Trisomy 13 or the Patau syndrome is a genetic disorder in which the person suffering from it has 3 copies of genetic material of chromosome 13. It occurs in about 1 out of 10,000 newly born babies.

It occurs when the extra DNA of chromosome 13 emerges in all or some of the cells in the body. While Trisomy 13 mosaicism is caused by the presence of extra chromosome 13 in the cells, partial Trisomy 13 occurs because of the presence of a part of the extra chromosome in cells.