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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]
Turner syndrome results from a single X chromosome (45,X or 45,X0). Klinefelter syndrome, the most common male chromosomal disease, otherwise known as 47,XXY, is caused by an extra X chromosome. Edwards syndrome is caused by trisomy (three copies) of chromosome 18. Down syndrome, a common chromosomal disease, is caused by trisomy of chromosome 21.
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.
The following is a list of genetic disorders and if known, type of mutation and for the chromosome involved. Although the parlance "disease-causing gene" is common, it is the occurrence of an abnormality in the parents that causes the impairment to develop within the child.
Exceptions to this finding are extremely rare cases in which boys with Klinefelter syndrome (44+xxy) also inherit an X-linked dominant condition and exhibit symptoms more similar to those of a female in terms of disease severity. The chance of passing on an X-linked dominant disorder differs between men and women.
Harry Fitch Klinefelter Jr. (/ ˈ k l aɪ n f ɛ l t ər /; March 20, 1912 – February 20, 1990) was an American rheumatologist and endocrinologist. Klinefelter syndrome is named after him. Biography
Some X-linked dominant conditions such as Aicardi syndrome are fatal to boys; therefore only girls with these conditions survive, or boys with Klinefelter's syndrome (and hence have more than one X chromosome).
In 1959, five days after Jérôme Lejeune described the trisomy-21 [3] in Down syndrome, basing himself off Marthe Gautier's work, [4] Jacobs and John Strong described an additional X chromosome in male patients (the 47,XXY karyotype) [5] also known as Klinefelter syndrome, as Harry Klinefelter had already diagnosed the symptoms in 1942.