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ABSTRACT Background X‐linked recessive type 3 Charcot–Marie–Tooth (CMTX3) is a rare subtype of childhood‐onset CMT. To date, all reported CMTX3 patients share a common founder 78 kb insertion from chromosome 8 into the Xq27.1 palindrome region. Methods We conducted patient–parent trio optical genome mapping (OGM) on a male patient presenting with clinically diagnosed Dejerine–Sottas disease for whom initial standard diagnostic genetic tests, including whole‐genome sequencing (WGS), yielded negative results. Results OGM analysis revealed a maternally inherited interchromosomal insertion from chromosome region 7q31.1 into Xq27.1. Coupled with manual reassessment of WGS data, this confirmed the molecular diagnosis of atypical CMTX3 and showed that the 122.4 kb inserted fragment contained DLD and partially LAMB1. Subsequent analyses confirmed that the rearrangement had arisen de novo in the proband's mother. Conclusion We report the second Xq27.1 rearrangement associated with CMTX3, providing novel clinical insights into its phenotypic and genotypic spectrum. Our findings highlight the importance of including genomic rearrangement analysis of Xq27.1 in standard diagnostic pipelines for childhood‐onset CMT. Given the overlap in polyneuropathy phenotypes resulting from insertions from chromosomes 7 and 8 into the same Xq27.1 palindrome region, the pathogenic mechanism underlying peripheral neuropathy in CMTX3 likely involves dysregulation of genes within this region.

Abstract Background Despite recent advances in prenatal genetic diagnosis, medical geneticists still face considerable difficulty in interpreting the clinical outcome of copy‐number‐variant duplications and defining the mechanisms underlying the formation of certain chromosomal rearrangements. Optical genome mapping (OGM) is an emerging cytogenomic tool with proved ability to identify the full spectrum of cytogenetic aberrations. Methods Here, we report on the use of OGM in a prenatal diagnosis setting. Detailed breakpoint mapping was used to determine the relative orientations of triplicated and duplicated segments in two unrelated foetuses harbouring chromosomal aberrations: a de novo 15q23q24.2 triplication and a paternally inherited 13q14.2 duplication that overlapped partially with the RB1 gene. Results OGM enabled us to suggest a plausible mechanism for the triplication and confirmed that the RB1 duplication was direct oriented and in tandem. This enabled us to predict the pathogenic consequences, refine the prognosis and adapt the follow‐up and familial screening appropriately. Conclusion Along with an increase in diagnostic rates, OGM can rapidly highlight genotype–phenotype correlations, improve genetic counselling and significantly influence prenatal management.

Abstract Familial adult myoclonic epilepsy (FAME) is an adult‐onset neurological disease characterized by cortical tremor, myoclonus, and seizures due to a pentanucleotide repeat expansion: a combination of pathogenic TTTCA expansion associated with a TTTTA repeat in introns of six different genes. Repeat‐primed PCR (RP‐PCR) is an inexpensive test for expansions at known loci. The analysis of the SAMD12 locus revealed that the repeats have different size, configuration, and composition. The TTTCA repeats can be very long (>1000 repeats) but also very short (14 being the shortest identified). Here, we report siblings of European descent with the clinical diagnosis of FAME yet a negative RP‐PCR test. Using short‐read genome sequencing, we identified the pentanucleotide expansion in intron 4 of SAMD12, which was confirmed by CRIPSR‐Cas9‐mediated enrichment and long‐read sequencing to be of (TTTTA)~879(TTTCA)3(TTTTA)7(TTTCA)7 configuration. Our finding is the first to associate the SAMD12 locus in European patients with FAME and currently represents the shortest identified TTTCA expansion. Our results suggest that the SAMD12 locus should be tested in patients with suspected FAME independent of ethnicity. Furthermore, RP‐PCR may miss the underlying mutation, and genome sequencing may be needed to confirm the pathogenic repeat.

Abstract Background We describe a 13‐year‐old girl with a 11q13.3q13.4 deletion encompassing the SHANK2 gene and a 9q21.13q21.33 duplication. She presented with pre‐ and postnatal growth retardation, global developmental delay, severe language delay, cardiac abnormalities, and dysmorphisms. Her maternal family members all had histories of reproductive problems. Methods Maternal family members with histories of reproductive problems were studied using G‐banded karyotyping and optical genome mapping (OGM). Long‐range PCR (LR‐PCR) and Sanger sequencing were used to confirm the precise break point sequences obtained by OGM. Results G‐banded karyotyping characterized the cytogenetic results as 46,XX,der(9)?del(9)(q21q22)t(9;14)(q22;q24),der(11)ins(11;?9)(q13;?q21q22),der(14)t(9;14). Using OGM, we determined that asymptomatic female family members with reproductive problems were carriers of a four‐way balanced chromosome translocation. Their karyotype results were further refined as 46,XX,der(9)del(9)(q21.13q21.33)t(9;14)(q21.33;q22.31),der(11)del(11)(q13.3q13.4)ins(11;9)(q13.3;q21.33q21.13),der(14)t(9:14)ins(14;11)(q23.1;q13.4q13.3). Thus, we confirmed that the affected girl inherited the maternally derived chromosome 11. Furthermore, using LR‐PCR, we showed that three disease‐related genes (TMC1, NTRK2, and KIAA0586) were disrupted by the breakpoints. Conclusions Our case highlights the importance of timely parental origin testing for patients with rare copy number variations, as well as the accurate characterization of balanced chromosomal rearrangements in families with reproductive problems. In addition, our case demonstrates that OGM is a useful clinical application for analyzing complex structural variations within the human genome.

