Preimplantation genetic testing for mucopolysaccharidosis type II: a case report

Aim: description of an assisted reproductive technology (ART) program with preimplantation genetic testing (PGT) for spinocerebellar ataxia type 1 (SCA1) in combination with preimplantation chromosome analysis. Methods. Planning and implementation of PGT was performed for a couple (aged 30 and 31) from Sakha (Yakutia) at risk of SCA1. We have developed PGT system for monogenic diseases (PGT-M), which includes the analysis of the pathogenic variant of the ATXN1 gene (NM_000332.3(ATXN1):c.589_591CAG(36_38) (p.Gln208_His209ins(Gln)n) and polymorphic STR markers linked to the gene. For setup study DNA was isolated from the blood of the patient and partner, the patient’s sister and father, and a healthy unrelated donor. The study was performed by nested PCR with detection by fragment analysis. The developed system was validated on single cell samples. Ovulation stimulation and embryological procedures during the ART program were performed according to standard protocols, fertilization was performed by ICSI. Embryo biopsy was performed on the 5th day of development. Whole genome amplification (WGA) for trophectoderm samples was performed using multiple displacement amplification (MDA). WGA product was used for PGT-M according to the system developed at the setup stage, then for chromosomal microarray analysis of aneuploidy (PGT-A). The cryotransfer was performed taking into account the results of preimplantation testing. Results. The developed PGT-M system included analysis of the ATXN1 gene fragment carrying CAG repeats and analysis of 9 informative STR markers flanking the gene. Five mature oocytes were obtained in the ART program. Three embryos reached the blastocyst stage and were biopsied; WGA and PGT-M were performed for them. The mutant allele was well identified in two embryos. One of the three embryos was determined to be normal for the ATXN1 genotype and maternal STR haplotype. PGT-A was performed for one normal embryo, the result showed a normal chromosomal status. The embryo was transferred into the uterus. The results of hCG (human chorionic gonadotropin) confirmed the implantation of the embryo. Conclusions. Our clinical case demonstrates the successful implementation of the ART program with PGT-M for SCA1 in combination with the analysis of PGT-A.

PGT-M, Preimplantation testing for monogenic/single gene defects, spinocerebellar ataxia type 1, PGT-A, ART, ATXN1 gene

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