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Klinefelter syndrome is not an inherited condition. The extra X chromosome comes from the mother in approximately 50% of the cases. Maternal age is the only known risk factor. Women at 40 years have a four-times-higher risk of a child with Klinefelter syndrome than women aged 24 years. [14] [34] [35]
Klinefelter syndrome is the most common sex chromosome aneuploidy in humans. It represents the most frequent cause of hypogonadism and infertility in men. Most cases are caused by nondisjunction errors in paternal meiosis I. [2] About eighty percent of individuals with this syndrome have one extra X chromosome resulting in the karyotype XXY ...
Hypergonadotropic hypogonadism can be caused by a variety of genetic and acquired factors. Common genetic causes include Turner syndrome and Klinefelter syndrome, while acquired causes may involve infections, trauma, radiation, or chemotherapy affecting the gonads. [13]
This includes patients with Turner Syndrome (45,X or 45,X0) and Klinefelter Syndrome (47,XXY) even though they do not generally present with atypical genitals. XX, Sex reversal: consist of two groups of patients with male phenotypes, the first with translocated Sex-determining region Y protein (SRY) and the second with no SRY gene.
Klinefelter syndrome is an example of human polysomy X with the karyotype 47, XXY. X chromosome polysomies can be inherited from either a single maternal (49, X polysomies) or paternal (48, X polysomies) X chromosome. [18] Polysomy of sex chromosomes is caused by successive nondisjunctions in meiosis I and II. [6]
Sex chromosome anomalies belong to a group of genetic conditions that are caused or affected by the loss, damage or addition of one or both sex chromosomes (also called gonosomes). In humans this may refer to: 45, X, also known as Turner syndrome; 45,X/46,XY mosaicism, also known as X0/XY mosaicism and mixed gonadal dysgenesis; 46, XX/XY
An example of this is one of the milder forms of Klinefelter syndrome, called 46,XY/47,XXY mosaic wherein some of the patient's cells contain XY chromosomes, and some contain XXY chromosomes. The 46/47 annotation indicates that the XY cells have the normal number of 46 total chromosomes, and the XXY cells have a total of 47 chromosomes.
Increased levels of these hormones will cause the body to not start puberty, not undergo menarche, and not develop secondary sex characteristics. [9] [10] If ovarian tissue is present and produces some amount of hormones, limited menstrual cycles can occur. [9] 46,XX gonadal dysgenesis can manifest from a variety of causes. [6]