[Application of optical genome mapping technology for the detection of chromosomal structural variations].

OBJECTIVE: To assess the value of optical genome mapping (OGM) for the detection of chromosomal structural abnormalities including ring chromosomes, balanced translocations, and insertional translocations. METHODS: Clinical data of four patients who underwent pre-implantation genetic testing concurrently with OGM and chromosomal microarray analysis at the Center of Reproductive Medicine of the Sixth Affiliated Hospital of Sun Yat-sen University from January to October 2022 due to chromosomal structural abnormalities were selected as the study subjects. Some of the results were verified by multi-color fluorescence in situ hybridization. RESULTS: The OGM has successfully detected a balanced translocation and fine mapped the breakpoints in a patient. Among two patients with insertional translocations, OGM has provided more refined breakpoint locations than karyotyping analysis in a patient who had chromosome 3 inserted into chromosome 6 and determined the direction of the inserted fragment. However, OGM has failed to detect the chromosomal abnormality in a patient with chromosome 8 inserted into the Y chromosome. It has also failed to detect circular signals in a patient with ring chromosome mosaicism. CONCLUSION: OGM has successfully detected chromosomal structural variations in the four patients and provided assistance for their diagnosis.

Bilateral Cleft Lip and Palate in Ring Chromosome 7 Syndrome: A Case Report and Review of Clinical Characteristics.

This report presents a case of ring chromosome 7 syndrome with bilateral cleft lip and palate. A four-year-old boy presented with bilateral cleft lip and palate, microcephaly, clenched toes, cafe-au-lait spots, a history of epilepsy, and severe intellectual disability. Genetic karyotyping revealed 46 XY r(7) (p22q36). His cheiloplasty and delayed palatoplasty were successful. A review of 22 previous r(7) patients revealed that 22.7% had cleft lip and/or palate. This case demonstrates the importance of a multidisciplinary evaluation for cleft patients, particularly those with syndromic features and global developmental delay.

Live-born autosomal ring chromosomes at the Johns Hopkins Hospital Cytogenomics Laboratory: Case series-Spanning 52 years of experience in a single center.

Ring chromosomes (RCs) are a structural aberration that can be tolerated better in acrocentric or gonosomal chromosomes. Complete RCs arise from telomere-telomere fusions. Alternatively, genomic imbalances corresponding to the ends of the chromosomal arms can be seen with RC formation. RCs are unstable in mitosis, result in mosaicism, and are associated with a "ring syndrome," which presents with growth and development phenotypes and differs from those features more frequently observed with pure terminal copy number changes. Due to variability in mosaicism, size, and genomic content, clear genotype-phenotype correlations may not always be possible. Given the rarity of RCs, this historical data is invaluable. We performed a retrospective review of individuals bearing RCs to investigate the incidence in our laboratory. This work details the methods and features seen in association with twenty-three autosomal RCs. In decreasing order, the most frequently seen autosomal RCs were 18, 22, 4, 13, 17, and 9. The additional cases detail clinical and cytogenomic events similar to those reported in RCs. As methodologies advance, insights may be gleaned from following up on these cases to improve genotype-phenotype correlations and understand the cryptic differences or other predisposing factors that lead to ring formation and development.

[Prenatal genetic diagnosis of a case with ring chromosome 13].

OBJECTIVE: To carry out cyto- and molecular genetic analysis for a fetus with a ring chromosome identified through non-invasive prenatal testing (NIPT). METHODS: A pregnant woman presented at the Shengjing Hospital Affiliated to China Medical University on May 11, 2021 was selected as the study subject. Maternal peripheral blood sample was screened by NIPT, and G-banded chromosomal karyotyping was carried out on amniotic fluid and peripheral blood samples from the couple. The fetus and the pregnant woman were also subjected to genomic copy number variation sequencing (CNV-seq), chromosomal microarray analysis (CMA), and fluorescence in situ hybridization (FISH) assay. RESULTS: NIPT result suggested that the fetus had monomeric mosaicism or fragment deletion on chromosome 13. G banded chromosomal analysis showed that both the fetus and its mother had a karyotype of 47,XX,der(13)(pter→p11::q22→q10),+r(13)(::p10::q22→qter::), whilst her husband had a normal karyotype. FISH has verified the above results. No abnormality was detected with CNV-seq and CMA in both the fetus and the pregnant woman. CONCLUSION: The ring chromosome 13 in the fetus has derived from its mother without any deletion, duplication and mosaicism. Both the fetus and the pregnant woman were phenotypically normal.

