Identification of a Novel NF1 Frameshift Variant in a Chinese Family with Neurofibromatosis Type 1

Preimplantation Genetic Testing in a Family with Neurofibromatosis Type 1

Background: 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. Methods: 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. Results: 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. Conclusion: 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.

Identifying a novel frameshift pathogenic variant in a Chinese family with neurofibromatosis type 1 and review of literature

AIM

To detect the pathogenic gene variant in a family with neurofibromatosis type 1 (NF1).

METHODS

This patient with NF1 was sequenced using target sequence capture and high-throughput sequencing technology. After detecting the suspicious pathogenic variant type, the pathogenic variant sites of the patient and the patient's family members were verified by multiple ligation dependent probe amplification and Sanger sequencing. Sift, polyphen-2, Mutation Taster and GERP++ software were used to predict the pathogenicity of the unknown loci. The clinical data, diagnosis and treatment process of the patients were reviewed. Using the keyword "NF1; frameshift pathogenic variant", relevant literature was gathered for analysis from Chinese and international databases, with articles dating from the establishment of each database to April 2022.

RESULTS

A heterozygous frameshift pathogenic variant of NF1 in exon 33 was detected in the patient. The insertion of adenine in coding region 4486 resulted in the replacement of isoleucine with asparagine in protein 1497. Sanger sequencing validation and segregation analysis were performed, which demonstrated that the NF1 gene was cosegregated with the disease phenotype in this family. This study identified a novel NF1 heterozygous frameshift mutation c.4486dupA (p.I1497Nfs*12). Relevant literature retrieval found 7 Chinese articles and 12 foreign articles. With NF1 gene mutation, mutation types are diverse, including point mutation, frameshift mutation, splice site mutation, exon mutation, chimeric mutation and de novo mutation. Foreign reports are based on autosomal dominant inheritance.

CONCLUSION

This study's results demonstrate that a novel deletion in exon 33 caused NF1 in this Chinese family, expanding the mutational spectrum of the NF1 gene.

Somatostatinoma: Beyond neurofibromatosis type 1 (Review)

Somatostatinoma is a tumour mainly originating from pancreas or duodenum; overall with an incidence of 1/40 million persons. We introduce a narrative review of literature of somatostatinoma including the relationship with neurofibromatosis type 1. Clinical presentation includes: Diabetes mellitus, cholelithiasis, steatorrhea, abdominal pain, and obstructive jaundice while papillary tumour may cause acute pancreatitis. The neoplasia may develop completely asymptomatic or it is detected as an incidental finding during an imaging or a surgical procedure. It may be sporadic or associated to genetic backgrounds especially for duodenal localisation as neurofibromatosis type 1 (NF1 gene with malfunction of RAS/MAPK pathway) or Pacak-Zhuang syndrome (EPAS1 gene encoding HIF). Surgery represents the central approach if feasible but the prognostic depends on location, and grading as indicated by WHO 2017 classification of neuroendocrine tumours. Previously known as Von Recklinghausen disease, neurofibromatosis type 1, the most frequent neurocutaneous syndrome, is an autosomal dominant disorder including: Café-au-lait spot, skin fold freckling on flexural zones, and neurofibromas as well as tumours such as gliomas of optic nerve, gastrointestinal stromal tumours (GISTs), iris hamartomas and brain tumours. Duodenal somatostatinoma is associated with the syndrome which actually involves more often a duodenal tumour of GIST type than a somatostatin secreting neoplasia. Other neuroendocrine tumours are reported: Gastrointestinal NENs at the level of rectum or jejunum and pheocromocytoma. Overall, one quarter of subjects have gastrointestinal tumours of different types. Somatostatinoma, when not located on pancreas but in duodenoum, may be registered in subjects with neurofibromatosis type 1 most probably in addition to other tumours. Overall, this type of neuroendocrine tumour with a challenging presentation has a poor prognosis unless adequate radical surgery is promptly offered to the patient.