Tetrasomy 13q31.1qter due to an inverted duplicated neocentric marker chromosome in a fetus with multiple malformations

Prenatal identification of an inverted duplicated 13q marker chromosome with a neocentromere

In this case report, we describe a rare prenatal finding of a small marker chromosome. This marker chromosome corresponds to an inverted duplication of the 13q region 13q31.1q34 (or 13q31.1 → qter) with a neocentromere, detected during genetic analysis of a chorionic villus sample in a fetus with multiple congenital anomalies after a normal prenatal screening result by noninvasive prenatal testing.

Identification of partial trisomy 13q in two unrelated patients using single-nucleotide polymorphism array and literature overview

Background

Partial trisomy 13q is a less common chromosomal abnormality with a great clinical variability, among them, isolated partial trisomy 13q is extremely rare. Here, we report two new unrelated cases of partial trisomy 13q in Chinese families aiming to emphasize the genotype–phenotype correlation in partial trisomy 13q.

Methods

Enrolled in this study were two unrelated cases of partial 13q trisomy from two families in Quanzhou region South China. Karyotpe and single-nucleotide polymorphism (SNP) array analysis were employed to identify chromosome abnormalities and copy number variants in the families.

Results

A 72.9-Mb duplication in 13q14.11q34 region was identified using SNP array analysis in Patient 1 with an intellectual disability, developmental delay, seizures, gastric perforation, and other congenital malformations from a family with paternal inv(13)(p12q14.1). SNP array detection in Patient 2 revealed a 92.4-Mb duplication in 13q12.11q34 region combined with an 8.4-Mb deletion in Xq27.3q28 region with intellectual disability, developmental delay, cleft palate, and duplication of the cervix and the vagina. No chromosomal abnormality was elicited from the parents of Patient 2.

Conclusions

In this study, we presented two new unrelated cases of partial trisomy 13q with variable features in Chinese population, which may enrich the spectrum of the phenotypes partial trisomy 13q and further confirm the genotype–phenotype correlation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13039-022-00608-y.

Case Report: Prenatal Identification of a De Novo Mosaic Neocentric Marker Resulting in 13q31.1→qter Tetrasomy in a Mildly Affected Girl

Partial tetrasomy of distal 13q has a reported association with a variable phenotype including microphthalmia, ear abnormalities, hypotelorism, facial dysmorphisms, urogenital defects, pigmentation and skin defects, and severe learning difficulties. A wide range of mosaicism has been reported, which may, to some extent, account for the variable spectrum of observed phenotypes. We report here a pregnancy conceived using intrauterine insemination in a 32-year-old female with a history of infertility. Non-invasive prenatal screening (NIPS) was performed in the first trimester which reported an increased risk for trisomy 13. Follow-up cytogenetic workup using chorionic villus sampling (CVS) and amniotic fluid samples showed a mosaic karyotype with a small supernumerary marker chromosome (sSMC). Chromosomal microarray analysis (CMA) identified a mosaic 31.34 Mb terminal gain on chr13q31.1q34 showing the likely origin of the sSMC to distal chromosome 13q. Follow-up metaphase FISH testing suggested an inverted duplication rearrangement involving 13q31q34 in the marker chromosome and the presence of a neocentromere. At 21 months of age, the proband has a history of gross motor delay, hypotonia, left microphthalmia, strabismus, congenital anomaly of the right optic nerve, hemangiomas, and a tethered spinal cord. Postnatal chromosome analyses in buccal, peripheral blood, and spinal cord ligament tissues were consistent with the previous amniocentesis and CVS findings, and the degree of mosaicism varied from 25 to 80%. It is often challenging to pinpoint the chromosomal identity of sSMCs using banding cytogenetics. A combination of low-pass genome sequencing of cell-free DNA, chromosomal microarray, and FISH enabled the identification of the precise chromosomal rearrangement in this patient. This study adds to the growing list of clinically identified neocentric marker chromosomes and is the first described instance of partial tetrasomy 13q31q34 identified in a mosaic state prenatally. Since NIPS is now being routinely performed along with invasive testing for advanced maternal age, an increased prenatal detection rate for mosaic sSMCs in otherwise normal pregnancies is expected. Future studies investigating how neocentromeres mediate gene expression changes could help identify potential epigenetic targets as treatment options to rescue or reverse the phenotypes seen in patients with congenital neocentromeres.

