Identifying Smith-Magenis Syndrome

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Q My 14-year-old daughter has moderate mental retardation. As a young child she had trouble gaining weight, but now is actually overweight. She has always had a habit of "picking" her skin and, as a younger child, she was a "headbanger." She still has outbursts of aggressive behavior that typically are worse at school. Conversely, she responds very well to attention and can be very loving, especially with adults. Her other medical problem is a low thyroid level and myopia (nearsightedness).

She has never been diagnosed as having any specific syndrome, though at one point she was thought to have Prader-Willi syndrome; but her blood test for that was negative.

Recently, a friend of mine who is a nurse at a genetics clinic in a different city mentioned Smith-Magenis syndrome as a possible diagnosis for my daughter. My family doctor has not heard about it. Is this a possibility? Can the diagnosis only be made by a blood test?

A Smith-Magenis syndrome (SMS) is a relatively rare chromosomal disorder (estimated incidence: one out of 25,000 births) caused by a deletion (a missing piece) in chromosome 17. SMS is probably underdiagnosed due to a lack of awareness about it.

Individuals with SMS have some common physical features. These include a prominent forehead, wide jaw with receding chin, wide-set eyes, and a broad, flattened nasal bridge. Short, wide fingers and toes (brachydactyly) and short stature are also typical. Hypotonia (floppy muscle tone) and failure-to-thrive are common in infancy. The degree of mental retardation varies, with most individuals falling into the moderately mentally retarded range. Difficulty sleeping, strabismus (crossed eyes), myopia (nearsightedness) and hearing problems are common. Self-injurious behavior including headbanging, picking at or biting the skin and inserting foreign objects into body orifices are also very common characteristics. Low thyroxine (a thyroid hormone, also, known as T4) occurs in approximately 30 percent of cases. Other less common abnormalities occur in the heart, brain and kidneys. Children with SMS have engaging. personalities, are very communicative and love attention.

Interestingly, one patient in my practice was suspected of having Prader-Willi syndrome, but the diagnosis was not confirmed with chromosome testing (see comments below). She subsequently was diagnosed with SMS using fluorescence in situ hybridization (FISH) analysis.

It is impossible for me to say for sure, but based on your description of your daughter's symptoms and behavior, I would definitely recommend further evaluation by a genetics specialist. Perhaps, if the clinic your friend works at is not too far, you might take your daughter there.

The diagnosis of SMS can be made by experienced clinicians, typically genetic specialists, in individuals order than 20, based on the distinctive phenotype (appearance) of SMS. …