The combination of primary ovarian failure with constitutional (that is, genetically determined) shortness; often with other clinical abnormalities, including 'webbing' of the neck; an increased 'carrying angle' at the elbow; short fourth metatarsal (feet) and metacarpal (hand) bones (the bone within the hand that leads to the ring finger), and sometimes abnormalities of the heart and the thyroid gland. Associated with a karyotype that is 45,X (a monosomy, with one sex chromosome missing) or with partial loss ('deletion') of one of a pair of X-chromosomes. The single X-chromosome present can come from the mother or the father -- and, interestingly, it behaves differently: if it comes from the mother the girl is likely to be rather socially disruptive (the way little boys typically are), whereas if the X-chromosome comes from the father her behavior tends to be closer to normal for that of a girl!

An abnormality of the chromosome number due to a loss of one chromosome from a diploid set, resulting in 45 chromosomes instead of 46. The only mosomy compatible with fetal development and continued survival is that of Turner syndrome, the karyotype of which is 45,X (i.e. a monosomy of the sex chromosomes).

A measurement done at transvaginal ultrasound of tissue in the neck of the fetus; if excessive, it implies a substantially increased risk that the fetus is affected by Down syndrome and Turner syndrome.

A chromosome that's either the X-chromosome (a pair confers femaleness in a normal diploid complement of chromosomes) or the Y-chromosome (just one confers maleness in a normal diploid complement of chromosomes); distinct from the non-sex chromosomes, or autosomes (which are numbered from 1 to 22); aneuploidies give rise to Turner syndrome, Klinefelter syndrome, triple-X syndrome, extra-Y-chromosome syndrome) etc; examined in a karyotype.