Mutational Spectrum and Genotype-phenotype Correlations in Neurofibromatosis Type 1 Patients from North Macedonia: Identification of Ten Novel NF1 Pathogenic Variants

BACKGROUND: Neurofibromatosis type 1 (NF1) is an autosomal dominant neurocutaneous disorder, characterized by multiple café-au-lait macules, axillary and inguinal freckling, tumors of the nervous system, and iris hamartomas. More than 3,100 different pathogenic variants have been reported in the NF1 gene, including missense, nonsense, frameshift, in-frame, splicing, and large deletions. AIMS: To determine the NF1 mutational spectrum in patients with NF1 from the Republic of North Macedonia. STUDY DESIGN: A cohort study. METHODS: Molecular analyses included reverse transcription and cDNA sequencing of the NF1 gene and next-generation sequencing using the TruSight Cancer panel, along with the multiple ligation probe amplification method to detect single nucleotide variants and copy number variations. Direct DNA sequencing was also used for the family member analysis. RESULTS: Our 9-year study of patients suspected of having NF1 in the Republic of North Macedonia encompassed molecular characterization of 30 cases of the disease. We identified 28 unique pathogenic NF1 variants (NM_001042492.3), of which ten were novel: c.208delA; c.341_364del; c.1480_1481delTT; c.2325+1G>C; c.2495_2496dupAC; c.2533_2541del; c.4517delC; c.5844C>G; c.6971delA; c.7605_7606delGAinsAT. In addition to the variant spectrum analysis, our research revealed two positive genotypephenotype correlations. One between the clinical manifestation of cognitive impairment and gross deletions in the NF1 gene, and the other between cognitive impairment and truncating variants located in the RAS-GAP functional domain. CONCLUSION: This is the first study of NF1 patients in the Republic of North Macedonia, and it contributes ten novel variants to the global spectrum of pathogenic NF1 variants. It also corroborates the crucial importance of NF1 genetic testing for a prompt and precise diagnosis, particularly in younger patients.