A 25-year-old woman with amenorrhea has never had menarche. On physical examination, she is 145 cm (4 ft 9 in) tall. She has a webbed neck, a broad chest, and widely spaced nipples. Strong pulses are palpable in the upper extremities, but there are only weak pulses in the lower extremities. On abdominal MR imaging, her ovaries are small, elongated, and tubular. Which of the following karyotypes is she most likely to have?

The features described are those of classic Turner syndrome. Individuals who reach adulthood may have mosaic cell lines, with some 45, X cells and some 46, XX cells. A female carrier of the fragile X syndrome, X(fra), is less likely to manifest the disease than a male, but the number of triple repeat sequences (CGG) increases in her male offspring. The 47, XXY karyotype occurs in Klinefelter syndrome; affected individuals appear as phenotypic males. The "superfemale" karyotype (XXX) leads to mild mental retardation. Trisomy 16 is a cause of fetal loss early in pregnancy.