Prenatal diagnosis and molecular cytogenetic characterization of a small supernumerary marker chromosome (sSMC) inherited from her mosaic sSMC(15) mother and a literature review

OBJECTIVE

We characterized a maternally inherited small supernumerary marker chromosome (sSMC) derived from chromosome 15 according to prenatal detection and made a review on the prenatal sSMC(15) cases with mosaic maternal inheritance.

CASE REPORT

A 29-year-old woman underwent amniocentesis at 19 weeks of gestation due to the high risk of Down syndrome in maternal serum screening. No abnormalities were observed in prenatal ultrasound findings. G-banding analysis revealed a karyotype of 47,XX,+mar. Subsequently, we recalled the couple back for chromosomal analysis. The father's karyotype was normal while the mother's karyotype was 47,XX,+mar[15]/46,XX[35]. Molecular genetic analysis was utilized to identify the marker chromosome. The chromosomal microarray analysis (CMA) results of the mother showed there existed microduplications in the locus of 14q32.33, 15q21.1, 19p12 and Xq26.2, respectively. Then Fluorescence in situ hybridization (FISH) using specific probes for chromosomes 13/21, 14/22, and 15 was applied on the mother and the fetus. And the marker chromosomes for the mother and the fetus were all finally identified as inv dup(15) (D15Z1++, SNRPN-, PML-), which illustrated that the fetus inherited the sSMC(15) from her mother. Finally, a healthy female infant was delivered with no phenotypic abnormalities at 39 weeks.

CONCLUSION

The combined utilization of the molecular genetic technologies, such as FISH and CMA, plays a critical role in the identification of the origins and genetic constitutions of sSMC, which would make a significant contribution to genetic counseling and prenatal diagnosis.

Small Supernumerary Ring Chromosome Derived from an Inverted Duplication of 13q11.2q14 in a Fetus with Coarctation of the Aorta

Here, we report a molecular characterization of a small supernumerary marker chromosome (sSMC) derived from the most proximal region of 13q present in a fetus with coarctation of the aorta at ultrasound examination during prenatal diagnosis. Cultured umbilical cord blood cells showed a de novo extra ring-shaped sSMC in 76% of the cells using a standard banding technique. SNP array revealed a tetrasomy of about 28.4 Mb in the long arm of chromosome 13 from band 13q11 to 13q14.11 in the fetus's cells. Metaphase/interphase FISH using specific probes located at 13q11, 13q12.11, and 13q14.11, respectively, demonstrated that the supernumerary ring chromosome was derived from an inverted duplication of the region 13q11q14.11 with a conventional centromere. To the best of our knowledge, this is the first time that an inverted duplication of the most proximal region 13q11q14.11 in a ring chromosome is characterized. The findings we presented here deepen our understanding of the clinical consequences of tetrasomy in this region and may be of help for further studies of critical regions in chromosome 13.

Hexasomy 13q31.3q34 due to two marker chromosomes with inverted duplication in a fetus with increased nuchal translucency

BACKGROUND

Small supernumerary marker chromosomes are structurally rearranged chromosomes that can be formed from different chromosomal fragments and cannot be identified using chromosomal banding analysis. Their examination has to be complemented by additional analyses like fluorescent in situ hybridization or array comparative genomic hybridization.

METHODS

We report on partial hexasomy of chromosome 13q in a fetus of a pregnant woman referred to genetic counseling because of increased fetal nuchal translucency and increased risk of trisomy 21 and trisomy 18 in first-trimester combined prenatal screening. Using chromosome banding analysis, in situ hybridization and array comparative hybridization we revealed the presence of two marker chromosomes with inverted duplication resulting in hexasomy of a 22.6 Mbp fragment in chromosomal region 13q31.3-13q34 with the lack of chromosome 13 centromere.

