X chromosome microarray result on patient 3. The primary result from top to bottom is two copies of the X chromosome in ~120 Mb of the X chromosome in ~85–90% of the cells and one copy of the X chromosome [45,X] in ~18% of the cells (lower triangle). One extra copy of the X chromosome region [46,X,dup(X)(q21.1q21.3)] in ~82% of cells (upper triangle). FISH with a duplicated region confirmed that the cells with a single X chromosome contained only the normal X and each X chromosome had a single XIST gene in band Xq13. The horizontal axis is drawn and the result plotted as the natural logarithm of the data to ensure quantification of multiple copies in the same cell occasionally seen as amplified copies. The image is provided by Daniel Pineda-Alvarez M.D., FACMG, Associate Microarray Director, GeneDx. The difference in the GTW banded chromosome breakpoints is based upon lower resolution FISH analysis using a limited number of chromosome probes and measuring the distance on idiograms that are not based upon measured band location.