Molecular characterization of de novo ring chromosome 21 in a child with seizures, growth retardation, and multiple congenital anomalies.

The ring chromosome 21[r(21)] syndrome is a rare disorder, and mainly occurs as a de novo event. However, a wide variation of the phenotype has been reported in r(21) cases depending on breakpoints, loss of genetic material, and mosaicism of cells with r(21) and monosomy 21, causing copy number alterations. A 29-month-old female was referred to the centre for seizures, developmental delay, microcephaly, hypotonia, deafness, and other congenital abnormalities. Physical examination revealed short stature and multiple facial dysmorphism. She was unable to sit, walk or stand by herself. Cytogenetic study with GTG banding revealed a karyotype of mos 46,XX,r(21)(p11.1q22.12)[70]/45,XX,-21[10]/47,XX,r(21),+r(21)[1]/46,XX[10]. Additionally, molecular cytogenetics refined the breakpoints and characterized the deleted region (RP11-410P24/CHR21: 32849565-33019511) in the clone with the r(21) as ~12-14 Mb contiguous region at 21q22.12 to 21qter. The present study has accurately detected copy number alterations caused by ring chromosome formation. The basis of the UCSC Genome Browser on Human (GRCh38/hg38) analysis suggests hemizygous expression of a deleted critical region of chromosome 21 in ring chromosome cell lines. This is likely to be the underlying cause of the present phenotypes in the patient. Overall, the genotype-phenotypic correlation in r(21) cases remains widely diverse, most likely due to tissue-specific mosaicism of the 45, XX,-21 cell line.

Response to growth hormone therapy in ring chromosome 15: Review and evidence from a new case on possible beneficial effect in neurodevelopment.

Type 1 Insulin-like Growth Factor Receptor(IGF1R) plays a fundamental role in normal growth and development. Its disruption is usually characterized by severe intrauterine and postnatal growth retardation, microcephaly and neurodevelopmental delay.The efficacy of recombinant human growth hormone treatment remains a challenge for children with IGF1 resistance and pathogenic mutations of IGF1R, with limited data in patients carrying the most severe form of IGF1R defect, the ring chromosome 15. SUBJECT AND METHOD: We tested a high dose of rhGH in a new patient with ring chromosome 15, as confirmed by karyotype and CGH array. We performed a systematic review, and all published r(15) syndrome cases treated by growth hormone(GH) up to April 2023 were searched, and their response to GH therapy was recorded and summarized. RESULTS: Twelve patients with ring chromosome 15 received GH therapy according to a literature review. We expand the spectrum by the 13th case treated by GH, and we report an impressive improvement in intellectual performance and progressive catch-up growth after 5 and 20 months of follow-up. By introducing our new case in the analysis, the sex ratio was 3:10, and GH therapy was started at the age of 5.5 (3/9.4) (years) for an age of diagnosis of 4.75 (1.3/9.5) (years). The height before GH therapy was -5.1(-5.9/-4.1) SDS. The median duration of treatment was 1.7(0.9/2) (years), with a median height gain of 1(0.3/1.8) SDS and an improvement in growth velocity of 4.1(2.8/5.3) (cm/year). CONCLUSION: GH seems to be effective for r(15) syndrome patients with short stature.

[Clinical features and genetic analysis of two fetuses with ring chromosome 21 mosaicism].

