Turner syndrome (TS) results from the absence of some or all of the X chromosome, with a karyotype of 45,X in the fully developed syndrome. Because not all genes on the X chromosome are inactivated normally, the diminished expression of these genes presumably leads to the TS phenotype, including short stature, incomplete sexual development and reproductive function, and other structural and cognitive abnormalities. Research has begun to identify genes that are potentially linked to TS, including the short stature homeobox (SHOX) gene and DFRX, the human homolog of a fruitfly gene involved in oogenesis.