Most people have 46 chromosomes in each of their cells, and two of those 46 chromosomes are sex chromosomes. Most girls and women have two X sex chromosomes (so we say their chromosomal component is “46,XX”). Most boys and men have an X sex chromosome and a Y sex chromosome (“46,XY”).
But some people have “mosaic” chromosomes, meaning that not all their cells have the same component of chromosomes. This is called “mosaicism” because it is sort of like the body is made up of a varied set of colored tiles, rather than a single-colored set of tiles. When a person has more than one component of sex chromosomes, the person is said to have “sex chromosome mosaicism.”
So, some people have 46,XX in some cells with 46,XY in other cells. Some may have 46,XY in some cells and 47,XXY in other cells. Some may have 45,X in some cells and 46,XX in others. Many other variations are possible.
A common misperception is that all forms of DSD involve sex chromosome mosaicism. In fact, only a few forms of DSD appear to involve sex chromosome mosaicism.
Posted in: Specific Conditions