Prenatal diagnosis of a trisomy 7 mosaic case: CMA, CNV-seq, karyotyping, interphase FISH, and MS-MLPA, which technique to choose?

OBJECTIVE: This study aims to perform a prenatal genetic diagnosis of a high-risk fetus with trisomy 7 identified by noninvasive prenatal testing (NIPT) and to evaluate the efficacy of different genetic testing techniques for prenatal diagnosis of trisomy mosaicism. METHODS: For prenatal diagnosis of a pregnant woman with a high risk of trisomy 7 suggested by NIPT, karyotyping and chromosomal microarray analysis (CMA) were performed on an amniotic fluid sample. Low-depth whole-genome copy number variation sequencing (CNV-seq) and fluorescence in situ hybridization (FISH) were used to clarify the results further. In addition, methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) was performed to analyze the possibility of uniparental disomy(UPD). RESULTS: Amniotic fluid karyotype analysis revealed a 46, XX result. Approximately 20% mosaic trisomy 7 was detected according to the CMA result. About 16% and 4% of mosaicism was detected by CNV-seq and FISH, respectively. MS-MLPA showed no methylation abnormalities. The fetal ultrasound did not show any detectable abnormalities except for mild intrauterine growth retardation seen at 39 weeks of gestation. After receiving genetic counseling, the expectant mother decided to continue the pregnancy, and follow-up within three months of delivery was normal. CONCLUSION: In high-risk NIPT diagnosis, a combination of cytogenetic and molecular genetic techniques proves fruitful in detecting low-level mosaicism. Furthermore, the exclusion of UPD on chromosome 7 remains crucial when NIPT indicates a positive prenatal diagnosis of trisomy 7.

Prenatal diagnosis of fetuses with absent/hypoplastic nasal bone in second-trimester using chromosomal microarray analysis.

BACKGROUND: Pathogenic copy number variants (pCNVs) are associated with fetal ultrasound anomalies, which can be efficiently identified through chromosomal microarray analysis (CMA). The primary objective of the present study was to enhance understanding of the genotype-phenotype correlation in fetuses exhibiting absent or hypoplastic nasal bones using CMA. METHODS: Enrolled in the present study were 94 cases of fetuses with absent/hypoplastic nasal bone, which were divided into an isolated absent/hypoplastic nasal bone group (n = 49) and a non-isolated group (n = 45). All pregnant women enrolled in the study underwent karyotype analysis and CMA to assess chromosomal abnormalities in the fetuses. RESULTS: Karyotype analysis and CMA detection were successfully performed in all cases. The results of karyotype and CMA indicate the presence of 11 cases of chromosome aneuploidy, with trisomy 21 being the most prevalent among them. A small supernumerary marker chromosome (sSMC) detected by karyotype analysis was further interpreted as a pCNV by CMA. Additionally, CMA detection elicited three cases of pCNVs, despite normal findings in their karyotype analysis results. Among them, one case of Roche translocation was identified to be a UPD in chromosome 15 with a low proportion of trisomy 15. Further, a significant difference in the detection rate of pCNVs was observed between non-isolated and isolated absent/hypoplastic nasal bone (24.44% vs. 8.16%, p < .05). CONCLUSION: The present study enhances the utility of CMA in diagnosing the etiology of absent or hypoplastic nasal bone in fetuses. Further, isolated cases of absent or hypoplastic nasal bone strongly suggest the presence of chromosomal abnormalities, necessitating genetic evaluation through CMA.

Chromosome analysis of 303 pregnancy losses in Mexico.

