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Introduction

Turner syndrome is a sex chromosome disorder caused by complete or partial loss of an X chromosome.  Patients with Turner syndrome can develop a variety of complications that involve a multitude of organ systems (eg, cardiovascular, reproductive).

Pathophysiology and risk factors

Female individuals who are 46,XX undergo lyonization (random inactivation of one X chromosome in a given cell).  However, certain genes remain active on the otherwise inactive X chromosome.  Therefore, patients with complete or partial loss of an X chromosome only have 1 copy of these genes (ie, Turner syndrome), which affects growth and development.

The partial or complete loss of an X chromosome can result from any of the following:

  • 45,X ( Image 1):  Approximately 50% of patients with Turner syndrome have monosomy X.  Of these patients, two-thirds have a maternally derived X chromosome, and one-third have a paternally derived X chromosome.  Aneuploidy most often occurs due to meiotic nondisjunction (ie, failed separation of homologous chromosomes or sister chromatids) during gametogenesis (

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