Product Description:
Chromosomal mosaicism is best detected by conventional cytogenetic studies. In order to determine the ability of microarray testing to detect mosaicism, we performed retrospective analysis among patients with concurrent chromosome analysis and microarray studies. A total of 1590 clinical genetic cases were studied using ISCA 4x44K oligonucleotide microarray as well as high-resolution chromosome analysis. Of these 1590 cases, 22 (1.3%) had an abnormal mosaic chromosome complement. Microarray detected the abnormality in 18/22 cases (81.8%). In 10 cases, the microarray results were clearly suggestive of a mosaic state; in the remaining 8 cases, although the abnormality was identified by microarray, the mosaicism was indistinguishable. Among the 18 cases where an abnormality was detected and a normal cell line was present, the percentage of abnormal cells ranged from 12.5% - 65%. Microarray studies did not detect the mosaic abnormality in four cases (4/22; 18.2%) because of low-level mosaicism ranging from 6.6% - 23% as determined by cytogenetic analysis. Three of these cases were whole chromosome trisomies and one case exhibited a structural abnormality. Although chromosome and/or FISH studies are needed to confirm mosaicism and to determine percentages of abnormal cells, microarray studies accurately define breakpoints involved in structural abnormalities and can delineate the origin of derivative chromosomes for more precise definition of the abnormal karyotype. Our data showed that mosaicism was identified in approximately 1 in every 10 patients referred for concurrent microarray and chromosome analysis and the X chromosome was most frequently involved in mosaic abnormalities. Microarray independently identified mosaicism in at least half of these abnormal mosaic cases. However, as microarray becomes the first tier test, it is important to establish thresholds for detection of chromosomal mosaicism and recognize that a subset of patients may benefit from a reflex chromosome analysis.