BACKGROUND: Chromosomal abnormalities are present in 50 to 60% of miscarriages and in 6 to 19% of stillbirths. Although microarrays are preferred for studying chromosomal abnormalities, many hospitals cannot offer this methodology. OBJECTIVE: To present the results of the cytogenetic analysis of 303 products of conception (POC), which included 184 miscarriages, 49 stillbirths and 17 cases of undefined age. MATERIAL AND METHODS: Karyotyping, fluorescence in situ hybridization, short tandem repeats and microarrays were used, depending on the type of loss and available sample. RESULTS: In 29 POCs we found maternal tissue and were eliminated from the analyses. Informative results were obtained in 250 (91.2 %)/274 cases; the karyotyping success rate was 80.7%; that of single nucleotide polymorphism microarrays, 94.5%; and that of fluorescence in situ hybridization and short tandem repeat, 100%. Cytogenetic abnormalities were observed in 57.6% of miscarriages and in 24.5% of stillbirths; 94% of total anomalies were numerical and 6% were submicroscopic. CONCLUSIONS: Karyotyping with simultaneous short tandem repeat study to rule out contamination of maternal cells is effective for studying miscarriages; in stillbirths, microarrays are recommended.

ANTECEDENTES: Las alteraciones cromosómicas están presentes en 50 a 60 % de los abortos espontáneos y en 6 a 19 % de los mortinatos. Aunque se prefieren los microarreglos para estudiarlos, numerosos hospitales no pueden ofrecerlos. OBJETIVO: Presentar los resultados del estudio citogenético de 303 productos de la concepción (POC), 184 se obtuvieron de abortos espontáneos, 49 fueron mortinatos y en 17 no se identificó la de edad gestacional. MATERIAL Y MÉTODOS: Se empleó cariotipo, hibridación in situ con fluorescencia, secuencias cortas repetidas en tándem y microarreglos, según el tipo de pérdida y la muestra disponible. RESULTADOS: En 29 POC se encontró tejido materno, por lo que fueron eliminados de los análisis. En 250 (91.2 %)/274 casos se obtuvieron resultados informativos; la tasa de éxito del cariotipo fue de 80.7 %; la de los microarreglos de SNP, de 94.5 %; y la de la hibridación fluorescente in situ y la repetición corta en tándem, de 100 %. Se observaron anomalías citogenéticas en 57.6 % de los abortos espontáneos y en 24.5 % de los mortinatos; 94 % de las anomalías fueron numéricas y 6 %, submicroscópicas. CONCLUSIONES: El cariotipo en conjunto con el estudio de secuencias cortas repetidas en tándem para descartar contaminación de células maternas es efectivo para estudiar abortos espontáneos; los microarreglos se recomiendan en los mortinatos.

Prenatal chromosomal microarray analysis and karyotyping in fetuses with isolated choroid plexus cyst: A retrospective case-control study.

OBJECTIVES: To evaluate the the diagnostic yield of chromosomal microarray analysis (CMA) in fetuses with isolated CPC (iCPC). METHODS: A total of 315 fetuses with iCPC (iCPC group) and 364 fetuses without abnormal ultrasound findings (control group) were recruited between July 2014 to March 2018. RESULTS: The overall diagnostic yield of chromosomal abnormalities by CMA and karyotyping in iCPC group was up to 4.1 %, higher than 1.4 % in the control group, p < 0.05. The detection rate of pathogenic or likely pathogenic copy number variants (CNVs) with clinical significance by CMA in iCPC group (1.3 %) was higher than in control group (0 %), p < 0.05. According to the type of chromosome abnormalities, the missed diagnosis rate of non-invasive prenatal testing (NIPT) was 1.6 % in our study. CONCLUSIONS: The presence of iCPC on ultrasound examination suggests a potential indication for genetic counseling. Karyotyping and chromosomal microarray analysis may be considered for fetuses with iCPC. It is important to be aware of the limitations of non-invasive prenatal testing, as there is a possibility of residual risk.

Performance of noninvasive prenatal screening for fetal sex chromosome aneuploidies in a cohort of 116,862 pregnancies.

