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.About 15% of patients in clinical series have mosaicism for 46, XX and/or 47, XXX cell lines in addition to 45, X cell line.Tags: Essay On Imagery In Romeo And JulietEssay On Why I Want To Be A CheerleaderEssay About Word IonMinimally Invasive Percutaneous Plate OsteosynthesisBelonging Creative Writing QuestionsThe Art Of War EssaysOnline Coursework Submission Essex UniversityEssay On German CultureAssign Macro To Command Button
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 .
This view suggests that most if not all surviving apparently 45, X girls arose via loss of the 2nd sex chromosome during early mitotic cell divisions in preimplantation embryos .
National Institute of Child Health and Human Development, National Institutes of Health, CRC 1-3330, 10 Center Dr, NIH, Bethesda, MD 20892, USAReceived ; Accepted 9 September 2014; Published 16 November 2014Academic Editor: Klaus Brusgaard Copyright © 2014 Carolyn Bondy.
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This type of mosaicism does not ameliorate the phenotype since all cells have monosomy for the X chromosome short arm (Xp).
The major phenotypic features of TS such as short stature, congenital cardiovascular defects, and neurocognitive differences are linked to deletion of X or Y chromosome short arms [9–11].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.This genomic technology represented a transition from classic cytogenetics through FISH to artificial chromosomes immobilized on arrays as shown here.Figure 1: Xp deletion in a patient with BAV and aortic coarctation.This class of chromosomal defect usually arises from errors in meiotic recombination.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,iso Xq/45, X.We recently showed that the locus for congenital heart defects in TS map telomeric to cytological band Xp11.4 and Chr X:41,500 000 .This breakpoint was established by array-based comparative genomic hybridization (a CGH) as shown in Figure 1.This hypothetical scenario seems unlikely for several reasons.Firstly, available research on human gametes and embryos indicates that aneuploidy and chromosomal fragmentation commonly occur during meiosis, related to errors of homologous recombination [3, 4].