Paper
Genotype–Phenotype Correlation in Neurofibromatosis Type 1: Evidence for a Mild Phenotype Associated with Splicing Variants Leading to In-Frame Skipping of NF1 Exon 24 [19a]
Published Jun 29, 2024 · Yunjia Chen, Yulong Fu, Magdalena Koczkowska
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Abstract
Simple Summary Although a large number of NF1 variants have been cataloged in public databases, known NF1 genotype-phenotype correlations are still limited. Through a retrospective analysis of a large cohort of NF1 patients at the Medical Genomics Laboratory of the University of Alabama at Birmingham, we established a novel NF1 genotype-phenotype correlation. Specifically, NF1 patients with NF1 exon 24 [19a] skipping typically exhibit a mild phenotype, characterized by the absence of severe NF1-specific clinical features, including neurofibromas. This newly established genotype-phenotype correlation will help clinicians improve the management of patients harboring NF1 exon 24 [19a] skipping variants and provide a new therapeutic target for NF1 treatment. Abstract Neurofibromatosis type 1 (NF1) is an autosomal dominant neurocutaneous disorder caused by loss-of-function variants in the NF1 gene. As of 20 November 2023, over 5000 distinct pathogenic or likely pathogenic variants have been reported in public databases. However, only a few NF1 genotype–phenotype correlations have been established so far. In this study, we present findings on 40 individuals with NF1, comprising 26 unrelated probands and 14 affected relatives, who carry one of nine NF1 heterozygous pathogenic splicing variants, all of which result in the in-frame skipping of exon 24 [19a] (NM_000267.3:r.3114_3197del, p.Asn1039_Arg1066del). These variants include c.3114-2A>G, c.3114-1G>A, c.3196A>G, c.3197G>A, c.3197G>T, c.3197+1G>A, c.3197+1G>T, c.3197+2T>C, and c.3197+3A>T. Among individuals with these variants, none exhibit externally visible plexiform neurofibromas, histopathologically confirmed cutaneous or subcutaneous neurofibromas, symptomatic spinal neurofibromas, or symptomatic optic pathway gliomas. The most prevalent, and sometimes sole, clinical feature observed in this cohort is multiple café-au-lait macules, with or without skinfold freckles: 85% and 60.5% of the individuals display six or more café-au-lait macules and freckles, respectively. In comparison to established NF1 genotype–phenotype correlations, these patients demonstrate highly similar clinical presentations to those associated with the NF1 pathogenic variant c.2970_2972del (p.Met992del), known for resulting in the mildest clinical features. Despite the generally mild phenotype, cognitive impairment, developmental delay, and/or learning difficulties are still observed in 33.3% of these patients, suggesting that learning challenges remain a prominent aspect of the phenotypic presentation in these individuals and necessitate specialized care. This newly established genotype–phenotype correlation will assist clinicians in improving the management of patients harboring NF1 exon 24 [19a] skipping variants and provide a new therapeutic target for NF1 treatment.
NF1 patients with NF1 exon 24 [19a] skipping variants typically exhibit a mild phenotype, characterized by absence of severe NF1-specific clinical features, including neurofibromas.
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