Molecular cytogenetic characterization of two Turner syndrome patients with mosaic ring X chromosome

Molecular and cytogenetic analysis of small supernumerary marker chromosomes in prenatal diagnosis

BACKGROUND

Small supernumerary marker chromosome (sSMC) is a structurally abnormal chromosome of unknown origin by conventional cytogenetics. The understanding of clinical significance of sSMC is still limited in prenatal diagnosis. The presence of sSMC poses a challenge for genetic counselling.

METHODS

We obtained the clinical information of 25 cases with sSMC. The fetal samples were subjected to multiple molecular and cytogenetic approaches including karyotype analysis, chromosomal microarray analysis, bacterial artificial chromosomes-on-beads assay, and fluorescence in situ hybridization.

RESULTS

Seven sSMCs were found to be r(X), and five of the cases terminated the pregnancy. Three markers were idic(15), and one of the cases was normal at birth. Two markers were i(12p), and both cases terminated the pregnancy. Other markers were r(Y) (outcome: normal at birth), i(18p) (outcome: stillbirth), der(15) (outcome: terminated), del(9) (outcome: terminated), dup(13) (outcome: follow-up loss), and derived from chromosome 21 (outcome: stillbirth). Seven markers were of unknown origin because not all methods were applied to them.

CONCLUSION

Applying multiple molecular and cytogenetic approaches could identify the origin and genetic content of sSMC to assist the genetic counselling in prenatal diagnosis.

Identification of a Small Supernumerary Marker Chromosome in a Turner Syndrome Patient with Karyotype mos 46,X,+mar/45,X

Turner Syndrome is characterized by a normal X chromosome and the partial or complete absence of a second sexual chromosome. Small supernumerary marker chromosomes are present in 6.6% of these patients. Because of the wide range of Turner syndrome karyotypes, it is difficult to establish a relationship with the phenotype of the patients. We present the case of a female patient with Turner syndrome, insulin resistance, type 2 diabetes, and intellectual disability. The karyotype revealed the presence of mosaicism with a monosomy X cell line and a second line with a small marker chromosome. FISH of two different tissues was used to identify the marker chromosome with probes for X and Y centromeres. Both tissues presented mosaicism for a two X chromosome signal, differing in the percentage of the monosomy X cell percentage. Comparative genomic hybridization with the CytoScan^TMHD assay was performed in genomic DNA from peripheral blood, allowing us to determine the size and breakage points of the small marker chromosome. The patient presents a phenotype that combines classic Turner syndrome features and unlikely ones as intellectual disability. The size, implicated genes, and degree of inactivation of the X chromosome influence the broad spectrum of phenotypes resulting from these chromosomes.

The past, present, and future for constitutional ring chromosomes: A report of the international consortium for human ring chromosomes

Human ring chromosomes (RCs) are rare diseases with an estimated newborn incidence of 1/50,000 and an annual occurrence of 2,800 patients globally. Over the past 60 years, banding cytogenetics, fluorescence in situ hybridization (FISH), chromosome microarray analysis (CMA), and whole-genome sequencing (WGS) has been used to detect an RC and further characterize its genomic alterations. Ring syndrome featuring sever growth retardation and variable intellectual disability has been considered as general clinical presentations for all RCs due to the cellular losses from the dynamic mosaicism of RC instability through mitosis. Cytogenomic heterogeneity ranging from simple complete RCs to complex rearranged RCs and variable RC intolerance with different relative frequencies have been observed. Clinical heterogeneity, including chromosome-specific deletion and duplication syndromes, gene-related organ and tissue defects, cancer predisposition to different types of tumors, and reproductive failure, has been reported in the literature. However, the patients with RCs reported in the literature accounted for less than 1% of its occurrence. Current diagnostic practice lacks laboratory standards for analyzing cellular behavior and genomic imbalances of RCs to evaluate the compound effects on patients. Under-representation of clinical cases and lack of comprehensive diagnostic analysis make it a challenge for evidence-based interpretation of clinico-cytogenomic correlations and recommendation of follow-up clinical management. Given recent advancements in genomic technologies and organized efforts by international collaborations and patient advocacy organizations, the prospective of standardized cytogenomic diagnosis and evidence-based clinical management for all patients with RCs could be achieved at an unprecedented global scale.

