CausesBy Mayo Clinic Staff
Most people are born with two sex chromosomes. A boy inherits the X chromosome from his mother and the Y chromosome from his father. A girl inherits one X chromosome from each parent. If a girl has Turner syndrome, one copy of the X chromosome is missing or significantly changed.
The genetic alterations of Turner syndrome may be one of the following:
- Monosomy. The complete absence of an X chromosome generally occurs because of an error in the father's sperm or in the mother's egg. This results in every cell in the body having only one X chromosome.
- Mosaicism. In some cases, an error occurs in cell division during early stages of fetal development. This results in some cells in the body having two complete copies of the X chromosome. Other cells have only one copy of the X chromosome, or they have one complete and one altered copy.
- Y chromosome material. In a small percentage of Turner syndrome cases, some cells have one copy of the X chromosome and other cells have one copy of the X chromosome and some Y chromosome material. These individuals develop biologically as girls, but the presence of Y chromosome material increases the risk of developing a type of cancer called gonadoblastoma.
Effect of the chromosomal errors
The missing or altered X chromosome of Turner syndrome causes errors during fetal development and other developmental problems after birth — short stature, ovarian failure and learning disabilities. Physical characteristics and health complications that arise from the chromosomal error vary greatly.
Aug. 23, 2014
- Turner syndrome. Genetics Home Reference. http://ghr.nlm.nih.gov/condition/turner-syndrome. Accessed July 22, 2014.
- Learning about Turner syndrome. National Human Genome Research Institute. http://www.genome.gov/19519119. Accessed July 22, 2014.
- Turner syndrome. National Organization for Rare Disorders (NORD). https://www.rarediseases.org/rare-disease-information/rare-diseases/byID/112/viewFullReport. Accessed July 22, 2014.
- Turner syndrome. Eunice Kennedy Shriver National Institute of Child Health and Human Development. http://turners.nichd.nih.gov/index.html. Accessed July 22, 2014.
- Saenger P. Clinical manifestations and diagnosis of Turner syndrome (gonadal dysgenesis). http://www.uptodate.com/home. Accessed July 22, 2014.
- Milbrandt T, et al. Turner syndrome. Pediatrics in Review. 2013;34:420.
- Saenger P. Management of Turner syndrome (gonadal dysgenesis). http://www.uptodate.com/home. Accessed July 22, 2014.
- Turner Syndrome Society of the United States. http://www.turnersyndrome.org/. Accessed July 26, 2014.
- Wick MJ (expert opinion). Mayo Clinic, Rochester, Minn. Aug. 1, 2014.
- Hoecker JL (expert opinion). Mayo Clinic, Rochester, Minn. July 27, 2014.
- Freriks K, et al. Long-term effects of previous oxandrolone treatment in adult women with Turner syndrome. European Journal of Endocrinology. 2013;168:91.