Turner syndrome is a genetic condition that affects females and results from a complete or partial absence of one of the two X chromosomes. The genotypic and phenotypic features of Turner syndrome are as follows:
Genotypic Features:
- Monosomy X (45,X): The most common chromosomal abnormality in Turner syndrome involves a missing X chromosome in all or some of the cells. This can result in a complete absence of one of the X chromosomes, leaving females with a 45,X genotype.
- Partial X-chromosome abnormalities: In some cases, Turner syndrome is caused by partial deletion or structural abnormalities of one of the X chromosomes (e.g., isochromosome X or ring chromosome X).
- Mosaic Turner syndrome (45,X/46,XX or 45,X/47,XXX): Some individuals have a mosaic pattern where some cells have a typical 46,XX complement while others are 45,X. This can result in milder phenotypic features.
Phenotypic Features:
- Short stature: Most individuals with Turner syndrome are shorter than average due to early cessation of growth and a lack of estrogen production.
- Delayed puberty: Estrogen deficiency leads to delayed secondary sexual characteristics, such as breast development, and the absence or incomplete onset of menstruation.
- Webbed neck: A physical feature common in Turner syndrome is a short, webbed neck.
- Low hairline: Some individuals may have a low posterior hairline.
- Broad chest with widely spaced nipples: This is a typical feature due to abnormal development of the chest.
- Cardiovascular anomalies: Structural heart defects like coarctation of the aorta or bicuspid aortic valve are common.
- Renal anomalies: Kidney issues such as horseshoe kidney or kidney malformations can occur.
- Ovarian failure: The ovaries are often underdeveloped, leading to infertility due to premature ovarian failure.
- Normal intelligence: Although cognitive development is usually normal, there can be some areas where learning difficulties may occur, particularly with mathematics and spatial skills.