CHROMOSOMAL MOSAICISM AND UNIPARENTAL DISOMY IN PRENATAL DIAGNOSIS: CLINICAL IMPLICATIONS FOR GENETIC COUNSELING

摘要

Prenatally detected chromosomal mosaicism complicates genetic counseling as there is variability in phenotypic outcome and available information pertaining to phenotypic consequences is limited. The objective of this study was to identify the phenotypic effects of mosaicism that was diagnosed prenatally. A total of 4,599 CVS specimens and 15,688 amniocentesis specimens were collected between 1991 and 2005 and clinical information was reviewed for all mosaic cases. Of those procedures, 76 CVS specimens (1.65%) and 66 amniocentesis specimens (0.42%) indicated a mosaic result. However, seven of the mosaic amniocentesis results were observed after a previous mosaic CVS result. When these specimens were removed from the calculation, the incidence of mosaic amniocenteses was 0.38%. Of the cases that had follow-up cytogenetic testing, CVS cases were found to have a true mosaicism rate of 23.6% while amniocentesis cases had a rate of 60.7%. The rates of prenatally detected mosaicism and true fetal mosaicism for Magee-Womens Hospital are comparable to the rates reported in literature. This study found mosaic results involving trisomy for chromosomes 2, 7, 8, 9, 10, 12, 13, 15, 16, 18, 20, 21, 22, X, and Y. In addition, there was monosomy for chromosomes 21, 22, and X, tetraploidy, structural aberrations, and supernumerary marker chromosomes. However, no cases of UPD were identified. From this information, associations were made between the phenotypic outcomes observed in this study and those reported from previous studies. Based on the information provided from this study, it is apparent that phenotype can vary, even when the same abnormality is involved and that more information is needed regarding long term consequences of prenatally diagnosed mosaicism. The results of this study are important to public health because it provides additional data regarding the phenotypic results after prenatal diagnosis of mosaicism for various chromosome abnormalities and increases the understanding of the role of mosaicism in prenatal diagnosis, enabling more effective patient counseling.