[Genetic analysis of a fetus pedigree affected with Thyroid dyshormonogenesis type 5 combined with familial Neurofibromatosis type 1].

Objective: To explore the genetic testing outcomes of a fetal family with Thyroid dyshormonogenesis type 5 (TDH5) and familial Neurofibromatosis type 1 (NF1), and to clarify the association between clinical manifestations and genetic variations.

Methods: One case of a TDH5 combined with familiar NF1 fetus treated at Gansu Maternal and Child Health Hospital in January 2024 was selected as the research subject. The clinical and family history data of the fetus were collected by retrospective research method. 10-15 mL of fetal amniotic fluid, and 2-3 mL of peripheral blood from the parents, sister, and grandfather of the fetus were collected, and genomic DNA was extracted for trio whole-exome sequencing (trio-WES). The Sanger sequencing was utilized to validate candidate variants for family verification. According to the Standards and Guidelines for the Interpretation and Reporting of Sequence Variants of the American Society of Medical Genetics and Genomics (ACMG) (hereafter referred to as the ACMG guidelines), the pathogenicity of the detected variants was classified. This study has been approved by the Medical Ethics Committee of Gansu Maternal and Child Health Hospital [Ethics No.（2021）GSFY（65）].

Results: The fetal ultrasound indicated the nuchal translucency (NT) thickening, and the thyroid function test results of the sister showed an increase in thyroid stimulating hormone and a decrease in free thyroid hormone. Simultaneously, there were cafe-au-lait macules of various sizes in multiple parts of the body of the sister, and the mother had a similar cafe-au-lait macules phenotype. The trio-WES results revealed that there was a c.413dupA (p.Tyr138*) frameshift mutation in exon4 and c.573G>A (p.Trp191*) nonsense mutation in exon5 of the fetal DUOXA2, which were inherited from the mother and father, respectively. In accordance with the ACMG guidelines, they were classified as pathogenic variant (PVS1+PM2_Supporting+PM3) and likely pathogenic variant (PVS1+PM2_Supporting), respectively. And the nonsense mutation c.6972C>A (p.Tyr2264*) was detected in exon46 of the NF1 in the fetus, inherited from the mother maternal grandfather. The genetic testing results of the first sister and proband in this case were consistent, and the DUOXA2 and NF1 of the second sister were both wild-type. According to the ACMG guidelines, c.6972C>A (p.Tyr2264 *) was classified as pathogenic variant (PVS1+PS4_Supporting+PP4+PM2_Supporting).

Conclusion: The mutations in the DUOXA2 gene c.413dupA (p.Tyr138*) and c.573G>A (p.Trp191*), and the NF1 gene c.6972C>A (p.Tyr2264*) might be the genetic causes of TDH5 combined with familiar NF1 in proband. The discovery of the DUOXA2 gene c.573G>A (p.Trp191*) enriches the spectrum of pathogenic gene variations.