Usha R. Dutta

Cytogenetic abnormalities in 1162 couples with recurrent miscarriages in Southern region of India: report and review

PurposeThe purpose of the present study was to investigate the contribution of chromosomal anomalies and the frequency of a particular type of aberration in couples with recurrent miscarriages.MethodsA total of 1,162 couples with recurrent miscarriages were analyzed using G-banding and Fluorescence in situ hybridization where ever necessary.ResultsChromosomal anomalies were detected in 78 cases. This study describes majority of the cases with balanced reciprocal translocations. Among the abnormal karyotypes we also report for the first time three unique translocations involving (3;14), (18;22) and (X;22) chromosomes which were confirmed by molecular cytogenetic methods.ConclusionsThe review of literature and the overall incidence of the abnormalities suggest that chromosomal analysis in couples with recurrent miscarriages should be taken up by all the practioners at all levels. This not only helps to check the cytological abnormalities but also helps to correlate the recurrent abnormalities in a given population. Thus establishing and correlating the environmental and genetic condition of that particular phenotype and genotype.

Mosaic Down syndrome with a marker: Molecular cytogenetic characterization of the marker chromosome

Down syndrome is a complex disorder characterized by well defined and distinctive phenotypic features. Approximately 2-3% of all live-born Down individuals are mosaics. Here we report a boy with suspected Down syndrome showing mosaicism for two different cell lines where one cell line is unexpected. The cytogenetic analysis by G-banding revealed a karyotype of 47 XY+21 [20]/46,X+marker [30]. Further, molecular cytogenetic analysis with spectral karyotyping identified the marker as a derivative of Y chromosome. The delineation of Y chromosomal DNA was done by quantitative real-time PCR and aneuploidy detection by quantitative fluorescence PCR. The Y-short tandem repeats typing was performed to estimate the variation in quantity as well as to find out the extent of deletion on Y chromosome using STR markers. Fluorescence in situ hybridization using Y centromeric probe was also performed to confirm the origin of the Y marker. Further fine mapping of the marker was carried out with three bacterial artificial chromosome clones RP11-20H21, RP11-375P13, RP11-71M14, which defined the hypothetical position of the deletion. In our study we defined the extent of deletion of the marker chromosome and also discussed it in relation with mosaicism. This is the first report of mosaic Down syndrome combined with a second de novo mosaic marker derived from the Y chromosome.

ARHGEF9 disease: Phenotype clarification and genotype-phenotype correlation

Objective: We aimed to generate a review and description of the phenotypic and genotypic spectra of ARHGEF9 mutations. Methods: Patients with mutations or chromosomal disruptions affecting ARHGEF9 were identified through our clinics and review of the literature. Detailed medical history and examination findings were obtained via a standardized questionnaire, or if this was not possible by reviewing the published phenotypic features. Results: A total of 18 patients (including 5 females) were identified. Six had de novo, 5 had maternally inherited mutations, and 7 had chromosomal disruptions. All females had strongly skewed X-inactivation in favor of the abnormal X-chromosome. Symptoms presented in early childhood with delayed motor development alone or in combination with seizures. Intellectual disability was severe in most and moderate in patients with milder mutations. Males with severe intellectual disability had severe, often intractable, epilepsy and exhibited a particular facial dysmorphism. Patients with mutations in exon 9 affecting the proteins PH domain did not develop epilepsy. Conclusions: ARHGEF9 encodes a crucial neuronal synaptic protein; loss of function of which results in severe intellectual disability, epilepsy, and a particular facial dysmorphism. Loss of only the proteins PH domain function is associated with the absence of epilepsy.

A Balanced Reciprocal Translocation T (X;20) in A Girl with Seizures and Intellectual Disability Disrupting ARHGEF9