BACKGROUND: Noninvasive prenatal screening (NIPS) has shown good performance in screening common aneuploidies. However, its performance in detecting fetal sex chromosome aneuploidies (SCAs) needs to be evaluated in a large cohort. RESEARCH DESIGN AND METHODS: In this retrospective observation, a total of 116,862 women underwent NIPS based on DNA nanoball sequencing from 2015 to 2022. SCAs were diagnosed based on karyotyping or chromosomal microarray analysis (CMA). Among them, 2,084 singleton pregnancies received karyotyping and/or CMA. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of NIPS for fetal SCAs were evaluated. RESULTS: The sensitivity was 97.7% (95%CI, 87.7-99.9), 87.3% (95% CI, 76.5-94.4), 96.1% (95%CI, 86.5-99.5), and 95.7% (95% CI, 78.1-99.9), the PPV was 25.8% (95%CI, 19.2-33.2), 80.9% (95%CI, 69.5-89.4), 79.0% (95%CI, 66.8-88.3), and 53.7% (95%CI, 37.4-69.3) for 45,X, 47,XXY, 47,XXX, and 47,XYY, respectively. The specificity was 94.1% (95%CI, 93.0-95.1) for 45,X, and more than 99.0% for sex chromosome trisomy (SCT). The NPV was over 99.0% for all. CONCLUSIONS: NIPS screening for fetal SCAs has high sensitivity, specificity and NPV. The PPV of SCAs was moderate, but that of 45,X was lower than that of SCTs. Invasive prenatal diagnosis should be recommended for high-risk patients.

Unbalanced X;Y translocations carrying SRY in prenatal settings: Clinical, molecular, and cytogenetic analysis of three cases.

BACKGROUND: Generally, the translocation of SRY onto one of the X chromosomes leads to 46, XX testicular disorders of sex development, a relatively rare condition characterized by the presence of testicular tissue with a 46, XX karyotype. Three prenatal cases of unbalanced X; Y translocation carrying SRY were identified in this study. METHODS: Structural variants were confirmed using single nucleotide polymorphism array and chromosomal karyotyping. X chromosome inactivation (XCI) was also analyzed. Detailed clinical features of the three cases were collected. RESULTS: We identified two fetuses with maternal inherited unbalanced X; Y translocations carrying SRY and skewed XCI presenting with normal female external genitalia, and one fetus with de novo 46, XX (SRY+) and random XCI manifested male phenotypic external genitalia. CONCLUSION: This study reports that cases with unbalanced X; Y translocations carrying SRY manifested a normal female external genitalia in a prenatal setting. We speculate that the skewed XCI mediates the silence of SRY. In addition, our study emphasizes that combining clinical findings with pedigree analysis is critical for estimating the prognosis of fetuses with sex chromosome abnormalities.

Cryptic MYC insertions in Burkitt lymphoma: New data and a review of the literature.

The occurrence of MYC-negative Burkitt lymphoma (BL) has been discussed for many years. The real frequency of the MYC insertion in MYC-negative BL is still unknown. Fine-needle aspiration biopsies of 108 consecutive patients with clinicopathologically suspected BL (suspBL) were evaluated by flow cytometry, classical cytogenetics, and fluorescence in situ hybridization (FISH). We found 12 cases (11%) without the MYC rearrangement by FISH with a MYC breakapart probe: two patients (1.9%) with cryptic MYC/IGH fusion (finally diagnosed as BL) and 10 patients (9.3%) with 11q gain/loss (finally diagnosed as Burkitt-like lymphoma with 11q aberration). The exact breakpoints of the cryptic MYC/IGH were investigated by next-generation sequencing. The MYC insertions' breakpoints were identified in PVT1 in the first case, and 42 kb upstream of 5'MYC in the second case. To date, a molecular characterization of the MYC insertion in BL has only been reported in one case. Detailed descriptions of our MYC insertions in a routinely and consecutively diagnosed suspBL cohort will contribute to resolving the issue of MYC negativity in BL. In our opinion, the presence of the MYC insertions in BL and other lymphomas might be underestimated, because routine genetic diagnostics are usually based on FISH only, without karyotyping.

Clinical utility of expanded NIPT for chromosomal abnormalities and etiology analysis of cytogenetic discrepancies cases.