OBJECTIVE: To investigate the perinatal clinical phenotype and genetic characteristics of two fetuses with ring chromosome 21 mosaicisms. METHODS: Two fetuses who were diagnosed at the Xiamen Maternal and Child Health Care Hospital in November 2021 were selected as the study subjects. Clinical data of the two fetuses were collected. Conventional G-banded karyotyping and chromosomal microarray analysis (CMA) were carried out for the fetuses and their parents. RESULTS: Prenatal ultrasonography of fetus 1 has revealed absence of nasal bone, ventricular septal defect, persistent left superior vena cava, and mild tricuspid regurgitation. Chromosomal karyotyping was 46,X?,dic r(21;21)(p12q22;q22p12)[41]/45,X?,-21[9]. CMA has revealed a 30.00 Mb quadruplication at 21q11.2q22.3 and a 3.00 Mb deletion at 21q22.3. For fetus 2, ultrasonography has revealed pointed echo of the nasal bone. The fetus was found to have a karyotype of 46,X?,r(21)(p12q22)[83]/45,X?,-21[14]/46,X?,dic r(21;21)(p12q22;q22p12)[3]. CMA has revealed a 5.10 Mb quadruplication at 21q22.12q22.3 and a 2.30 Mb deletion at 21q22.3. CONCLUSION: The perinatal phenotype of the two fetuses with ring chromosome 21 mosaicisms is related to the duplication of chromosomal segments near the breakpoints of the chromosomal deletions. The combined chromosomal karyotyping and CMA has enabled prenatal diagnosis and genetic counseling for these families.

A rare ring chromosome 21 abnormality is associated with azoospermia in two different phenotypically normal cases.

Azoospermia can be diagnosed with spermiogram analysis, and karyotyping is the golden standard to explain the etiology. In this study, we investigated two male cases with azoospermia and male infertility for chromosomal abnormalities. Their phenotypes and physical and hormonal examinations were both normal. In karyotyping G-banding and NOR staining, a rare ring chromosome 21 abnormality was detected in the cases and no microdeletion in chromosome Y. Ring abnormality, deletion size, and deleted regions were shown with subtelomeric FISH (.ish r(21)(p13q22.3?)(D21S1446-)) and array CGH analyses. Due to the findings, bioinformatics, protein, and pathway analyses were done to detect a candidate gene through common genes in two cases' deleted regions or ring chromosome 21.

Consensus recommendations on counselling in Phelan-McDermid syndrome, with special attention to recurrence risk and to ring chromosome 22.

This paper focuses on genetic counselling in Phelan-McDermid syndrome (PMS), a rare neurodevelopmental disorder caused by a deletion 22q13.3 or a pathogenic variant in SHANK3. It is one of a series of papers written by the European PMS consortium as a consensus guideline. We reviewed the available literature based on pre-set questions to formulate recommendations on counselling, diagnostic work-up and surveillance for tumours related to ring chromosome 22. All recommendations were approved by the consortium, which consists of professionals and patient representatives, using a voting procedure. PMS can only rarely be diagnosed based solely on clinical features and requires confirmation via genetic testing. In most cases, the family will be referred to a clinical geneticist for counselling after the genetic diagnosis has been made. Family members will be investigated and, if indicated, the chance of recurrence discussed with them. Most individuals with PMS have a de novo deletion or a pathogenic variant of SHANK3. The 22q13.3 deletion can be a simple deletion, a ring chromosome 22, or the result of a parental balanced chromosomal anomaly, influencing the risk of recurrence. Individuals with a ring chromosome 22 have an increased risk of NF2-related schwannomatosis (formerly neurofibromatosis type 2) and atypical teratoid rhabdoid tumours, which are associated with the tumour-suppressor genes NF2 and SMARCB1, respectively, and both genes are located on chromosome 22. The prevalence of PMS due to a ring chromosome 22 is estimated to be 10-20%. The risk of developing a tumour in an individual with a ring chromosome 22 can be calculated as 2-4%. However, those individuals who do develop tumours often have multiple. We recommend referring all individuals with PMS and their parents to a clinical geneticist or a comparably experienced medical specialist for genetic counselling, further genetic testing, follow-up and discussion of prenatal diagnostic testing in subsequent pregnancies. We also recommend karyotyping to diagnose or exclude a ring chromosome 22 in individuals with a deletion 22q13.3 detected by molecular tests. If a ring chromosome 22 is found, we recommend discussing personalised follow-up for NF2-related tumours and specifically cerebral imaging between the age of 14 and 16 years.

