CRITICAL ELEMENTS OF GENETIC EVALUATION AND GENETIC COUNSELING
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Pseudomosaicism |
Date: 5/2/97* |
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Disclaimer The "Critical Element of Genetic Evaluation and Genetic Counseling" was written and approved by genetic professionals and perinatologists within the state of Washington. The document is to act as an aid to medical geneticists, genetic counselors, and perinatologists who practice within our state. This Critical Element of Genetic Evaluation and Genetic Counseling does not define the applicable standard of care, nor is it intended to dictate an exclusive course for the diagnosis, counseling, treatment or management of genetic conditions or birth defects. The authors acknowledge that appropriate clinical practices may vary depending upon a number of factors including, among others, the needs and choices of the individual patient, the resources available, and limitations unique to the particular institution or type of practice.
True mosaicism may have clinical significance for a fetus and therefore, should be reported out to the patient (see separate critical element) Amnio pseudomosaicism in amniotic fluid samples: Pseudomosaicism is an artifact occurring in tissue culture in approximately 2-3% nationally of all amniotic fluid samples. It refers to the finding of:
or
There are specified cytogenetic protocols for extended analysis depending on the chromosome involved, and if the abnormality is observed in a clone or in mass culture, to determine that the chromosome abnormality is an in vitro event resulting in pseudomosaicism (see Hsu, L. Prenatal Diagnosis, vol 12:555-573, 1992) If pseudomosaicism is concluded: Since it is, by definition, an in vitro event, there would not be a risk for a phenotypic effect. It is not customary to report pseudomosaicism to the patient. If included in the lab report, reporting to the patient is left to the discretion of the clinician. CVS pseudomosaicism in chorionic tissue: Until more data is accumulated, clear guidelines for genetic counseling regarding CVS mosaicism vs. pseudomosaicism cannot be well defined. A follow-up ultrasound and amniocentesis should be offered to the patient to help clarify this issue. * This Critical Element of Genetic Evaluation and Genetic Counseling was unanimously approved at a state genetics practitioners meeting on 5/02/96.
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