Turner syndrome

[Little_Girl]

Turner syndrome is a sex chromosome abnormality in which girls are born with one of their two X chromosomes partially or completely missing.

Turner syndrome is caused by the deletion of part or all of one of the two X chromosomes.
Girls with the syndrome are typically short and with loose skin on the back of the neck, learning disabilities, and an inability to undergo puberty.
The diagnosis is confirmed by analyzing the chromosomes.
Treatment with hormones can stimulate growth and initiate puberty.

Chromosomes are structures within cells that contain DNA and many genes. A gene is a segment of deoxyribonucleic acid (DNA) and contains the code for a specific protein that functions in one or more types of cells in the body (see Genes and Chromosomes for a discussion about genetics). Genes contain instructions that determine how the body is supposed to function.
The sex chromosomes determine whether a fetus becomes male or female. A pair of X and Y chromosomes (XY) results in a male, and a pair of X and X chromosomes (XX) results in a female.
Turner syndrome occurs in about 1 out of 2,500 live female births. However, this chromosome abnormality is much more common at conception, but 99% of affected fetuses abort spontaneously.

[Dianne]

In Turner syndrome, girls are born with one of their two X chromosomes partly or completely missing. Diagnosis is based on clinical findings and is confirmed by cytogenetic analysis. Treatment depends on manifestations and may include surgery for cardiac anomalies and often growth hormone therapy for short stature and estrogen replacement for pubertal failure.
(See also Overview of Chromosomal Anomalies and see Overview of Sex Chromosome Anomalies.)
Turner syndrome occurs in about 1/2500 live female births worldwide. However, 99% of 45,X conceptions abort spontaneously.
About 50% of affected girls have a 45,X karyotype; about 80% have lost the paternal X. Most of the other 50% have mosaicism (eg, 45,X/46,XX or 45,X/47,XXX). Among mosaic girls, phenotype may vary from that of typical Turner syndrome to normal. Occasionally, affected girls have one normal X and one X that has formed a ring chromosome. Some affected girls have one normal X and one long-arm isochromosome formed by the loss of short arms and development of a chromosome consisting of two long arms of the X chromosome. These girls tend to have many of the phenotypic features of Turner syndrome; thus, deletion of the X chromosome’s short arm seems to play an important role in producing the typical phenotype.