The relationship of the efficiency of energy conversion into growth as an indicator for the determination of the optimal dose for mutation breeding with the appearance of chromosomal abnormalities and incomplete mitosis after gamma irradiation of kernels of Triticum turgidum ssp. durum L.

The study aim was to determine the optimal gamma irradiation dose for mutation breeding in Triticum turgidum ssp. durum L. Root, shoot and seedling growth, as well as the efficiency of energy conversion into growth were determined to examine the growth retardation effects of gamma irradiation that are the result of DNA damage (bridges, ring chromosomes, micronuclei, incomplete mitosis) in Triticum turgidum ssp. durum L. The kernels were irradiated with doses of 50, 150, 250 and 350 Gy using a 60Cobalt gamma-ray source. The kernels were placed in germination paper at 25 °C to grow for a 132 h period for the determination of shoot and root growth and the efficiency of energy conversion into growth. Root tips were collected and fixated over a 47.5 h growth period for the determination of the chromosomal abnormalities and incomplete mitosis. The control differed highly significantly (p < 0.01) from irradiated samples at all doses in root growth and from 250 to 350 Gy samples in shoot growth and the efficiency of energy conversion into growth. There was a highly significant (p < 0.01) increase in the number of bridges and micronuclei between 50 Gy samples and samples irradiated with the higher irradiation doses while 50 Gy samples differed only from 250 and 350 Gy samples regarding ring chromosomes and interphase cells with incomplete mitosis. Root and seedling growth on the one hand and the efficiency of energy conversion into growth on the other were found to be measuring different effects of gamma irradiation on plant growth. The latter was used for the determination of the optimal dose for mutation breeding as 155.52 Gy.

Optical Genome Mapping Reveals and Characterizes Recurrent Aberrations and New Fusion Genes in Adult ALL.

(1) Background: In acute lymphoblastic leukemia (ALL) the genetic characterization remains challenging. Due to the genetic heterogeneity of mutations in adult patients, only a small proportion of aberrations can be analyzed with standard routine diagnostics. Optical genome mapping (OGM) has recently opened up new possibilities for the characterization of structural variants on a genome-wide level, thus enabling simultaneous analysis for a broad spectrum of genetic aberrations. (2) Methods: 11 adult ALL patients were examined using OGM. (3) Results: Genetic results obtained by karyotyping and FISH were confirmed by OGM for all patients. Karyotype was redefined, and additional genetic information was obtained in 82% (9/11) of samples by OGM, previously not diagnosed by standard of care. Besides gross-structural chromosome rearrangements, e.g., ring chromosome 9 and putative isodicentric chromosome 8q, deletions in CDKN2A/2B were detected in 7/11 patients, defining an approx. 20 kb minimum region of overlap, including an alternative exon 1 of the CDKN2A gene. The results further confirm recurrent ALL aberrations (e.g., PAX5, ETV6, VPREB1, IKZF1). (4) Conclusions: Genome-wide OGM analysis enables a broad genetic characterization in adult ALL patients in one single workup compared to standard clinical testing, facilitating a detailed genetic diagnosis, risk-stratification, and target-directed treatment strategies.

Status Epilepticus in Chromosomal Disorders Associated with Epilepsy: A Systematic Review.

Status Epilepticus (SE) is a neurological emergency resulting from the failure of mechanisms of seizure termination or from the initiation of mechanisms that lead to prolonged seizures. The International League Against Epilepsy (ILAE) identified 13 chromosomal disorders associated with epilepsy (CDAE); data regarding SE occurrence in these patients is lacking. A systematic scoping review was conducted to outline current literature evidence about clinical features, treatments, and outcomes of SE in pediatric and adult patients with CDAE. A total of 373 studies were identified with the initial search; 65 of these were selected and regarded as SE in Angelman Syndrome (AS, n = 20), Ring 20 Syndrome (R20, n = 24), and other syndromes (n = 21). Non-convulsive status epilepticus (NCSE) is frequently observed in AS and R20. No specific, targeted therapies for SE in CDAE are available to date; anecdotal reports about SE treatment are described in the text, as well as various brief- and long-term outcomes. Further evidence is needed to precisely portray the clinical features, treatment options, and outcomes of SE in these patients.