Abstract Background Balanced reciprocal translocation is one of the most common chromosomal abnormalities in humans that may lead to infertility, recurrent pregnancy loss, or having children with physical or mental abnormalities. Karyotyping and FISH are traditional detection approaches with a low resolution. Bionano optical genome mapping (OGM) developed in recent years can be used to analyze chromosomal abnormalities at a higher resolution, providing the possibility of more in‐depth analyses of balanced chromosome translocations. Methods To evaluate the feasibility of OGM to detect chromosome balanced translocations, 10 genetic outpatients were collected and detected simultaneously by karyotype analysis, FISH, CNV‐seq, and Bionano OGM in this study. Results The results showed that the karyotypes of the patients were detected by karyotype analysis, FISH, and Bionano OGM, but one patient with karyotype t(Y,19) was not correctly detected by OGM. There were not find any chromosome abnormality by CNV‐seq. More importantly, OGM allowed the location of the mutation to the gene level, which is important for aiding diagnoses, compared to karyotype analysis, and FISH. Conclusions This study shows that OGM can be a high adjunctive diagnostic method for detecting balanced chromosome translocations, but the accuracy and precision of OGM detecting mutations need to be gradually improved in telomere and centromere regions.

ABSTRACT Background Currently available structural variant (SV) detection methods do not span the complete spectrum of disease‐causing SVs. Optical genome mapping (OGM), an emerging technology with the potential to resolve diagnostic dilemmas, was performed to investigate clinically‐relevant SVs in a 4‐year‐old male with an epileptic encephalopathy of undiagnosed molecular origin. Methods OGM was utilized to image long, megabase‐size DNA molecules, fluorescently labeled at specific sequence motifs throughout the genome with high sensitivity for detection of SVs greater than 500 bp in size. OGM results were confirmed in a CLIA‐certified laboratory via mate‐pair sequencing. Results OGM identified a mosaic, de novo 90 kb deletion and inversion on the X chromosome disrupting the CDKL5 gene. Detection of the mosaic deletion, which had been previously undetected by chromosomal microarray, an infantile epilepsy panel including exon‐level microarray for CDKL5, exome sequencing as well as genome sequencing, resulted in a diagnosis of X‐linked dominant early infantile epileptic encephalopathy‐2. Conclusion OGM affords an effective technology for the detection of SVs, especially those that are mosaic, since these remain difficult to detect with current NGS technologies and with conventional chromosomal microarrays. Further research in undiagnosed populations with OGM is warranted.

Introduction: Chromosomal aberrations are the most important etiological factors for birth defects. Optical genome mapping is a novel cytogenetic tool for detecting a broad range of chromosomal aberrations in a single assay, but relevant clinical feasibility studies of optical genome mapping in prenatal diagnosis are limited., Material and Methods: We retrospectively performed optical genome mapping analysis of amniotic fluid samples from 34 fetuses with various clinical indications and chromosomal aberrations detected through standard-of-care technologies, including karyotyping, fluorescence in situ hybridization, and/or chromosomal microarray analysis., Results: In total, we analyzed 46 chromosomal aberrations from 34 amniotic fluid samples, including 5 aneuploidies, 10 large copy number variations, 27 microdeletions/microduplications, 2 translocations, 1 isochromosome, and 1 region of homozygosity. Overall, 45 chromosomal aberrations could be confirmed by our customized analysis strategy. Optical genome mapping reached 97.8% concordant clinical diagnosis with standard-of-care methods for all chromosomal aberrations in a blinded fashion. Compared with the widely used chromosomal microarray analysis, optical genome mapping additionally determined the relative orientation and position of repetitive segments for seven cases with duplications or triplications. The additional information provided by optical genome mapping will be conducive to characterizing complex chromosomal rearrangements and allowing us to propose mechanisms to explain rearrangements and predict the genetic recurrence risk., Conclusions: Our study highlights that optical genome mapping can provide comprehensive and accurate information on chromosomal aberrations in a single test, suggesting that optical genome mapping has the potential to become a promising cytogenetic tool for prenatal diagnosis., (© 2023 The Authors. Acta Obstetricia et Gynecologica Scandinavica published by John Wiley & Sons Ltd on behalf of Nordic Federation of Societies of Obstetrics and Gynecology (NFOG).)