Results The chromosomal analyses revealed a translocation between the long arm of chromosome X and the short arm of chromosome 20 [46,X,t(X;20)(q12;p13)]. This result was confirmed by WCP FISH. Additionally, array CGH ruled out any gains or losses at the breakpoints or elsewhere in the genome. Also, X-inactivation studies by methylation specific PCR for HUMARA indicated skewed X-inactivation of the normal X chromosome. Breakpoint mapping of both derivative chromosomes was performed by serial FISH using BAC clones and RP11-943J20 from chromosome X showed split signals on patient derivative translocation chromosomes, indicating that this clone spanned the breakpoint. The breakpoint on 20p13 was mapped to a region of about 28 kb. Subsequent in silico analysis of the fine mapped breakpoint regions showed that on chromosome X, ARHGEF9 was likely disrupted by the chromosome rearrangement, whereas on chromosome 20 the breakpoint region does not seem to harbor a known gene. RT-PCR expression analysis of ARHGEF9 using RNA isolated from the patient’s lymphoblastoid cell line and a control suggested that in the patient the breakpoint maps between exons 1 and 2 of this gene. Further, the rearrangement has potentially resulted in fusion genes, suggested by the low expression of ARHGEF9 exons 2 to 10 in the patient.

A novel combined 15q11.2 duplication and a bisatellited supernumerary marker derived from chromosome 22: molecular characterization of the marker.

Supernumerary marker chromosomes (SMC) are heterogeneous group of chromosomes which are reported in variable phenotypes. Approximately 70% originate from acrocentric chromosomes. Here we report a couple with recurrent miscarriages and a SMC originating from an acrocentric chromosome. The cytogenetic analysis of the husband revealed a karyotype of 47,XY+marker whereas the wife had a normal karyotype. Analysis of SMC with C-banding showed the presence of a big centromere in the center and silver staining showed prominent satellites on both sides of the marker. Apparently, microarray analysis revealed a 2.1 Mb duplication of 15q11.2 region but molecular cytogenetic analysis by fluorescence in situ hybridization (FISH) with whole chromosome paint (WCP) 15 showed that the SMC is not of chromosome 15 origin. Subsequently, FISH with centromere 22 identified the SMC to originate from chromosome 22 which was also confirmed by WCP 22. Additional dual FISH with centromere 22 and Acro-p-arm probes confirmed the centromere 22 and satellites on the SMC. Further fine mapping of the marker with Bacterial Artificial Chromosome (BAC) clones; two on chromosome 22 and four on chromosome 15 determined the marker to possess only centromere 22 sequences and that the duplication 15 exists directly on chromosome 15. In our study, we had identified and characterized a SMC showing inversion duplication 22(p11.1) combined with a direct tandem duplication of 15q11.2. The possible genotype-phenotype in relation with the two rearrangements is discussed.

Identification and molecular cytogenetic characterization of a novel complex Y chromosome rearrangement in a boy with disorder of sexual development.

Ambiguous genitalia or disorder of the sexual development is a birth defect where the external genitals do not have the typical appearance of either a male or female. Here we report a boy with ambiguous genitalia and short stature. The cytogenetic analysis by G-banding revealed a small Y chromosome and an additional material on the 15p arm. Further, molecular cytogenetic analysis by Fluorescence in situ hybridization (FISH) using whole chromosome paint probes showed the presence of Y sequences on the 15p arm, confirming that it is a Y;15 translocation. Subsequent, FISH with centromere probe Y showed two signals depicting the presence of two centromeres and differing with a balanced translocation. The dicentric nature of the derivative 15 chromosome was confirmed by FISH with both 15 and Y centromeric probes. Further, the delineation of the Y chromosomal DNA was also done by quantitative real time PCR. Additional Y-short tandem repeat typing was performed to find out the extent of deletion on small Y chromosome. Fine mapping was carried out with 8 Y specific BAC clones which helped in defining the breakpoint regions. MLPA was performed to check the presence or absence of subtelomeric regions and SHOX regions on Y. Finally array CGH helped us in confirming the breakpoint regions. In our study we identified and characterized a novel complex Y chromosomal rearrangement with a complete deletion of the Yq region and duplication of the Yp region with one copy being translocated onto the15p arm. This is the first report of novel and unique Y complex rearrangement showing a deletion, duplication and a translocation in the same patient. The possible mechanism of the rearrangement and the phenotype-genotype correlation are discussed.