[Clinical phenotype and genetic analysis of twelve children with ring chromosomes].

OBJECTIVE: To explore the prevalence and clinical manifestations of ring chromosomes among children featuring abnormal development. METHODS: From January 2015 to August 2021, 7574 children referred for abnormal development were selected, and their peripheral blood samples were subjected to G-banded chromosomal karyotyping analysis. RESULTS: Twelve cases of ring chromosomes were detected, which have yielded a prevalence of 0.16% and included 1 r(6), 2 r(9), 1 r(13), 1 r(14), 2 r(15), 1 r(21) and 3 r(X). The children had various clinical manifestations including growth and mental retardation, limb malformation, and congenital heart disease. For two children with r(9) and two with r(15) with similar breakpoints, one child with r(9) and one with r(15) only had growth retardation, whilst another with r(9) and another with r(15) also had peculiar facies and complex congenital heart disease. The r(X) has featured some manifestations of Turner syndrome. CONCLUSION: Ring chromosomes are among the common causes for severe growth and mental retardation in children with diverse clinical phenotypes. Clinicians should pay attention to those with developmental anomalies and use chromosomal analysis to elucidate their genetic etiology.

[Genetic features of a case with mosaic ring chromosome 4 and a review of the literature].

OBJECTIVE: To explore the genetic basis, clinical phenotype and pathogenesis for a child with mosaicism ring chromosome 4. METHODS: Clinical data of the child was collected. Peripheral blood chromosomal karyotype G banding analysis, chromosomal microarray analysis (CMA), fluorescence in situ hybridization (FISH) were carried out for the child, in addition with a review of the literature. RESULTS: The child was born full-term with low birth weight, facial dysmorphism, patent ductus arteriosus and ventricular septal defect. His karyotype was determined as mos46,XY,r(4)(p16.3q35.2)[259]/45,XY,-4[25]/47,XY,r(4)(p16.3q35.2), +r(4)(p16.3q35.2)[8]/46,XY,der(4)del(4)(p16.3)inv(4)(p16.3q31.1)[6]/46,XY,dic?r(4;4)(p16.3q35.2;p16.3q35.2)[4]/48,XY,r(4)(p16.3q35.2),+r(4)(p16.3q35.2)×2[3]/46,XY,r(4)(p1?q2?)[2]; CMA result was arr[GRCH37]4p16.3(68 345-2 981 614)×1; FISH result was 45,XY,-4[12]/45,XY,-4×2,+mar1.ish r1(4)(WHS-,D4Z1+)[1]/ 46,XY,-4,+mar1.ishr1(4)(WHS-,D4Z1+)[73]/46,XY,-4,+mar2.ishr2(4)(WHS-,D4Z1++)[1]/47,XY,-4,+mar1×2.ishr1(4) (WHS-, D4Z1+)×2[4]/46,XY,del(4)(p16.3).ish del(4)(p16.3)(WHS-,D4Z1+)[9]. CONCLUSION: In this case, the ring chromosome 4 as a de novo variant has produced a number of cell lines during embryonic development and given rise to mosaicism. The clinical phenotype of ring chromosome 4 is variable. The instability of the ring chromosome itself, presence of mosaicism, chromosome breakpoint and range of deletion and/or duplication may all affect the ultimate phenotype.

Recurring germline mosaicism in a family due to reversion of an inherited derivative chromosome 8 from an 8;21 translocation with interstitial telomeric sequences.