Characterization of a rare mosaic X-ring chromosome in a patient with Turner syndrome

BACKGROUND

Ring chromosomes can be formed by terminal breaks of two arms of a chromosome and their rejoining, leading to a loss of genetic material. They may also be formed by telomere-telomere fusions with no deletion, resulting in the formation of a complete ring. Mosaic X-ring chromosomes are extremely rare and have highly variable phenotypes. Here, we report a case with a mosaic X-ring chromosome in a patient with Turner syndrome, and we illustrate the unreported complicated mechanism using chromosome analysis and fluorescence in situ hybridization (FISH).

CASE PRESENTATION

A 10-year-old girl of short stature presenting Turner syndrome was admitted to our hospital. The patient's clinical characteristics were subsequently documented. Genetic analysis showed a karyotype of mostly 45,X[140]/46,X,r(X)[60]. The X ring chromosome was cytogenetically characterized as 45,X/46,X,r(X)(p22.32q21.1), with a length of approximately 74 Mb.

CONCLUSIONS

Taken together, we report a rare case with a mosaic X ring chromosome in Turner syndrome and we believe this case expands our collective knowledge of mosaic structural chromosomal disorders and provides new insight into clinical management and genetic counseling for Turner syndrome.

A rare case of mosaic ring turner syndrome with horseshoe kidney

Rearranged X chromosomes in Turner syndrome (TS) generally present with a mild phenotype, but in cases of ring X chromosomes, the incidence of intellectual disability and other congenital abnormalities can be significantly higher depending on the size of the ring and the involvement of X-inactive specific transcript (XIST) region. Here, we report a 17-year-old female who was referred for a cytogenetic analysis because of primary amenorrhoea. The patient, of normal intelligence, had been found to have traits of TS, especially short stature and some rare findings such as horseshoe kidney and short fourth toe. Cytogenetic analysis showed a mosaic 45, X/46, X and r(X) karyotype. Fluorescence in situ hybridisation analysis using sex chromosome probes permitted us to identify the marker as a ring X chromosome, detected in 30% of cells. The r(X) might include the XIST locus, which would have caused X-inactivation of this abnormal ring chromosome leading to mild phenotype in our patient but with atypical features present in the form of horseshoe kidney and short fourth toe.

Origin of the X-chromosome influences the development and treatment outcomes of Turner syndrome

Turner syndrome (TS) affects 1/2,500 live-born female infants. In the present study, we attempted to clarify the relationship between genetic factors (especially the X-chromosome origin), clinical features, body/sexual development, and treatment outcomes. We enrolled 39 female infants aged between 3 and 14 years. General demographic and clinical features were documented, and laboratory analysis of blood samples was performed. Subject karyotype was determined by G-banding of 50 peripheral white blood cells, and the parenteral origin of the retained X-chromosome was determined. Next, growth hormone (GH) treatment was prescribed for 12 months, with follow-ups performed as determined. For patient groups separated according to X-chromosome origin, the basal height, bone age, insulin-like growth factor (IGF)-1, and insulin-like growth factor binding protein-3 (IGFBP-3) levels were comparable; however, after the 12-month treatment, significant differences in the height increase and IGF-1 levels were observed. If the X-chromosome (or chromosomes) originated from both parents, the increase in height was less substantial, with lower serum IGF-1 levels. The uterine size, prolactin level, increased weight after treatment, and bone age difference after treatment negatively correlated with the mother’s age at the time of birth. The mother’s height at the time of birth demonstrated a negative correlation with the basal bone age difference and a positive correlation with the IGF-1 level. In summary, the retained X-chromosome derived from both parents is associated with poorer response to GH therapy. The mother’s age and height at the time of birth can strongly impact the patient’s body/sexual development and the response to GH treatment. Thus, the mother’s age and height at the time of birth and the parental origin of the X-chromosome should be carefully considered before developing a treatment plan for TS.

