

Smith-Magenis syndrome (SMS) is a developmental condition impacting behavior, emotions, and the ability to learn. Key features of SMS include characteristic facial features, sleep problems, behavioral challenges, mild to moderate intellectual disability, and delays in speech and language development.

Individuals with SMS often have a broad, square face with deep-set eyes, full cheeks, and a prominent jaw. The central part of the face and the bridge of the nose may appear flattened. The mouth often curves downward, featuring a full, everted upper lip. These facial traits might be subtle in young children but become more pronounced as they age. Dental issues are also frequently observed in those affected.

Disrupted sleep patterns are a hallmark of SMS, typically emerging early in life. Individuals may struggle to fall asleep, wake up frequently during the night and in the early hours of the morning, and experience excessive daytime sleepiness.

While generally affectionate and engaging, individuals with SMS often exhibit behavioral difficulties. These can include frequent temper tantrums, aggression, anxiety, impulsivity, and attention deficits. Self-injurious behaviors, such as biting, hitting, head banging, and skin picking, are common. Other behaviors may include repetitive self-hugging or compulsive actions like licking fingers and flipping pages of books or magazines ("lick and flip").

Additional signs and symptoms of SMS can include short stature, scoliosis (spinal curvature), obesity, and a hoarse voice. Some individuals may have ear abnormalities resulting in hearing loss. Eye problems, such as nearsightedness (myopia) and other vision impairments, can also occur. Less frequently, heart and kidney defects have been reported.

Inheritance:

SMS is typically not inherited. It usually arises from a chromosomal deletion or a variation in the RAI1 gene occurring during the formation of eggs or sperm, or during early fetal development. Most individuals with SMS have no family history of the condition.

In rare instances, SMS is inherited from an unaffected mother who carries the genetic change only in her egg cells. This is known as germline mosaicism.