Smith Magenis syndrome is due to a mutation of the RAI 1 gene on chromosome 17 in the fetus affecting 1 in 25,000 births.
It results in multi organ abnormalities. People affected with this syndrome have problems with speech development and language skills. They suffer from mild to moderate mental retardation, behavior disturbances and sleep disorders. Here is an image of a mother and her child with the syndrome.
Signs and symptoms
There is a square face with deep-set eyes. The chin is prominent, the bridge of the nose flattened. The mouth tends to be turning downwards. These facial features often develop only later in life. People with Smith Magenis syndrome have problems falling asleep and tend to wake up several times per night, so they often are very sleepy during the day. Although they have affectionate personalities, they also suffer from impulsiveness, temper tantrums and anger outbursts. They engage in self-injurious practices such as head banging, skin picking, hitting and biting. They tend to lick their fingers and compulsively turn pages in books or magazines (“lick and flip” behavior). Small stature and scoliosis (spinal curvature) is common. Short-sightedness (myopia) is frequently noticed. They can also have ear deformities and hearing loss. Heart and kidney deformities are also common.
Chromosomal analysis on cultured lymphocytes shows the deletion on the short arm of chromosome 17 using the fluorescence in situ hybridization (FISH) with DNA probes specific for the 17p11.2 gene location.
Depending on how severe the mental retardation is and what life threatening heart or kidney abnormalities are present, the individuals may have a higher mortality in the earlier years. The ones who survive longer usually have less abnormalities and may have less severe mental retardation, the degree of which will determine whether they will to be placed in a care home or not.
2. McPherson & Pincus: Henry’s Clinical Diagnosis and Management by Laboratory Methods, 21st ed., Copyright © 2006 W. B. Saunders Company: Prenatal Cytogenetics