PURPOSE: This study is to assess the performance of expanded noninvasive prenatal testing (NIPT) in detecting chromosome aneuploidies and chromosome copy number variants (CNVs), and elucidate the discordant cases between NIPT and fetal karyotype. METHODS: A total of 2139 single pregnancies have been recruited and sequenced with expanded NIPT. Karyotype analysis and CNV sequencing (CNV-seq) of amniotic fluid were performed in 22 of 23 high-risk, three low-risk NIPT pregnant women with abnormal ultrasound findings in the follow-up, and three non-reportable NIPT pregnant women. The genetic investigation of discordant results between NIPT and amniocytes in three cases was proceeded. Placental samples, fetal samples from the limb, hip, umbilical cord, and maternal peripheral blood leukocytes were collected for CNV-Seq. RESULTS: Expanded NIPT revealed a total of 23 positive pregnancies and yielded the overall positive predictive value (PPV) 65.2%. For T21, T18, and XXY, all the PPV was 100% respectively. For CNVs > 10 Mb and 5-10 Mb, the PPV was 42.8% and 16.7%, respectively. The genetic investigation of placental and fetal samples indicated different levels of placental and fetal mosaicism contributing to two of three verified discordant results. CONCLUSIONS: The results showed that screening for CNVs with expanded NIPT is promising although the accuracy rate remains insufficient. The different occurring time of mitotic non-disjunction of different chromosome in early development of embryo results in varying levels of chromosomal mosaicism in different placental and fetal tissues. The result highlights the significance of comprehensive cytogenetic validation of placental and fetal specimens with an inconsistent NIPT results.

Comprehensive copy number analysis of Y chromosome-linked loci for detection of structural variations and diagnosis of male infertility.

Infertility affects about 15% of heterosexual couples and male factors account for ~45-50% of clinical cases. Genetic factors play an important role in male infertility and thus we try to develop a cost-effective method for screening the genetic factors in male infertility. In our retrospective proof-of-concept study, we employed the high-throughput ligation-dependent probe amplification (HLPA) to examine the copy number by 115 genomic loci covering the Y chromosome, and 5 loci covering the X chromosome-specific region. We identified 8 sex chromosome aneuploid people from the low sperm concentration (LSC) group, and Y chromosome-specific microdeletion/duplications in 211 samples from the LSC group, and in 212 samples from the control group. 35 samples showed complete loss of AZFc (BPY2 to CDY1B deletion), which was not observed in controls. Nevertheless, a partial loss of AZFc (BPY2 to BPY2B deletion) was detected at comparable frequencies in both groups (68/211 vs. 108/212, respectively). And we further found structural variations in 28.6 and 26.9% samples from infertility and fertility groups. Moreover, we found that there were lower copy numbers for heterochromatic sequences in men with LSC. Especially, we reported that ultra-low relative copy number (RCN) (<0.5) type and low RCN (0.5 to <0.75) type in Yq12 were more often in the LSC group for the first time. Our results not only shed light on the potential role of low RCN in Yq12 in male infertility but also showed that HLPA can be a powerful and cost-effective tool for clinical screening in male infertility.

Optical Genome Mapping in Routine Human Genetic Diagnostics-Its Advantages and Limitations.

In recent years, optical genome mapping (OGM) has developed into a highly promising method of detecting large-scale structural variants in human genomes. It is capable of detecting structural variants considered difficult to detect by other current methods. Hence, it promises to be feasible as a first-line diagnostic tool, permitting insight into a new realm of previously unknown variants. However, due to its novelty, little experience with OGM is available to infer best practices for its application or to clarify which features cannot be detected. In this study, we used the Saphyr system (Bionano Genomics, San Diego, CA, USA), to explore its capabilities in human genetic diagnostics. To this end, we tested 14 DNA samples to confirm a total of 14 different structural or numerical chromosomal variants originally detected by other means, namely, deletions, duplications, inversions, trisomies, and a translocation. Overall, 12 variants could be confirmed; one deletion and one inversion could not. The prerequisites for detection of similar variants were explored by reviewing the OGM data of 54 samples analyzed in our laboratory. Limitations, some owing to the novelty of the method and some inherent to it, were described. Finally, we tested the successful application of OGM in routine diagnostics and described some of the challenges that merit consideration when utilizing OGM as a diagnostic tool.

