The phenotype of a pig with monosomy X resembling Turner syndrome symptoms: a case report

The Hypothesis of the Prolonged Cell Cycle in Turner Syndrome

Turner syndrome (TS) is a chromosomal disorder that is caused by a missing or structurally abnormal second sex chromosome. Subjects with TS are at an increased risk of developing intrauterine growth retardation, low birth weight, short stature, congenital heart diseases, infertility, obesity, dyslipidemia, hypertension, insulin resistance, type 2 diabetes mellitus, metabolic syndrome, and cardiovascular diseases (stroke and myocardial infarction). The underlying pathogenetic mechanism of TS is unknown. The assumption that X chromosome-linked gene haploinsufficiency is associated with the TS phenotype is questioned since such genes have not been identified. Thus, other pathogenic mechanisms have been suggested to explain this phenotype. Morphogenesis encompasses a series of events that includes cell division, the production of migratory precursors and their progeny, differentiation, programmed cell death, and integration into organs and systems. The precise control of the growth and differentiation of cells is essential for normal development. The cell cycle frequency and the number of proliferating cells are essential in cell growth. 45,X cells have a failure to proliferate at a normal rate, leading to a decreased cell number in a given tissue during organogenesis. A convergence of data indicates an association between a prolonged cell cycle and the phenotypical features in Turner syndrome. This review aims to examine old and new findings concerning the relationship between a prolonged cell cycle and TS phenotype. These studies reveal a diversity of phenotypic features in TS that could be explained by reduced cell proliferation. The implications of this hypothesis for our understanding of the TS phenotype and its pathogenesis are discussed. It is not surprising that 45,X monosomy leads to cellular growth pathway dysregulation with profound deleterious effects on both embryonic and later stages of development. The prolonged cell cycle could represent the beginning of the pathogenesis of TS, leading to a series of phenotypic consequences in embryonic/fetal, neonatal, pediatric, adolescence, and adulthood life.

Application of droplet digital PCR in diagnosing of X monosomy in mares

BACKGROUND

X monosomy is the most common disorder of sex development in horses. Although cytogenetic analysis is still the gold standard in the diagnosis of equine X monosomy, novel molecular techniques are being sought to quickly and reliably detect this chromosome abnormality.

OBJECTIVES

The goal of this study was to evaluate the usefulness of a novel variant of the PCR technique-namely, droplet digital PCR (ddPCR)-in the detection of X monosomy in mares.

STUDY DESIGN

A proof of concept of the usefulness of ddPCR in diagnosing an abnormal number of X chromosomes in mares.

METHODS

We examined an infertile mare using cytogenetic (fluorescent in situ hybridisation-FISH) and molecular (droplet digital PCR-ddPCR) techniques. The X chromosome copy number in ddPCR was estimated via detection of the AMELX gene copy number. In addition, 70 mares homozygous for X-linked microsatellite marker (LEX3) were examined by ddPCR. For all mares, a PCR search for the Y-linked SRY gene was also performed.

RESULTS

Cytogenetic analysis and ddPCR gave concordant results, indicating pure X monosomy in the studied mare. Of the 70 additional mares examined by ddPCR, a single copy of the X chromosome was found in two cases. All mares were SRY-negative and thus both freemartinism, manifested by leucocyte XX/XY chimerism, and sex reversal syndrome (XX, SRY-positive) could be excluded.

MAIN LIMITATIONS

The ddPCR approach does not allow for unequivocal identification of mosaicism (63,X/64,XX or 65,XXX/64,XX), but may give an indication that further cytogenetic analysis is necessary.

CONCLUSION

The ddPCR approach appeared to be useful for diagnosing nonmosaic X monosomy in mares. If the number of X chromosome copies in a mare, as determined by ddPCR, differs from two (in our study, <1.8 or >2.2), additional cytogenetic investigation is recommended with the aim of detecting the mosaicism.