Preimplantation Genetic Testing in a Family with Neurofibromatosis Type 1

Neurofibromatosis is an autosomal dominant genetic disease caused by the abnormal development of neural crests due to genetic defects and is difficult to treat. Patients have a characteristic phenotype with neurofibromas as the main features in different forms, which are accompanied by multisystem involvement. The clinical symptoms of this disease vary greatly, making the treatment more difficult. Preimplantation genetic testing (PGT) is a useful technique to prevent chromosomal aneuploidies and other genetic disorders in origin. PGT for monogenic diseases (PGT-M) is now widely used as an effective strategy to screen embryos for monogenic or chromosomal diseases before implantation. In this study, PGT-M was performed in a family history of hereditary with neurofibromatosis type 1 (NF1) to prevent the offspring from inheriting disease-causing gene variant from their parents. Trio-based whole-exome sequencing was used to identify potential pathogenic variants associated with NF1. Blastocyst biopsy was performed on embryos obtained by intracytoplasmic sperm injection. Single-cell amplification of biopsied cells was performed for targeted next-generation sequencing. Single nucleotide polymorphism markers on both sides of NF1 were selected to identify disease-carrying haplotypes in each embryo. A novel heterozygotic frameshift pathogenic variant, c.2033_2034delinsA(p.P678Qfs*10), was identified in the NF1 gene in the proband. A total of five blastocysts were biopsied, and the PGT results showed that only one blastocyst was unaffected and was euploid, and the remaining four blastocysts were all carrying paternal pathogenic variants. The only one normal blastocyst was transferred in a frozen-thawed embryo transfer cycle, and a live singleton pregnancy was successfully achieved. At 18 weeks, the amniocentesis test revealed normal karyotype, and the variant carried by the proband was not detected. At 40 weeks, the proband's wife successfully delivered a healthy baby naturally. PGT is an effective method to detect chromosome copy number variation and gene variant sites in embryos, and it provides suggestions for possible innovations to block the transmission of single-gene genetic diseases to offspring, thereby preventing the occurrence of birth defects.