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Smith-Magenis Syndrome

Smith-Magenis Syndrome



Overview

Smith-Magenis syndrome is a developmental condition that affects several parts of your child’s body. Some of the main symptoms include abnormal cognitive development (intellectual disability), unique facial features, behavioral concerns and difficulty sleeping. Smith-Magenis syndrome occurs because a small piece of a chromosome, carrying an important gene, is deleted from your child’s DNA during embryonic development.

Smith-Magenis syndrome can affect anyone, as the genetic change occurs at the time of conception when the egg and sperm meet. There’s usually no history of the condition in your biological family line. This is known as a spontaneous or “de novo” mutation.

In rare cases, your child may inherit the condition from a biological parent who doesn’t have symptoms of the condition but has a genetic change in some of their sex cells but not all of their cells. This type of inheritance is called germline mosaicism.

Symptoms

Symptoms of Smith-Magenis syndrome affect multiple organ systems in your child’s body. They range in severity from mild to severe. Common symptoms include:

Abnormal cognitive development (intellectual disability).

Short stature.

Scoliosis.

Limited sensation of pain or temperature.

Raspy or hoarse voice.

Hearing and/or vision problems.

Excessive weight gain.

Symptoms that affect infants include:

Weight gain during adolescence.

Weak muscle tone.

Developmental delay.

Poor reflexes.

Feeding challenges.

Frequent crying.

Long naps and daytime drowsiness.

Although rare, severe cases of Smith-Magenis syndrome can affect the function of your child’s heart and kidneys. It can also cause seizures.

Facial features

People born with Smith-Magenis syndrome have characteristic facial features that become more apparent during middle childhood. These features include:

A square-shaped face.

Full cheeks.

Sunken eyes.

Downward slanting mouth (frown).

A flat nasal bridge.

Protruding of the lower jaw.

Some children and adults diagnosed with Smith-Magenis syndrome have dental abnormalities due to their facial structure.

Sleep disturbances

Smith-Magenis syndrome can make sleeping difficult for infants, children and adults diagnosed with the condition. Sleep disturbances include:

Difficulty falling asleep and staying asleep.

Excessive daytime sleepiness.

Frequent nighttime awakenings.

The change in sleep patterns relates to melatonin secretion in individuals with Smith-Magenis syndrome.

Emotional or behavioral symptoms

Children diagnosed with Smith-Magenis syndrome can display certain emotional or behavioral symptoms, including:

Affectionate personality.

Self-hugging.

Frequent tantrums or outbursts.

Aggression (hand/wrist biting, head banging, hitting).

They may also have conditions that affect their behavior like ADHD or autism spectrum disorder.

Causes

Changes to the retinoic acid-induced 1 gene (RAI1) cause Smith-Magenis syndrome. The RAI1 gene is responsible for producing proteins that give your cells instructions to do their job throughout your body. This gene isn’t completely understood, but studies suggest that this gene creates proteins for several parts of your child’s body, which is why symptoms of Smith-Magenis syndrome are so broad.

A chromosome deletion (a portion containing the RAI1 gene) or a mutation of the RAI1 gene itself causes Smith-Magenis syndrome. Nearly 90% of children diagnosed with the condition are missing the RAI1 gene, which is part of the short arm (p) of chromosome 17 (17q11.2).

The chromosome deletion is spontaneous (de novo) and happens randomly when the egg and sperm meet at conception. In very rare cases, chromosomes from the egg and sperm break apart and trade places with each other (translocation). These rare cases happen very early during the development of an embryo. The remaining 10% of those diagnosed have a genetic mutation of the RAI1 gene, which causes a change in the structure of the child’s DNA at that specific gene location.

Diagnosis

A diagnosis of Smith-Magenis syndrome usually occurs during childhood when symptoms become more apparent. Your child’s provider will ask questions to learn more about their symptoms, take a complete medical history and examine your child. A genetic blood test is necessary to confirm a diagnosis and rule out similar conditions.

Treatment

Treatment for Smith-Magenis syndrome focuses on relieving symptoms of the condition, which could include:

Enrolling your child in early intervention (before age 3) and educational programs (after age 3) to help your child meet developmental and academic milestones.

Encouraging your child’s active participation both at home and in the community.

Participating in outpatient therapies such as speech-language therapy, behavioral therapy, physical therapy and/or occupational therapy.

Taking medications to treat specific symptoms of co-existing conditions such as ADHD or disordered sleep.

Wearing glasses to correct vision problems.

Getting tubes surgically placed in your child’s ears to prevent infections and monitor for hearing loss.

Eating a healthy, well-balanced diet and exercising regularly to manage weight.

Your child’s provider will individualize their treatment to fit your child’s needs to help them thrive.

Type of Doctor Department : Pediatricians/neurologists 

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