This study describes a successful case of preimplantation genetic testing for the monogenic disease (PGT-M) of methylmalonic acidemia (MMA). To avoid the transmission of pathogenic mutations and unnecessary pregnancy termination we applied next-generation sequencing (NGS)-based haplotyping on a couple with a previously deceased MMA offspring. After embryo preparation, all samples were amplified successfully by whole genome amplification. We performed preimplantation genetic testing for aneuploidy (PGT-A) to determine the copy number of embryos' chromosomes. PGT-A results showed five blastocysts (2, 11, 14, 15 and 16) with balanced chromosomes (46, XN). Two techniques were used for PGT-M. Sanger sequencing was used to detect the mutations of MMUT gene directly, and NGS-based single nucleotide polymorphism (SNP) haplotyping was used to distinguish the chromosomes that carried the mutation. Sanger sequencing and NGS-based SNP haplotyping confirmed that samples 2 and 15 carried c.730insTT, samples 11 and 15 carried c.1105 C > T and samples 14 and 16 did not carry any mutation. Thus, blastocyst 14 was transferred into the mother's uterus. After prenatal diagnosis at 18 weeks of gestation, a healthy infant without MMUT mutation was born at full term. This study highlights the efficiency of NGS-based SNP haplotyping for PGT-M of MMA.Abbreviations: MMA: methylmalonic acidemia; MMUT: methylmalonyl-CoA mutase; PGT-M: preimplantation genetic testing for monogenic disease; PGD: preimplantation genetic diagnosis; IVF: in vitro fertilization; ADO: allele dropout; WGA: whole genome amplification; SNP: single nucleotide polymorphism; NGS: next-generation sequencing; PND: prenatal diagnosis; ICSI: intracytoplasmic sperm injection; TE: trophectoderm; DOP-PCR: degenerate oligonucleotide primed polymerase chain reaction; PGT-A: preimplantation genetic testing for aneuploidy; PCR: polymerase chain reaction.
Keywords: Preimplantation genetic testing; haplotyping; methylmalonic acidemia; next-generation sequencing; prenatal diagnosis.