RESULTS

The fetus presented dysmorphic facial features, head and body disproportion, wide neck, ambiguous genitalia, incorrect position of the anus, and symmetrical shortening of the long bones were present in our described case. Some of these features were in accordance with other published cases. Other most often described features in tetrasomy were: microphtalmia or other major eye defects, ear abnormalities and deafness, hemangiomata, hypotelorism, severe learning disability and seizures. Despite a low risk of recurrence for small supernumerary marker chromosomes the possibility of germ line mosaicism exists, thus genetic counseling was offered to the examined family.

CONCLUSION

A full characterization of small supernumerary marker chromosomes in fetal karyotype is necessary for pregnancy prognosis and genetic counseling.

Review of literature: genes related to postaxial polydactyly

BACKGROUND

Postaxial polydactyly (PAP) is one of the commonest congenital malformations and usually is associated to several syndromes. There is no primary investigational strategy for PAP cases with single gene disorder in literature. PAP cases with single gene disorder can be classified according to common pathways and molecular basis. Molecular classification may help in diagnostic approach.

MATERIALS AND METHODS

All single gene disorders associated with PAP reported on PubMed and OMIM are analyzed and classified according to molecular basis.

RESULTS

Majority of genes related to cilia structure and functions are associated with PAP, so we classified them as ciliopathies and non-ciliopathies groups. Genes related to Shh-Gli3 pathway was the commonest group in non-ciliopathies.

CONCLUSION

Genes related to cilia are most commonly related to PAP due to their indirect relationship to Shh-Gli3 signaling pathway. Initially, PAP may be the only clinical finding with ciliopathies so those cases need follow up. Proper diagnosis is helpful for management and genetic counseling. Molecular approach may help to define pleiotropy.

Tetrasomy 13q32.2qter due to an apparent inverted duplicated neocentric marker chromosome in an infant with hemangiomas, failure to thrive, laryngomalacia, and tethered cord

BACKGROUND

Approximately 100 small supernumerary marker chromosomes (sSMCs) with a non-α-satellite neocentromere structure have been reported in the literature. Of the few derived from chromosome 13, five have consisted of inverted duplicated segment 13q32qter.

CASE REPORT

We herein describe the sixth case, characterized by genome wide SNP array, conventional cytogenetics and FISH studies. The de novo occurrence of the marker, the poor prognosis and the presence of hemangiomas are consistent with previous cases.

CONCLUSION

We hereby expand the clinical spectrum of this rare cytogenetic disorder and suggest a possible mechanism for the pathogenesis of associated congenital vascular malformations.

Neocentric X-chromosome in a girl with Turner-like syndrome

BACKGROUND

Neocentromeres are rare human chromosomal aberrations in which a new centromere has formed in a previously non-centromeric location. We report the finding of a structurally abnormal X chromosome with a neocentromere in a 15-year-old girl with clinical features suggestive of Turner syndrome, including short stature and primary amenorrhea.

RESULT

G-banded chromosome analysis revealed a mosaic female karyotype involving two abnormal cell lines. One cell line (84% of analyzed metaphases) had a structurally abnormal X chromosome (duplication of the long arm and deletion of the short arm) and a normal X chromosome. The other cell line (16% of cells) exhibited monosomy X. C-banding studies were negative for the abnormal X chromosome. FISH analysis revealed lack of hybridization of the abnormal X chromosome with both the X centromere-specific probe and the "all human centromeres" probe, a pattern consistent with lack of the X chromosome endogenous centromere. A FISH study using an XIST gene probe revealed the presence of two XIST genes, one on each long arm of the iso(Xq), required for inactivation of the abnormal X chromosome. R-banding also demonstrated inactivation of the abnormal X chromosome. An assay for centromeric protein C (CENP-C) was positive on both the normal and the abnormal X chromosomes. The position of CENP-C in the abnormal X chromosome defined a neocentromere, which explains its mitotic stability. The karyotype is thus designated as 46,X,neo(X)(qter- > q12::q12- > q21.2- > neo- > q21.2- > qter)[42]/45,X[8], which is consistent with stigmata of Turner syndrome. The mother of this patient has a normal karyotype; however, the father was not available for study.

CONCLUSION

To our knowledge, this is the first case of mosaic Turner syndrome involving an analphoid iso(Xq) chromosome with a proven neocentromere among 90 previously described cases with a proven neocentromere.