Turner Syndrome
Turner syndrome (TS) is one of the most common human chromosome anomalies. It occurs in approximately 1:2,000 female live births regardless of ethnic background. Girls with TS have an abnormal or missing X chromosome that causes short stature and may caus
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Turner Syndrome Marsha L. Davenport, Judith Ross, and Phillippe F. Backeljauw
Abstract
Turner syndrome (TS) is one of the most common human chromosome anomalies. It occurs in approximately 1:2,000 female live births regardless of ethnic background. Girls with TS have an abnormal or missing X chromosome that causes short stature and may cause lymphedema, cardiac abnormalities, gonadal dysgenesis, dysmorphic features, nonverbal learning disabilities, and other problems. Keywords
Gonadal dysgenesis • Growth failure • Sex chromosome abnormalities • X chromosome • Growth hormone • Ovarian failure
M.L. Davenport, M.D. (*) Division of Pediatric Endocrinology, University of North Carolina, 3341 MBRB, CB #7039, 111 Mason Farm Road, Chapel Hill, NC 27599-7039, USA e-mail: [email protected] J. Ross, M.D. Division of Pediatric Endocrinology, Department of Pediatrics, Thomas Jefferson University, Philadelphia, PA, USA P.F. Backeljauw, M.D. Department of Endocrinology, Cincinnati Children’s Hospital, Cincinnati, OH, USA S. Radovick and M.H. MacGillivray (eds.), Pediatric Endocrinology: A Practical Clinical Guide, Second Edition, Contemporary Endocrinology, DOI 10.1007/978-1-60761-395-4_7, © Springer Science+Business Media New York 2013
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Introduction Turner syndrome (TS) is one of the most common human chromosome anomalies. It occurs in approximately 1:2,000 female live births [1] regardless of ethnic background. Girls with TS have an abnormal or missing X chromosome that causes short stature and may cause lymphedema, cardiac abnormalities, gonadal dysgenesis, dysmorphic features, nonverbal learning disabilities, and other problems [2, 3].
Pathogenesis Approximately 50–60% of girls with TS are reported to have a 45,X karyotype. The loss of one X chromosome usually occurs as a result of a nondisjunction error during paternal meiosis since the single X chromosome in 60–80% of girls with TS is maternal in origin. Advanced maternal age may increase these errors [4]. These girls tend to have the most severe phenotype and are frequently diagnosed as newborns [5, 6]. 20–30% have structural abnormalities of the X chromosome such as rings, isochromosomes of the long arm, and partial deletions of the short arm. Thirty to 40% have mosaic patterns (karyotypes having two or more distinct cell types) involving the X chromosome such as 45,X/46,XX, 45,X/46,X,i(X), and 45,X/46,XY. This is thought to result from chromosome loss after fertilization [7] In normal 46,XX females, either the maternal or paternal X chromosome is randomly inactivated in somatic cells during the late blastocyst stage and all descendants of that cell have the same inactive X. However, many genes escape inactivation [8]. In fact, about 15% of genes are expressed from both X chromosomes regularly and another 10% of the genes do so variably [9]. Many of the genes that remain active are located at the tip of the X chromosome and have homologous genes on the Y chromosome. These “pseudoautosomal” regions (PAR) are the only ones in
M.L. Davenport et al.
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