Abstract
The past decade produced important advances in molecular genetic techniques potentially supplanting the traditional cytogenetic diagnosis of Turner syndrome (TS). Rapidly evolving genomic technology is used to screen 1st trimester pregnancies for sex chromosomal anomalies including TS, and genomic approaches are suggested for the postnatal diagnosis of TS. Understanding the interpretation and limitations of new molecular tests is essential for clinicians to provide effective counseling to parents or patients impacted by these tests. Recent studies have advanced the concept that X chromosome genomic imprinting influences expression of the Turner phenotype and contributes to gender differences in brain size and coronary disease. Progress in cardiovascular MRI over the past decade has dramatically changed our view of the scope and criticality of congenital heart disease in TS. Cardiac MRI is far more effective than transthoracic echocardiography in detecting aortic valve abnormalities, descending aortic aneurysm, and partial anomalous pulmonary venous return; recent technical advances allow adequate imaging in girls as young as seven without breath holding or sedation. Finally, important developments in the area of gynecological management of girls and young women with TS are reviewed, including prognostic factors that predict spontaneous puberty and potential fertility and recent practice guidelines aimed at reducing cardiovascular risk for oocyte donation pregnancies in TS.
Highlights
Clinical consensus defines Turner syndrome (TS) as a genetic disorder due to “complete or partial” X chromosome monosomy, with short stature the most constant feature, and variable expressivity of ovarian, cardiovascular, and renal defects [1]
Some authors do not believe that complete X monosomy is compatible with survival and postulate the existence of a normal cell line that rescues the embryo during early gestation [2]
If a sex chromosome is lost very early in embryo development, at least half of cells would retain a normal or trisomic sex chromosome complement, and it seems quite unlikely that the healthy cell line would die out while the abnormal 45,X cells take over during fetal development
Summary
Clinical consensus defines Turner syndrome (TS) as a genetic disorder due to “complete or partial” X chromosome monosomy, with short stature the most constant feature, and variable expressivity of ovarian, cardiovascular, and renal defects [1]. With progress in genotype-phenotype research in humans and mice, it has become very clear that penetrance and expressivity of specific gene deletions is highly dependent on the individual genetic “background” and environmental factors It seems that X monosomy need not always be lethal, and the survival and relatively healthy development of some 45,X girls are more likely related to variation in. The abnormal fragmentary sex chromosome is frequently lost during mitotic cell divisions in the course of postzygotic development, resulting in mosaicism for the original cell with fragmentary sex chromosome and a pure monosomic cell line, for example, 46,X,isoXq/45,X This type of mosaicism does not ameliorate the phenotype since all cells have monosomy for the X chromosome short arm (Xp). Normal adult women undergoing investigation of infertility may be found to have deletion of terminal portions of an Xq (long arm) without other features of TS and they should not be classified with TS
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