The supernumerary B chromosome of maize: drive and genomic conflict.

The supernumerary B chromosome of maize is dispensable, containing no vital genes, and thus is variable in number and presence in lines of maize. In order to be maintained in populations, it has a drive mechanism consisting of nondisjunction at the pollen mitosis that produces the two sperm cells, and then the sperm with the two B chromosomes has a preference for fertilizing the egg as opposed to the central cell in the process of double fertilization. The sequence of the B chromosome coupled with B chromosomal aberrations has localized features involved with nondisjunction and preferential fertilization, which are present at the centromeric region. The predicted genes from the sequence have paralogues dispersed across all A chromosomes and have widely different divergence times suggesting that they have transposed to the B chromosome over evolutionary time followed by degradation or have been co-opted for the selfish functions of the supernumerary chromosome.

Highly divergent karyotypes and barcoding of the East African genus Gonatoxia Karsch (Orthoptera: Phaneropterinae).

East Africa is a hotspot of biodiversity of many orthopteran taxa, including bushcrickets. Gonatoxia Karsch, 1889 species are fully alate Phaneropterinae, which are perfectly adapted to the foliage of forests. We examined five species using combined cytogenetic and molecular data to determine the inter- and intraspecific genetic diversity. The variation in the diploid number of chromosomes in males ranged from 2n = 28 + X0 and 26 + X0 to 2n = 6 + X0. Fluorescence in situ hybridization showed from one to many 18S rDNA loci as well as interstitial sequences, especially in G. helleri. 18S rDNA loci coincided with active NOR and C-banding patterns. The isolation of populations of the species explains differences in the number of chromosomes (G. maculata), chromosomal polymorphism and chromosomal heterozygosity (G. helleri). Our molecular phylogeny based on the COI locus supported the monophyly of the genus Gonatoxia and separateness of the five examined species in accordance with their morphological features and chromosome numbers as well as the species' distribution.

Diagnostic Considerations in the Epilepsies-Testing Strategies, Test Type Advantages, and Limitations.

The role of genetics in epilepsy has been recognized for a long time. Over the past decade, genome-wide technologies have identified numerous genes and variants associated with epilepsy. In the clinical setting, a myriad of genetic testing options are available, and a subset of specific genetic diagnoses have management implications. Furthermore, genetic testing can be a dynamic process. As a result, fundamental knowledge about genetics and genomics has become essential for all specialists. Here, we review current knowledge of the genetic contribution to various types of epilepsy, provide an overview of types of genetic variants, and discuss genetic testing options and their diagnostic yield. We also consider advantages and limitations of testing approaches.

Measurement of Chromosomal Arms and FISH Reveal Complex Genome Architecture and Standardized Karyotype of Model Fish, Genus Carassius.

The widely distributed ray-finned fish genus Carassius is very well known due to its unique biological characteristics such as polyploidy, clonality, and/or interspecies hybridization. These biological characteristics have enabled Carassius species to be successfully widespread over relatively short period of evolutionary time. Therefore, this fish model deserves to be the center of attention in the research field. Some studies have already described the Carassius karyotype, but results are inconsistent in the number of morphological categories for individual chromosomes. We investigated three focal species: Carassius auratus, C. carassius and C. gibelio with the aim to describe their standardized diploid karyotypes, and to study their evolutionary relationships using cytogenetic tools. We measured length (q+plength) of each chromosome and calculated centromeric index (i value). We found: (i) The relationship between q+plength and i value showed higher similarity of C. auratus and C. carassius. (ii) The variability of i value within each chromosome expressed by means of the first quartile (Q1) up to the third quartile (Q3) showed higher similarity of C. carassius and C. gibelio. (iii) The fluorescent in situ hybridization (FISH) analysis revealed higher similarity of C. auratus and C. gibelio. (iv) Standardized karyotype formula described using median value (Q2) showed differentiation among all investigated species: C. auratus had 24 metacentric (m), 40 submetacentric (sm), 2 subtelocentric (st), 2 acrocentric (a) and 32 telocentric (T) chromosomes (24m+40sm+2st+2a+32T); C. carassius: 16m+34sm+8st+42T; and C. gibelio: 16m+22sm+10st+2a+50T. (v) We developed R scripts applicable for the description of standardized karyotype for any other species. The diverse results indicated unprecedented complex genomic and chromosomal architecture in the genus Carassius probably influenced by its unique biological characteristics which make the study of evolutionary relationships more difficult than it has been originally postulated.