BACKGROUND: Mosaicism for chromosomal structural abnormalities, other than marker or ring chromosomes, is rarely inherited. METHODS: We performed cytogenetics studies and breakpoint analyses on a family with transmission of mosaicism for a derivative chromosome 8 (der(8)), resulting from an unbalanced translocation between the long arms of chromosomes 8 and 21 over three generations. RESULTS: The proband and his maternal half-sister had mosaicism for a der(8) cell line leading to trisomy of the distal 21q, and both had Down syndrome phenotypic features. Mosaicism for a cell line with the der(8) and a normal cell line was also detected in a maternal half-cousin. The der(8) was inherited from the maternal grandmother who had four abnormal cell lines containing the der(8), in addition to a normal cell line. One maternal half-aunt had the der(8) and an isodicentric chromosome 21 (idic(21)). Sequencing studies revealed microhomologies at the junctures of the der(8) and idic(21) in the half-aunt, suggesting a replicative mechanism in the rearrangement formation. Furthermore, interstitial telomeric sequences (ITS) were identified in the juncture between chromosomes 8 and 21 in the der(8). CONCLUSION: Mosaicism in the proband, his half-sister and half-cousin resulting from loss of chromosome 21 material from the der(8) appears to be a postzygotic event due to the genomic instability of ITS and associated with selective growth advantage of normal cells. The reversion of the inherited der(8) to a normal chromosome 8 in this family resembles revertant mosaicism of point mutations. We propose that ITS could mediate recurring revertant mosaicism for some constitutional chromosomal structural abnormalities.

B-Cell Acute Lymphoblastic Leukemia with iAMP21 in a Patient with Constitutional Ring Chromosome 21.

Pediatric B-cell acute lymphoblastic leukemia (B-ALL) is associated with various specific cytogenetic and molecular markers that significantly influence treatment and prognosis. Intrachromosomal amplification of chromosome 21 (iAMP21) defines a rare distinct cytogenetic subgroup of childhood B-ALL, which is characterized by amplification of region 21q22.12 comprising the RUNX1 gene. Constitutional structural chromosomal abnormalities involving chromosome 21 confer an increased risk for B-ALL with iAMP21. Here, we report the development of B-ALL with iAMP21 in a 9-year-old child with a constitutional ring chromosome 21, r(21)c, uncovered after B-ALL diagnosis. Cytogenetic and microarray analysis of the post-therapy sample revealed an abnormal chromosome 21 lacking a satellite and having a deletion of the terminal 22q22.3 region, consistent with a constitutional ring chromosome 21, r(21)(p11.2q22). On a retrospective analysis, this ring chromosome was observed in the normal cells in the pre-treatment diagnostic specimen. Constitutional ring chromosome 21 may remain undetected in patients with mild or no neurodevelopmental phenotype, posing an unknown lifelong risk of developing B-ALL with iAMP21. Individuals with constitutional structural chromosome 21 rearrangements such as ring 21 require a close surveillance and long-term follow-up studies to establish their risk of B-ALL relapse and possibility of developing other malignancies. Germline analysis is recommended to all pediatric patients with iAMP21-related B-ALL to rule out structural chromosome 21 rearrangements and to elucidate molecular mechanisms of iAMP21 formation.

Cytogenetic and molecular characterization of a patient having infertility and mild intellectual disability with a very rare unstable ring chromosome 13.

INTRODUCTION: Ring chromosomes arise from breakage and fusion at distal regions of short and long arms of the chromosomes. The effect of the ring chromosome on the phenotype may vary widely depending on the amount of the deletion in the chromosomal areas and genes implicated in these regions. CASE PRESENTATION: We present a 35-year-old male patient with infertility and mild intellectual disability (MID) who has de novo ring 13 (r(13)) chromosomes. To determine chromosomal abnormality, we performed karyotype analysis, Y chromosome microdeletion analysis, FISH, and aCGH techniques. CONCLUSION: The patient's karyotype analysis result was mos46,XY,r(13)(p13q34)[75]/45,XY,-13[14]/46,XY,dic (13;13)[8]/47,XY,r(13), + r(13)[2]/46,XY,tetrac r(13;13;13;13)[1]. FISH analysis supported the findings of the cytogenetic analysis. Y microdeletion analysis showed that the AZF region was intact. On aCGH analysis, we detected a 1.5 megabase deletion at the end of chromosome 13, including the CHAMP1 gene. The loss of the CHAMP1 gene, in particular, may explain our patient's MID, and the other deleted genes at 13q34 may explain our patient's infertility.