#152 : Exploring the Limitations of Linkage-Only PGT-M

Abstract

Background and Aims: Although PGT-M cases can be conducted using linkage only, the inclusion of a direct test targeting the relevant genetic variants should be fundamental to best practise. We present four cases illustrating the limitations of linkage only PGT-M. Methods: Three cases used STRs for linkage analysis and the fourth Illumina Infinium Karyomapping. Direct variant detection encompassed Sanger sequencing, STRs and/or fragment PCR. Results: Case 1 Osteoporosis-pseudoglioma syndrome Sanger sequencing for LRP5c.3107G[Formula: see text]A and LRP5c.4487C[Formula: see text]A were critical for identifying a recombination in the familial control and subsequent correct assignment of STR phasing. Case 2 Osteogenesis imperfecta type I SNP-based linkage identified a recombinant embryo. Sanger sequencing for COL1A1c.2461G[Formula: see text]A resolved an unknown status to affected. Case 3 Neurofibromatosis type II Variant detection in this de novo mosaic case used two STRs within the NF2 exon2-11del to establish low- and high-risk linkage patterns. Two tumour samples with different second hit mutations exhibited reduced signal intensity for one allele. This was consistent with the presence of a weaker deleted allele due to sample contamination with non-tumour cells. Four of nine embryos contained two alleles within the minimum deletion and were first choice for transfer, resulting in an NAD prenatal confirmation and healthy liveborn. Case 4 Neurofibromatosis type I A de novo mosaic case required reverse linkage by means of a direct assay for the NF1c.1445_1446insCC variant. Affected embryos were subsequently used to phase flanking STRs and obtain linkage, resulting in one liveborn and one ongoing pregnancy. Conclusions: When a direct test is not included in PGT-M, a family may not be able to be offered a test, or misdiagnosis risk may increase. For de novo, mosaic and cases with suspected recombination in a reference sample, analysis of multiple cycles and/or the inclusion of non-clinical embryos to increase sample numbers improves accuracy of testing.