Coexistence of Growth Hormone Deficiency and Pituitary Microadenoma in a Child with Unique Mosaic Turner Syndrome: A Case Report and Literature Review

Turner syndrome (TS) is a genetic disorder with phenotypic heterogeneity caused by the monosomy or structural abnormalities of the X chromosome, and it has a prevalence of about 1/2500 females live birth. The variable clinical features of TS include short stature, gonadal failure, and skeletal dysplasia. The association with growth hormone (GH) deficiency or other hypopituitarism in TS is extremely rare, with only a few case reports published in the literature. Here, we report the first case of a patient with mosaic TS with complete GH deficiency and pituitary microadenoma, and we include the literature review. During the work-up of the patient for severe short stature, three GH provocation tests revealed peak GH levels of less than 5 ng/mL, which was compatible with complete GH deficiency. Sella magnetic resonance imaging showed an 8 mm non-enhancing pituitary adenoma with mild superior displacement of the optic chiasm. Karyotyping revealed the presence of ring chromosome X and monosomy X (46,X,r(X)/45,X/46,X,psu dic r(X;X)), which indicated a mosaic TS. It is important to consider not only chromosome analyses in females with short stature, but also the possibility of the coexistence of complete GH deficiency accompanying pituitary lesions in TS. In conclusion, the present study reports the first case of GH deficiency and pituitary adenoma in a patient with rare mosaic TS, which extends the genotype-phenotype spectrum for TS.

Genotype-phenotype correlation in 75 patients with small supernumerary marker chromosomes

Background

Small supernumerary marker chromosomes (sSMCs) are rare structural abnormalities in the population; however, they are frequently found in children or fetuses with hypoevolutism and infertile adults. sSMCs are usually observed first by karyotyping, and further analysis of their molecular origin is important in clinical practice. Next-generation sequencing (NGS) combined with Sanger sequencing helps to identify the chromosomal origins of sSMCs and correlate certain sSMCs with a specific clinical picture.

Results

Karyotyping identified 75 sSMCs in 74,266 samples (0.1% incidence). The chromosomal origins of 27 of these sSMCs were detected by sequencing-related techniques (NGS, MLPA and STR). Eight of these sSMCs are being reported for the first time. sSMCs mainly derived from chromosomal X, Y, 15, and 18, and some sSMC chromosomal origins could be correlated with clinical phenotypes. However, the chromosomal origins of the remaining 48 sSMC cases are unknown. Thus, we will develop a set of economical and efficient methods for clinical sSMC diagnosis.

Conclusions

This study details the comprehensive characterization of 27 sSMCs. Eight of these sSMCs are being reported here for the first time, providing additional information to sSMC research. Identifying sSMCs may reveal genotype-phenotype correlations and integrate genomic data into clinical care.

C-banding and AgNOR-staining were still effective complementary methods to indentify chromosomal heteromorphisms and some structural abnormalities in prenatal diagnosis

BACKGROUND

In prenatal diagnosis, CMA has begun to emerge as a favorable alternative to karyotype analysis, but it could not identify balanced translocations, triploidies, inversion and heteromorphisms. Therefore, conventional cytogenetic and specific staining methods still play an important role in the work-up of chromosome anomaly. This study investigated the application of C-banding and AgNOR-staining techniques in prenatal diagnosis of chromosomal heteromorphisms and some structure abnormalities.

RESULTS

Among the 2970 samples, the incidence of chromosomal heteromorphisms was 8.79% (261/2970). The most frequent was found to be chromosome Y (2.93%, 87/2970), followed by chromosome 1 (1.65 %, 49/2970), 9 (1.52 %, 45/2970), 22 (0.77 %, 23/2970) and 15 (0.64 %, 19/2970). We compared the incidence of chromosomal heteromorphisms between recurrent spontaneous abortion (RSA) group and control group. The frequency of autosomal hetermorphisms in RSA group was 7.63% higher than that in control group (5.78%), while the frequency of Y chromosomal heteromorphisms was 4.76% lower than that in control group (5.71%). Here we summarized 4 representative cases, inv (1) (p12q24), psu dic (4;17) (p16.3;p13.3), r(X)(p11; q21) and an isodicentric bisatellited chromosome to illustrate the application of C-banding or AgNOR-staining, CMA or NGS was performed to detect CNVs if necessary.

CONCLUSIONS

This study indicated that C-banding and AgNOR-staining were still effective complementary methods to identify chromosomal heteromorphisms and marker chromosomes or some structural rearrangements involving the centromere or acrocentric chromosomes. Our results suggested that there was no evidence for an association between chromosomal heteromorphisms and infertility or recurrent spontaneous abortions. Undoubtedly, sometimes we needed to combine the results of CMA or CNV-seq to comprehensively reflect the structure and aberration of chromosome segments. Thus, accurate karyotype reports and genetic counseling could be provided.