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Purpose: Klinefelter syndrome, a sex chromosome aneuploidy (SCA), is associated with a 47,XXY chromosomal complement and is diagnosed in ∼1:600 live male births. Individuals with a 46,XX cell line, in addition to 47,XXY, are less common with a limited number of published case reports., Methodology: To better understand the implications of a 47,XXY/46,XX karyotype, we conducted a retrospective, multicenter analysis of the cytogenetic findings and associated clinical records of 34 patients diagnosed with this SCA across 14 institutions., Results: Presence of the XX cell line ranged from 5% to 98% in patient specimens. Phenotypes also exhibited significant heterogeneity with some reporting a single reason for referral and others presenting with a constellation of symptoms, including ambiguous genitalia and ovotestes. Ovotestes were present in 12% of individuals in this cohort, who had a significantly higher percentage of XX cells. Notably, 2 patients were assigned female sex at birth., Conclusion: These findings highlight the variability of the clinical phenotypes associated with this SCA, as well as the challenges of clinical management for this population. Karyotype or fluorescence in situ hybridization analysis, which offer single-cell resolution, rather than chromosomal microarray or molecular testing, is the ideal test strategy in these instances as mosaicism can occur at low levels., Competing Interests: Conflict of Interest The authors have no conflicts of interest to declare., (Copyright © 2024 American College of Medical Genetics and Genomics. Published by Elsevier Inc. All rights reserved.)

Genome sequencing (GS) is a powerful clinical tool used for the comprehensive diagnosis of germline disorders. GS library preparation typically involves mechanical DNA fragmentation, end repair, and bead-based library size selection followed by adapter ligation, which can require a large amount of input genomic DNA. Tagmentation using bead-linked transposomes can simplify the library preparation process and reduce the DNA input requirement. Here we describe the clinical validation of tagmentation-based PCR-free GS as a clinical test for rare germline disorders. Compared with the Genome-in-a-Bottle Consortium benchmark variant sets, GS had a recall >99.7% and a precision of 99.8% for single nucleotide variants and small insertion-deletions. GS also exhibited 100% sensitivity for clinically reported sequence variants and the copy number variants examined. Furthermore, GS detected mitochondrial sequence variants above 5% heteroplasmy and showed reliable detection of disease-relevant repeat expansions and SMN1 homozygous loss. Our results indicate that while lowering DNA input requirements and reducing library preparation time, GS enables uniform coverage across the genome as well as robust detection of various types of genetic alterations. With the advantage of comprehensive profiling of multiple types of genetic alterations, GS is positioned as an ideal first-tier diagnostic test for germline disorders., (Copyright © 2023 Association for Molecular Pathology and American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Genome-wide copy number profiling by single-nucleotide polymorphism (SNP) array is increasingly employed in the clinical diagnostic workup of melanocytic tumors. We present our SNP array results on 675 melanocytic tumors, including 615 histologically ambiguous tumors evaluated by our institution's dermatopathology consultation service and a separate validation cohort of 26 known benign nevi and 34 known malignant melanomas. The total number of somatic copy number abnormalities, sub-chromosomal copy number abnormalities, regions of homozygosity, and abnormalities at disease-associated regions was significantly associated with a diagnosis of malignancy across disease categories. In our study, the number of copy number abnormalities was the factor that best discriminated between benign versus malignant diagnoses, confirming recent published research. Histologically ambiguous tumors had a range and spectrum of abnormalities, including recurrent 11p gains, copy state transitions over kinase genes, and 3p deletions overlapping BAP1 in neoplasms with Spitzoid morphology. Our data suggest that histologically ambiguous melanocytic neoplasms and early primary melanomas have a range of abnormalities that is intermediate between unambiguous benign or malignant melanocytic neoplasms. Careful technical review and an integrated diagnostic approach are essential for the accurate interpretation of SNP array results on histologically ambiguous melanocytic tumors., (Copyright © 2022 Association for Molecular Pathology and American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Purpose: Copy-number variants (CNVs) of uncertain clinical significance are routinely reported in a clinical setting only when exceeding predetermined reporting thresholds, typically based on CNV size. Given that very few genes are associated with triplosensitive phenotypes, it is not surprising that many interstitial duplications <1 Mb are found to be inherited and anticipated to be of limited or no clinical significance., Methods: In an effort to further refine our reporting criteria to maximize diagnostic yield while minimizing the return of uncertain variants, we performed a retrospective analysis of all clinical microarray cases reported in a 10-year window. A total of 1112 reported duplications had parental follow-up, and these were compared by size, RefSeq gene content, and inheritance pattern. De novo origin was used as a rough proxy for pathogenicity., Results: Approximately 6% of duplications 500 kb-1 Mb were de novo observations, compared with approximately 14% for 1-2 Mb duplications (p = 0.0005). On average, de novo duplications had higher gene counts than inherited duplications., Conclusion: Our data reveal limited diagnostic utility for duplications of uncertain significance <1 Mb. Considerations for revised reporting criteria are discussed and are applicable to CNVs detected by any genome-wide exploratory methodology, including exome/genome sequencing.

Mate-pair sequencing (MPseq), using long-insert, paired-end genomic libraries, is a powerful next-generation sequencing-based approach for the detection of genomic structural variants. SVAtools is a set of algorithms to detect both chromosomal rearrangements and large (>10 kb) copy number variants (CNVs) in genome-wide MPseq data. SVAtools can also predict gene disruptions and gene fusions, and characterize the genomic structure of complex rearrangements. To illustrate the power of SVAtools' junction detection methods to provide comprehensive molecular karyotypes, MPseq data were compared against a set of samples previously characterized by traditional cytogenetic methods. Karyotype, FISH and chromosomal microarray (CMA), performed for 29 patients in a clinical laboratory setting, collectively revealed 285 breakpoints in 87 rearrangements. The junction detection methods of SVAtools detected 87% of these breakpoints compared to 48%, 42% and 57% for karyotype, FISH and CMA respectively. Breakpoint resolution was also reported to 1 kb or less and additional genomic rearrangement complexities not appreciable by standard cytogenetic techniques were revealed. For example, 63% of CNVs detected by CMA were shown by SVAtools' junction detection to occur secondary to a rearrangement other than a simple deletion or tandem duplication. SVAtools with MPseq provides comprehensive and accurate whole-genome junction detection with improved breakpoint resolution, compared to karyotype, FISH, and CMA combined. This approach to molecular karyotyping offers considerable diagnostic potential for the simultaneous detection of both novel and recurrent genomic rearrangements in hereditary and neoplastic disorders., (Copyright © 2017 Elsevier Inc. All rights reserved.)