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.