Detection of hallmark genomic aberrations in acute myeloid leukemia (AML) is essential for diagnostic subtyping, prognosis and patient management. However, cytogenetic/cytogenomic techniques used to identify those aberrations, such as karyotyping, fluorescence in situ hybridization (FISH) or chromosomal microarray analysis (CMA), are limited by the need for skilled personnel as well as significant time, cost and labor. Optical genome mapping (OGM) provides in a single, cost-effective assay significantly higher resolution than karyotyping with comprehensive genome-wide analysis comparable to CMA and the added unique ability to detect balanced structural variants (SVs). Here, we report in a real-world setting the performance of OGM in a cohort of 100 AML cases, which were previously characterized by karyotype alone or karyotype and FISH or CMA. OGM identified all clinically relevant SVs and copy number variants (CNVs) reported by these standard cytogenetic methods when representative clones were present in >5% allelic fraction. Importantly, OGM identified clinically relevant information in 13% of cases that had been missed by the routine methods. Three cases reported with normal karyotypes were shown to have cryptic translocations involving gene fusions. In 4% of cases, OGM findings would have altered recommended clinical management and in an additional 8%, OGM would have rendered the cases potentially eligible for clinical trials. The results from this multi-institutional study indicate that OGM effectively recovers clinically relevant SVs and CNVs found by standard of care methods and reveals additional SVs not reported. Furthermore, OGM minimizes the need for labor-intensive multiple cytogenetic tests while concomitantly maximizing diagnostic detection through a standardized workflow.

Detection of hallmark genomic aberrations in acute myeloid leukemia (AML) is essential for prognosis and patient management. Clinical practice guidelines for identifying such structural variants (SVs), established by the World Health Organization (WHO), European Leukemia Net (ELN) and National Comprehensive Cancer Network (NCCN), rely substantially on cytogenetic/cytogenomic techniques such as karyotyping, fluorescence in situ hybridization (FISH) or chromosomal microarray analysis (CMA). However, these techniques are limited by the need for skilled personnel as well as significant time and labor, making them cost-prohibitive for some patients. Optical genome mapping (OGM) addresses these limitations and allows for the accurate identification of clinically significant SVs using a novel, high throughput, inexpensive methodology. In a single assay, OGM offers a significantly higher resolution than karyotyping with comprehensive genome-wide analysis comparable to CMA and the added unique ability to detect balanced SVs that are missed by microarray. Here, we report the performance of OGM in a cohort of 100 AML cases, which were previously characterized by karyotype alone or karyotype and FISH. CMA was performed as an additional test in some cases. OGM identified all the clinically relevant SVs and CNVs reported by these standard cytogenetic methods. Moreover, OGM identified clinically relevant SVs in 11% of cases that had been missed by the routine methods. In 24% of cases, OGM refined the underlying genomic structure reported by traditional cytogenomic testing (13%), identified additional clinically relevant variants (7%) or both (4%). Three of 48 (6.25%) cases reported with normal karyotypes were shown to have cryptic translocations involving gene fusions. Two of these cases included fusion between NSD1-NUP98. Based on the comprehensive genomic profiling of the AML patients in this multi-institutional study, we recommend that OGM be considered as a first-line test for detection and identification of clinically relevant SVs.

Chromosomal aberrations are associated with increased cancer risk in adults. Previously, we demonstrated that stable aberrations involving chromosomes 1-6 in cord blood are associated with prenatal exposure to polycyclic aromatic hydrocarbons (PAHs) measured in air and are disproportionate to genomic content. We now examine whether the association with air PAHs is chromosome-specific and extends to smaller chromosomes. Using Whole Chromosome Paints for chromosomes 1-6, 11,12,14,19, and a 6q sub-telomere specific probe, we scored 48 cord bloods (1500 metaphases per sample) from newborns monitored prenatally for airborne PAH exposure in the Columbia Center for Children’s Environmental Health cohort. Frequencies of stable aberrations were calculated as incident aberrations per 100 Cell Equivalents scored, and examined for association with airborne PAHs. Aberrations in chromosome 6 occurred more frequently than predicted by genomic content (p<0.008). Levels of both prenatal airborne PAHs and stable aberration frequency in chromosomes 1-6 decreased to half the levels reported previously in the same cohort (mean PAH decreased from 3.6 to 1.8 ng/m3; mean stable aberration frequency from 0.56 to 0.24, SD=0.19). The mean stable aberration frequency was 0.45 (SD=0.15) in chromosomes 11-19. After adjusting for gender, ethnicity, and household smokers, the mean stable aberration frequency increased with increasing PAH exposure: with a doubling of prenatal PAH exposure, the mean stable aberration frequency for the chromosome1-6 group increased by a factor of 1.49 (95%CI: 0.84, 2.66; p=0.17); for chromosomes 11-19 mean stable aberration frequency increased by 2.00 (95%CI:1.11, 3.62; p=0.02); for chromosome 6 alone, it increased by 3.16 (95%CI: 0.93,10.77; p= 0.06); there was no increase for chromosomes1-5 (p>0.8). Aberrations in chromosomes 11,12,14,19 and 6 were associated with prenatal exposure to PAHs in air, even at lower levels of PAH in air. The observed chromosome-specific effects of prenatal airborne PAHs raise concern about potential cancer risk.

Although monosomy X is the most common karyotype in patients with Turner syndrome, the presence of Y chromosome material has been observed in about 10% of patients. Y chromosome material in patients with Turner syndrome poses an increased risk of gonadoblastoma and malignant transformation. We report a woman with a diagnosis of Turner syndrome at 12 years of age, without signs of virilization, and karyotype reported as 46,X,del(X)(q13). At 26 years, cytogenetic studies indicated the patient to be mosaic for monosomy X and a cell line that contained a du­plicated Yq chromosome. Bilateral gonadectomy was performed and revealed streak gonads, without evidence of gonadoblastoma. Histological analysis showed ovarian stromal cells with few primordial tubal structures. FISH performed on streak gonadal tissue showed a heterogeneous distribution of SRY, with exclusive localization to the primordial tubal structures. DNA extraction from the gonadal tissue showed a 6.5% prevalence of SRY by microarray analysis, contrasting the 86% prevalence in the peripheral blood sample. This indicates that the overall gonadal sex appears to be determined by the majority gonosome complement in gonadal tissue in cases of sex chromosome mosaicism. This case also raises questions regarding malignancy risk associated with Y prevalence and tubal structures in gonadal tissue.

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