Turner mosaicism

The answer is d. (Murray, pp 812—828. Scriver, pp 3-45. Sack, pp 57-84. Wilson, pp 123—148.) The case described represents one of the more common chromosomal causes of reproductive failure. Turner mosaicism. Turner s syndrome represents a pattern of anomalies including short stature, heart defects, and infertility. Turner s syndrome is often associated with a 45,X karyotype (monosomy X) in females, but mosaicism (i.e., two or more cell lines with different karyotypes in the same individual) is common. However, chimerism (i.e., two cell lines in an individual arising from different zygotes, such as fraternal twins who do not separate) is extremely rare. Trisomy refers to three copies of one chromosome, euploidy to a normal chromosome number, and monoploidy to one set of chromosomes (haploidy in humans). 

Detection of chromosome fragments. Individuals with Turner s syndrome are, in some cases, mosaic for a portion of or for the entire Y chromosome (46,XY/45,X). Since such individuals may be at increased risk for gonadal tumors, Southern blot or PCR analysis has been used to detect the presence of Y chromosome segments in studies of DNA from peripheral blood samples. Similarly, the fetal sex as well as the presence of some aneuploid states (e.g., trisomy 18) can be determined by analysis of DNA from chorionic villi or amniotic fluid cells. 

Up to 25% of patients with Turner syndrome exhibit a mosaic karyotype, in which only some cells have the 45,X karyotype classically associated with the condition. 

Since Turner s syndrome results from the absence of the Y chromosome (see Fig. 8-25), it may be relevant that XO mice have been produced by irradiating mice immediately after fertilization, which suggests that the Y chromosome is extremely sensitive to radiation at this time. When dysfunction occurs after fertilization, such mosaicisms as XX/XO and XXX/XO have been observed. Such karyotypes may be associated with the clinical manifestations of Turner s syndrome. 

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