Prenatal Diagnosis of Smith-Magenis Syndrome (del 17p11.2)

Smith-Magenis syndrome is associated with a microdeletion of the short arm of chromosome 17 with phenotypic abnormalities including dysmorphic facies, self-injurious behavior, mental and neurologic disturbances, and congenital cardiac defects. The majority of patients present in mid-childhood or adulthood. We describe a fetus in which the diagnosis of Smith-Magenis syndrome was made at 16 weeks of gestation following amniocentesis for increased risk for Down syndrome detected by second-trimester maternal serum screening. Ultrasound evaluation revealed multiple fetal anomalies. The pregnancy was terminated at 20 weeks of gestation. Post-mortem findings included dysmorphic facial features, tetralogy of Fallot, a thymic duct remnant, pancreatic islet cell hyperplasia, and abnormal lung fissuring. This represents the second case of prenatally diagnosed Smith-Magenis syndrome. Molecular genetic techniques in the diagnosis of the Smith-Magenis syndrome and other small deletions are becoming an important tool in the genetic evaluation of ultrasound abnormalities.