© 2017, GENASSIST, Inc.     

By Keith S. Wexler, MBA, Maternal Fetal Medicine, Prenatal Diagnosis and Biotech /Life Sciences Consultant, GENASSIST, Inc.

Paul Wexler, M.D., F.A.C.O.G., Medical Director, GENASSIST, Inc.

Clinical Professor, Department of OB/GYN, University of Colorado Health Sciences Center

Clinical Professor, Division of Genetics/Dept. of Pediatrics, Univ. of Colorado/The Children’s Hospital

Background: The breakdown of fetal cells in the maternal circulation make it possible for laboratories to screen for Fetal DNA in pregnancy.

Maternal Fetal Circulating Cell Free DNA (cf DNA) has helped uncover microdeletions – losses of very small pieces of chromosome(s) that are not visible under a microscope and can be associated with syndromes in a child.

Prior to Maternal Fetal DNA screening tests in pregnancy, the only way that a patient would know if they had a child with a microdeletion was at delivery with an “affected” child.

Prader-Willi Syndrome: Is characterized by developmental delay and weak muscle tone. A compulsive eating disorder which can lead to obesity can develop later. This syndrome is caused by a deletion of a small portion of the long arm of chromosome #15 (15q11-13) or Maternal Isodisomy (both copies of chromosome #15 is inherited from the mother).

  • Incidence – 1 in 10,000 births.


At the current time the value of “routine” screening for Microdeletions on all patients is controversial because of the low prevalence of these disorders and the possibility of “false positive” and “false negative” results.

However, when a patient is identified as a candidate for invasive testing i.e. Chorionic Villus Sampling (CVS) and/or amniocentesis, the addition of Microdeletions may be indicated, particularly if family history or ultrasound findings suggest an increased possibility for detection of one of these rare disorders.