Multiple Small Supernumerary Marker Chromosomes Resulting from Maternal Meiosis I or II Errors

Supernumerary derivative 22 chromosome resulting from novel constitutional non-Robertsonian translocation: t(20;22)-Case Report

Background

Maternal non-Robertsonian translocation-t(20;22)(q13;q11.2) between chromosomes 20 and 22resulting in an additional complex small supernumerary marker chromosome as derivative (22)inherited to the proband is not been reported yet.

Case presentation

A 4 years old boy with a history of developmental delay, low set ears, and facial dysmorphism was presented to the genetic clinic. Periauricular pit, downward slanting eyes, medially flared eyebrows, downturned mouth corners, and micrognathia were observed. He had congenital heart defect with atrial septal defect (ASD), ventricular septal defect (VSD), and central nervous system (CNS) anomalies with the gross cranium. Karyotype analysis, Fluorescent in-situ hybridization analysis (FISH), and Chromosomal microarray analysis (CMA) were used to determine the chromosomal origin and segmental composition of the derivative 22 chromosome. Karyotype and FISH analyses were performed to confirm the presence of a supernumerary chromosome, and Microarray analysis was performed to rule out copy number variations in the proband's 22q11.2q12 band point. The probands' karyotype revealed the inherited der(22)t(20;22)(q13;q11.2)dmat. Parental karyotype confirmed the mother as the carrier, with balanced non-Robertsonian translocation-46,XX,t(20;22)(q13;q11.2).

Conclusion

The mother had a non-Robertsonian translocation t(20;22)(q13;q11.2) between chromosomes 20 and 22, which resulted in Emanuel syndrome in the proband. The most plausible explanation is 3:1 meiotic malsegregation, which results in the child inheriting derivative chromosome. The parental karyotype study aided in identifying the carrier of the supernumerary der(22), allowing future pregnancies with abnormal offspring to be avoided.

Genomic and Epigenetic Foundations of Neocentromere Formation

Centromeres are essential to genome inheritance, serving as the site of kinetochore assembly and coordinating chromosome segregation during cell division. Abnormal centromere function is associated with birth defects, infertility, and cancer. Normally, centromeres are assembled and maintained at the same chromosomal location. However, ectopic centromeres form spontaneously at new genomic locations and contribute to genome instability and developmental defects as well as to acquired and congenital human disease. Studies in model organisms have suggested that certain regions of the genome, including pericentromeres, heterochromatin, and regions of open chromatin or active transcription, support neocentromere activation. However, there is no universal mechanism that explains neocentromere formation. This review focuses on recent technological and intellectual advances in neocentromere research and proposes future areas of study. Understanding neocentromere biology will provide a better perspective on chromosome and genome organization and functional context for information generated from the Human Genome Project, ENCODE, and other large genomic consortia. Expected final online publication date for the Annual Review of Genetics, Volume 55 is November 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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.

Small supernumerary marker chromosomes (sSMC) and male infertility: characterization of five new cases, review of the literature, and perspectives

PURPOSE

To characterize small supernumerary marker chromosomes (sSMC) in infertile males RESEARCH QUESTION: Are molecular cytogenetic methods still relevant for the identification and characterization of sSMC in the era of next-generation sequencing?

METHODS

In this paper, we report five males with oligoasthenozoospermia or azoospermia with a history of recurrent pregnancy loss in partnership in four cases. R-banding karyotyping and fluorescence in situ hybridization (FISH) analysis were performed and showed sSMC in all five cases. Microdissection and reverse-FISH were performed in one case.

RESULTS

One sSMC, each, was derived from chromosome 15 and an X-chromosome; two sSMC were derivatives of chromosome 22. The fifth sSMC was a ring chromosome 4 complemented by a deletion of the same region 4p14 to 4p16.1 in one of the normal chromosomes 4. All markers were mosaics except one of sSMC(22).

CONCLUSION

Through this study, we emphasize the necessity of a proper combination of high-throughput techniques with conventional cytogenetic and FISH methods. This could provide a personalized diagnostic and accurate results for the patients suffering from infertility or RPL. We also highlight FISH analyses, which are essential tools for detecting sSMC in infertile patients. In fact, despite its entire composition of heterochromatin, sSMC can have effects on spermatogenesis by producing mechanical perturbations during meiosis and increasing meiotic nondisjunction rate. This would contribute to understand the exact chromosomal mechanism disrupting the natural and the assisted reproduction leading to offer a personalized support.

Molecular cytogenetic characterization of small supernumerary marker 15 in infertile male: A case report