Why Do Some Vertebrates Have Microchromosomes?

With more than 70,000 living species, vertebrates have a huge impact on the field of biology and research, including karyotype evolution. One prominent aspect of many vertebrate karyotypes is the enigmatic occurrence of tiny and often cytogenetically indistinguishable microchromosomes, which possess distinctive features compared to macrochromosomes. Why certain vertebrate species carry these microchromosomes in some lineages while others do not, and how they evolve remain open questions. New studies have shown that microchromosomes exhibit certain unique characteristics of genome structure and organization, such as high gene densities, low heterochromatin levels, and high rates of recombination. Our review focuses on recent concepts to expand current knowledge on the dynamic nature of karyotype evolution in vertebrates, raising important questions regarding the evolutionary origins and ramifications of microchromosomes. We introduce the basic karyotypic features to clarify the size, shape, and morphology of macro- and microchromosomes and report their distribution across different lineages. Finally, we characterize the mechanisms of different evolutionary forces underlying the origin and evolution of microchromosomes.

Practical Considerations for Using RNA Sequencing in Management of B-Lymphoblastic Leukemia: Malaysia-Singapore Acute Lymphoblastic Leukemia 2020 Implementation Strategy.

Despite the immense genetic heterogeneity of B-lymphoblastic leukemia [or precursor B-cell acute lymphoblastic leukemia (B-ALL)], RNA sequencing (RNA-Seq) could comprehensively interrogate its genetic drivers, assigning a specific molecular subtype in >90% of patients. However, study groups have only started to use RNA-Seq. For broader clinical use, technical, quality control, and appropriate performance validation are needed. We describe the development and validation of an RNA-Seq workflow for subtype classification, TPMT/NUDT15/TP53 variant discovery, and immunoglobulin heavy chain (IGH) disease clone identification for Malaysia-Singapore acute lymphoblastic leukemia (ALL) 2020. We validated this workflow in 377 patients in our preceding Malaysia-Singapore ALL 2003/Malaysia-Singapore ALL 2010 studies and proposed the quality control measures for RNA quality, library size, sequencing, and data analysis using the International Organization for Standardization 15189 quality and competence standard for medical laboratories. Compared with conventional methods, we achieved >95% accuracy in oncogene fusion identification, digital karyotyping, and TPMT and NUDT15 variant discovery. We found seven pathogenic TP53 mutations, confirmed with Sanger sequencing, which conferred a poorer outcome. Applying this workflow prospectively to the first 21 patients in Malaysia-Singapore ALL 2020, we identified the genetic drivers and IGH disease clones in >90% of patients with concordant TPMT, NUDT15, and TP53 variants using PCR-based methods. The median turnaround time was 12 days, which was clinically actionable. In conclusion, RNA-Seq workflow could be used clinically in management of B-cell ALL patients.

Diagnostic Utility of Gene Fusion Panel to Detect Gene Fusions in Fresh and Formalin-Fixed, Paraffin-Embedded Cancer Specimens.

