Isodicentric X chromosome and mosaicism: report on two cases of 45,X/46,X,idic(Xq)/47,X,idic(Xq),idic(Xq) and review of the literature

Double Isochromosome X, a Rare Cytogenetic Variant of Turner Syndrome: A Case Report and a Review of the Literature

Turner Syndrome (TS) is a genetic disorder caused by total or partial loss of an X chromosome. The isochromosome X (i(X)) is a known variant of TS, however, double i(X) is a very rare variant, reported very few times in the literature. We report on a rare case of TS with double i(X). This is an 11-year-old female patient , addressed to the medical genetics consultation for short stature and facial features suggestive of TS. We performed a constitutional postnatal karyotype from a peripheral blood sample, with lymphocyte culture, and an R band analysis, performed on 70 metaphases. Metaphases analysis in our patient identified the presence of three cell populations: 45,X[22]/46,X,i(X)(q10)[30]/47,X,i(X)(q10),i(X)(q10) [18]. The first has total chromosome X monosomy, the second with a normal X chromosome and one isochromosome of the long arm of the other X chromosome and the third with a normal X chromosome and two isochromosomes of the long arm of the X chromosome. A control cell culture was performed from a second blood sample of the patient and confirmed the abnormality. This paper will discuss this case in comparison with other rare cases described, as well as the formation of the double isochromosome, based on the literature.

Cytogenetic Studies in Primary Amenorrhoea Cases

Background:

Amenorrhoea is considered a kind of menstrual disorder in a woman of reproductive age. It is a symptom with many potential causes such as an abnormality in the hypothalamic–pituitary–ovarian axis, anatomical abnormalities of the genital tract or functional causes.

Aims:

In this study, we aimed to investigate chromosomal abnormalities in patients presenting with primary amenorrhoea.

Study Setting and Design:

This study was conducted in the medical genetic laboratory.

Materials and Methods:

Chromosomal analysis was carried out in 134 cases that were referred to the human genetic laboratory from 2010 to 2017, employing (GTG) Giemsa banding.

Statistical Analysis:

Statistical analyses were carried out by Microsoft Office Excel (2019).

Results:

The karyotype results revealed 77.6% (n = 104) with normal chromosome composition while 22.38% (n = 30) showed chromosomal abnormalities. Among the patients with abnormal chromosome constituents, 53.54% exhibited numerical aberration and 46.66% showed structural abnormalities.

Conclusion:

The present study has emphasised that karyotyping is one of the fundamental investigations in the evaluation of primary amenorrhoea.

Large inverted repeats within Xp11.2 are present at the breakpoints of isodicentric X chromosomes in Turner syndrome

Turner syndrome (TS) results from whole or partial monosomy X and is mediated by haploinsufficiency of genes that normally escape X-inactivation. Although a 45,X karyotype is observed in half of all TS cases, the most frequent variant TS karyotype includes the isodicentric X chromosome alone [46,X,idic(X)(p11)] or as a mosaic [46,X,idic(X)(p11)/45,X]. Given the mechanism of idic(X)(p11) rearrangement is poorly understood and breakpoint sequence information is unknown, this study sought to investigate the molecular mechanism of idic(X)(p11) formation by determining their precise breakpoint intervals. Karyotype analysis and fluorescence in situ hybridization mapping of eight idic(X)(p11) cell lines and three unbalanced Xp11.2 translocation lines identified the majority of breakpoints within a 5 Mb region, from approximately 53 to 58 Mb, in Xp11.1-p11.22, clustering into four regions. To further refine the breakpoints, a high-resolution oligonucleotide microarray (average of approximately 350 bp) was designed and array-based comparative genomic hybridization (aCGH) was performed on all 11 idic(X)(p11) and Xp11.2 translocation lines. aCGH analyses identified all breakpoint regions, including an idic(X)(p11) line with two potential breakpoints, one breakpoint shared between two idic(X)(p11) lines and two Xp translocations that shared breakpoints with idic(X)(p11) lines. Four of the breakpoint regions included large inverted repeats composed of repetitive gene clusters and segmental duplications, which corresponded to regions of copy-number variation. These data indicate that the rearrangement sites on Xp11.2 that lead to isodicentric chromosome formation and translocations are probably not random and suggest that the complex repetitive architecture of this region predisposes it to rearrangements, some of which are recurrent.

De novo X/X translocation in a patient with secondary amenorrhea

A 46,X,t(X;X) (qter-->p22;;p22-->qter) karyotype was found in the chromosome analysis of a 22 years old female patient with secondary amenorrhea. Further analysis with fluorescence in situ hybridization indicated that the marker chromosome had one active and one inactive centromere originating from the X chromosome. RBG-banding showed that the derivative X chromosome was preferentially inactivated in cultured lymphocytes.