Small supernumerary marker chromosomes (sSMCs) are defined as structurally abnormal chromosomes that may be detected pre- or postnataly in patients with developmental and/or mental retardation or infertility. sSMC on chromosome 15 accounts for the highest proportion of all sSMCs and may be detected in subfertile individuals. The present study reports the case of a male patient with oligoasthenoteratozoospermia and an sSMC. The sSMC was identified and characterized according to G-banding analysis, chromosomal microarray analysis (CMA) and fluorescence in situ hybridization (FISH) analysis. Chromosomal karyotype analysis suggested that the patient presented with 47,XY,+mar. CMA was used to characterize the sSMC, which revealed a 0.44-Mb microduplication in 6q25.3q26. Subsequently, FISH using centromere-specific probes for chromosomes 13/21, 14/22 and 15 was applied to identify the origin of the sSMC, which was finally determined to be inverted duplicated(15)(q11.2). It was hypothesized that heterochromatin in the sSMC is responsible for the patient's fertility problem. The presence of heterochromatin may disrupt regular meiosis, thereby affecting normal spermatogenesis. Impaired spermatogenesis in infertile males with an sSMC derived from chromosome 15 was also reviewed by searching published literature and the sSMC database (http://ssmc-tl.com/sSMC.html). For patients with low sperm parameters and complete absence of spermatozoa in the ejaculate, including infertile males with an sSMC with spermatozoa, intracytoplasmic sperm injection is considered as an effective assisted reproductive technique. It may be concluded that molecular cytogenetic techniques are critical tools for delineating sSMCs in infertile males and may be beneficial in identifying sSMC carriers to ensure they receive clinical genetic counseling.

A prenatal case with multiple supernumerary markers identified as derivatives of chromosomes 13, 15, and 20: molecular cytogenetic characterization and review of the literature

Multiple small supernumerary marker chromosomes (sSMCs) are among the rarest cytogenetic abnormalities as they represent roughly 1.4% of cases with sSMCs. We report on a prenatal case presenting de novo multiple sSMCs; these sSMCs were characterized by array CGH and FISH and resulted deriving from three different chromosomes: a der(13), a der(15) and a der(20). The co-presence of der(13), der(20), and der(15) have not been reported yet. The clinical consequences of this marker combination cannot be precisely predicted. However, according to the publicly available databases, the partial trisomies of chromosome 13 and 20 have probably a pathogenic effect. It is worth noting that a cooperative effect, due to interactions among genes harbored on the three derivatives, cannot be excluded, making the genetic counseling challenging.

Multiplex ligation dependent probe amplification - A useful, fast and cost-effective method for identification of small supernumerary marker chromosome in children with developmental delay and congenital heart defect

Small supernumerary marker chromosome (sSMC) is a rare chromosomal abnormality and is detected in about 0.3% in cases with multiple congenital anomalies (MCA) and/or developmental delay. Different techniques for investigation of cases with MCA and/or developmental delay are available ranging from karyotyping to molecular cytogenetic technique and ultimately multiplex ligation dependent probe amplification (MLPA). Here we present a patient with multiple congenital anomalies for which classical cytogenetic technique was used as a first step in diagnosis and the results being confirmed by MLPA. The karyotype disclosed a sSMC considered to be a fragment of chromosome 22. The MLPA analysis using SALSA MLPA probemix P064-C2 Microdeletion Syndromes-1B confirmed the karyotype results, and according to the manufacturer’s recommendation we performed another confirmation analysis with MLPA probemix P311-B1 Congenital Heart Disease and MLPA probemix P250-B2 DiGeorge. We also suspected an Emanuel syndrome and performed another MLPA analysis with SALSA MLPA probemix P036-E3 Subtelomeres Mix 1 and probemix P070-B3 Subtelomeres Mix 2B for investigation of subtelomeric region that revealed a duplication of 11q25 region and the confirmation was performed using SALSA MLPA probemix P286-B2 Human Telomere-11.

In conclusion, we consider that MLPA is a valuable method for identification of sSMC in children with developmental delay and congenital anomalies. Genetic diagnosis using different molecular techniques, such as MLPA, for increasing accuracy in identification of chromosomal structural aberrations has an important role in clinical diagnosis and in genetic counselling and our case explain the importance of using a specific laboratory technique for each stage of diagnosis.

Novel phenotype of 5p13.3-q11.2 duplication resulting from supernumerary marker chromosome 5: implications for management and genetic counseling

Background

Supernumerary marker chromosomes derived from chromosome 5 (SMC5) and 5p13 duplication syndrome are rare disorders, and phenotypic descriptions of patients are necessary to better define genotype-phenotype correlations for accurate, comprehensive genetic counseling. The purpose of this study is to highlight the unique findings of a patient with a 5p13.3-q11.2 duplication arising from a SMC5 and compare and contrast the phenotype with cases in the literature.

Case presentation

We report on an adult male with a 22 Mb duplication of chromosome 5p13.3-q11.2 resulting from a small SMC5. The patient has a history of prenatal polyhydramnios, dysmorphic features, respiratory issues, talipes equinovarus, hypotonia, developmental delay, and autistic features. The patient also has novel features of aortic dilation, pectus excavatum, kyphoscoliosis, and skin striae, suggestive of a connective tissue disorder. Despite these features he did not meet clinical diagnostic criteria for a well-characterized connective tissue disorder. Additional molecular genetic testing for syndromic and non-syndromic aortic aneurysms was negative.

Conclusions

Many of the patient’s features are consistent with individuals reported with 5p13 duplication syndrome and similar cases of SMC5, including polyhydramnios, macrocephaly, dolichocephaly, pre-auricular pits, arachnodactyly, respiratory problems, and developmental delays. It is unclear if the patient’s unique features of aortic dilation, pectus excavatum, kyphoscoliosis, and skin striae could be novel features of the SMC5 given its rarity and the few well-phenotyped adults in the literature. This report reviews the literature and provides additional phenotypic information to define the genotype-phenotype correlation of SMC5 and 5p13 duplication syndrome.