The Association for X and Y Chromosome Variations (AXYS) is dedicated to addressing the needs of those affected by one or more extra X and/or Y chromosomes. We are focused on sharing knowledge, offering support, and initiating action to help improve lives of individuals and families. Trisomy X. 47,XXY, also known as Klinefelter syndrome. 47,XYY, occasionally referred to as Jacob’s syndrome. . 48,XXXX, 48XXXY, 48XXYY and 48XYYY; 49XXXXX, 49XXXXY, 49XXXYY, 49XXYYY and 49XYYY. Some individuals may have two cell lines, which is called mosaicism, such as 46,XY/47,XXY.