Somatic gene fusions are common in leukemias/lymphomas and solid tumors. The detection of gene fusions is crucial for diagnosis. NanoString fusion technology is a multiplexed hybridization method that interrogates hundreds of gene fusions in a single reaction. This study's objective was to determine the performance characteristics and diagnostic utility of NanoString fusion assays in a clinical diagnostics laboratory. Validation using 100 positive specimens and 15 negative specimens by a combined reference standard of fluorescence in situ hybridization (FISH)/RT-PCR/next-generation sequencing (NGS) assays achieved 100% sensitivity in leukemias/lymphomas and 95.0% sensitivity and 100% specificity in solid tumors. Subsequently, 214 consecutive clinical cases, including 73 leukemia/lymphoma specimens and 141 formalin-fixed, paraffin-embedded solid tumor specimens, were analyzed by gene fusion panels across 638 unique gene fusion transcripts. A variety of comparator tests, including FISH panels, conventional karyotyping, a DNA-based targeted NGS assay, and custom RT-PCR testing, were performed in parallel. The gene fusion assay detected 31 gene fusions, including 16 in leukemia/lymphoma specimens and 15 in solid tumor specimens. The overall sensitivity, specificity, and accuracy of gene fusions detected by the gene fusion panel in all 329 specimens (validation and consecutive clinical specimens) tested in this study were 94.8%, 100%, and 97.9%, respectively, compared with FISH/RT-PCR/NGS assays. The gene fusion panel is a reliable approach that maximizes molecular detection of fusions among both fresh and formalin-fixed, paraffin-embedded cancer specimens.

Chromosomal Instability and Origin of B Chromosomes in the Amazonian Glass Tetra Moenkhausia oligolepis (Günther, 1864) (Characiformes, Characidae).

B chromosomes occur in different species of the small characid fishes of the genus Moenkhausia. These supernumerary elements, that do not recombine with chromosomes of the standard A complement and follow their own evolutionary mechanism vary in number, morphology, and distribution. Here, we show karyotypic data of individuals of 2 populations of Moenkhausia oligolepis of the Brazilian Amazon (Pedro Correia and Taboquinha streams, Tocantins river basin), both with a diploid number of 50 chromosomes and karyotypic formula of 10m + 32sm + 8a. In addition to the normal complement, we also observed the occurrence of B chromosomes in the 2 populations with intra- and interindividual variation ranging from 0 to 10 Bs, independent of sex. The C-banding pattern evidenced heterochromatic blocks located mainly in the pericentromeric region of the chromosomes, while the B chromosomes appeared euchromatic. Silver-stained nucleolus organizer regions were identified in multiples sites, and some of these blocks were positive when stained with chromomycin A3. The karyotype analysis and the application of whole-chromosome painting in populations of M. oligolepis reinforce the conservation of the basal diploid number for the genus, as well as the evolutionary tendency in these fishes to carry B chromosomes. Both populations turned out to be in different stages of stability and expansion of their B chromosomes. We further suggest that the origin of these chromosomes is due to the formation of isochromosomes. Here, we identified a pair of complement A chromosomes involved in this process.

Prenatal diagnosis of Pallister-Killian syndrome and literature review.

Pallister-Killian syndrome (PKS) is a rare sporadic genetic disorder usually caused by mosaicism of an extra isochromosome of 12p (i(12p)). This retrospective study analysed the prenatal ultrasound manifestations and molecular and cytogenetic results of five PKS foetuses. Samples of amniotic fluid and/or cord blood, skin biopsy and placenta were collected. Conventional karyotyping and single nucleotide polymorphism array (SNP array) were performed on all the amniotic fluid or cord blood samples. Copy number variants sequencing (CNV-seq) and fluorescence in situ hybridization (FISH) were also used for the validation for one foetus. All the five foetuses were from pregnancies with advanced parental age. Two foetuses involved structural abnormalities and one foetus had only soft markers, all of which included increased nuchal translucency. The rest two foetuses had normal ultrasounds in the second trimester, which has rarely been reported before. The karyotype revealed typical i(12p) in four cases and a small supernumerary marker chromosome consisting of 12p and 20p in the remaining one case. The proportion of cells with i(12p) ranged from 0 to 100% in cultural cells, while SNP array results suggested 2-4 copies of 12p. For one foetus, metaphase FISH showed normal results, but the interphase FISH suggested cell lines with two, three and four copies of 12p in the amniotic fluid. Advanced parental age may be an important risk factor for PKS, and there were no typical ultrasound manifestations related to PKS. A combination of karyotype analysis and molecular diagnosis is an effective method for the diagnosis of PKS.