Precision in chromosome identification with leads in molecular cytogenetics: An illustrated review

Chromosomal aberrations are a major cause of human genetic diseases. Conventional cytogenetic banding techniques are the method of identification for both numerical and structural chromosomal abnormalities but with limited resolution. However, precise identification and characterization of the chromosomal abnormalities can only be achieved by advanced molecular cytogenetic techniques. These techniques are based mainly on fluorescence in situ hybridization, which have become an invaluable tool in the field of diagnostics. The advent of these molecular cytogenetic techniques has helped in the identification of chromosomal abnormalities to its minutest level. Apparently, the leads in molecular cytogenetic techniques have paved way for advanced molecular diagnosis, which now plays a significant role in both diagnostics and clinical research. These advances have led to the increased knowledge of the possible molecular mechanism involved in the chromosomal rearrangements and the genotype-phenotype correlation thus helping the patients towards better diagnosis and genetic counseling. This article highlights the advances in molecular cytogenetic techniques emphasizing the precision in identification of chromosomal rearrangements, and also illustrates few chromosomal abnormalities pediatric cases identified using these molecular cytogenetic techniques.

Breakpoint mapping of a novel de novo translocation t(X;20)(q11.1;p13) by positional cloning and long read sequencing

Disease associated chromosomal rearrangements often have break points located within disease causing genes or in their vicinity. The purpose of this study is to characterize a balanced reciprocal translocation in a girl with intellectual disability and seizures by positional cloning and whole genome sequencing. The translocation was identification by G- banding and confirmed by WCP FISH. Fine mapping using BAC clones and whole genome sequencing using Oxford nanopore long read sequencing technology for a 1.46 X coverage of the genome was done. The positional cloning showed split signals with BAC RP11-943 J20. Long read sequencing analysis of chimeric reads carrying parts of chromosomes X and 20 helped to identify the breakpoints to be in intron 2 of ARHGEF9 gene on Xp11.1 and on 20p13 between RASSF2 and SLC23A2 genes. This is the first report of translocation which successfully delineated to single base resolution using Nanopore sequencing. The genotype-phenotype correlation is discussed.

Whole exome sequencing identifies a novel 5 Mb deletion at 14q12 region in a patient with global developmental delay, microcephaly and seizures

Rett syndrome is a neurodevelopmental disorder affecting the nervous, musculoskeletal and gastroenteric systems. Affected individuals show normal neonatal development for 6-18 months followed by sudden growth arrest, psychomotor retardation and a broad spectrum of clinical features. Sequence variants in MECP2 gene have been identified as the major genetic etiology accounting for 90-95% of patients. Apart from MECP2, pathogenic sequence variants and copy number variants of FOXG1 gene lead to congenital type of Rett syndrome which is a more severe form and characterised by absence of early normal development as seen in classical Rett syndrome. In this report we describe a female child with global developmental delay, microcephaly and myoclonic seizures harbouring a 5 Mb deletion in 14q12 locus resulting in deletion of single copy of brain specific genes FOXG1, PRKD1 and NOVA1. Whole exome sequencing ruled out any possible role of other pathogenic single nucleotide variants and/or indels as the etiology for the observed phenotype. However, copy number variation analysis from the whole exome data detected a ~ 5 Mb microdeletion at the long arm of chromosome 14q12 region. The deletion was confirmed through array Comparative Genomic Hybridization and validated by quantitative PCR. Further, parents were analysed for mosaicism through metaphase Fluorescence in-situ Hybridisation. Our report broadens the phenotype of atypical Rett syndrome and reiterates the role of exome sequencing not only in detection of point mutation/small indels but also for detection of large deletions/duplication in coding regions.

The history of human cytogenetics in India—A review

It is 60years since the discovery of the correct number of chromosomes in 1956; the field of cytogenetics had evolved. The late evolution of this field with respect to other fields is primarily due to the underdevelopment of lenses and imaging techniques. With the advent of the new technologies, especially automation and evolution of advanced compound microscopes, cytogenetics drastically leaped further to greater heights. This review describes the historic events that had led to the development of human cytogenetics with a special attention about the history of cytogenetics in India, its present status, and future. Apparently, this review provides a brief account into the insights of the early laboratory establishments, funding, and the German collaborations. The details of the Indian cytogeneticists establishing their labs, promoting the field, and offering the chromosomal diagnostic services are described. The detailed study of chromosomes helps in increasing the knowledge of the chromosome structure and function. The delineation of the chromosomal rearrangements using cytogenetics and molecular cytogenetic techniques pays way in identifying the molecular mechanisms involved in the chromosomal rearrangement. Although molecular cytogenetics is greatly developing, the conventional cytogenetics still remains the gold standard in the diagnosis of various numerical chromosomal aberrations and a few structural aberrations. The history of cytogenetics and its importance even in the era of molecular cytogenetics are discussed.