11q13.3q13.4 deletion plus 9q21.13q21.33 duplication in an affected girl arising from a familial four-way balanced chromosomal translocation

Optical Genome Mapping for Chromosomal Aberrations Detection-False-Negative Results and Contributing Factors

Optical genome mapping (OGM) has been known as an all-in-one technology for chromosomal aberration detection. However, there are also aberrations beyond the detection range of OGM. This study aimed to report the aberrations missed by OGM and analyze the contributing factors. OGM was performed by taking both GRCh37 and GRCh38 as reference genomes. The OGM results were analyzed in blinded fashion and compared to standard assays. Quality control (QC) metrics, sample types, reference genome, effective coverage and classes and locations of aberrations were then analyzed. In total, 154 clinically reported variations from 123 samples were investigated. OGM failed to detect 10 (6.5%, 10/154) aberrations with GRCh37 assembly, including five copy number variations (CNVs), two submicroscopic balanced translocations, two pericentric inversion and one isochromosome (mosaicism). All the samples passed pre-analytical and analytical QC. With GRCh38 assembly, the false-negative rate of OGM fell to 4.5% (7/154). The breakpoints of the CNVs, balanced translocations and inversions undetected by OGM were located in segmental duplication (SD) regions or regions with no DLE-1 label. In conclusion, besides variations with centromeric breakpoints, structural variations (SVs) with breakpoints located in large repetitive sequences may also be missed by OGM. GRCh38 is recommended as the reference genome when OGM is performed. Our results highlight the necessity of fully understanding the detection range and limitation of OGM in clinical practice.

Confusing finding of quantitative fluorescent polymerase chain reaction analysis in invasive prenatal genetic diagnosis: A case report

BACKGROUND

Quantitative fluorescent polymerase chain reaction (QF-PCR) is a rapid prenatal diagnostic method for abnormalities on chromosomes 21, 18, and 13 and sex chromosomal aneuploidy. However, the value of QF-PCR in diagnosing chromosomal structural abnormalities is limited. In this article, we report a confusing QF-PCR finding in a pregnant woman who underwent amniocentesis.

CASE SUMMARY

The short tandem repeat marker AMXY (Xp22.2/Yp11.2) located on the sex chromosome exhibited a trisomic biallelic pattern, indicating that the karyotype of the fetus might be 47,XYY. Chromosome analysis performed on cultured amniocytes showed a normal male karyotype of the fetus. Copy number variation sequencing confirmed a 500 kb duplication at Yp11.2-Yp11.2 (chrY:6610001_ 7110000) and a 250 kb duplication at Yp11.2-Yp11.2 (chrY:7110001_7360000).

CONCLUSION

In conclusion, the comprehensive application of different methods could achieve a higher detection rate and accuracy for the prenatal diagnosis of chromosomal disorders through chromosomal testing.