Pentasomy X is a sex chromosome anomaly caused by the presence of three extra X chromosomes in females (49,XXXXX instead of 46,XX). The disease is pentasomy X (MONDO_0015228). Also known as: 49, XXXXX syndrome, 49,XXXXX syndrome, Penta X Syndrome, Pentasomy type X, XXXXX syndrome, penta X syndrome, penta-X, poly-X.