Aberrant Splicing in GJB1 and the Relevance of 5' UTR in CMTX1 Pathogenesis.

Federica Boso,Ilaria Cabrini,Federica Taioli,Gian Maria Fabrizi,Tiziana Cavallaro

doi:10.3390/brainsci11010024

Abstract

The second most common form of Charcot-Marie-Tooth disease (CMT) follows an X-linked dominant inheritance pattern (CMTX1), referring to mutations in the gap junction protein beta 1 gene (GJB1) that affect connexin 32 protein (Cx32) and its ability to form gap junctions in the myelin sheath of peripheral nerves. Despite the advances of next-generation sequencing (NGS), attention has only recently also focused on noncoding regions. We describe two unrelated families with a c.-17+1G>T transversion in the 5′ untranslated region (UTR) of GJB1 that cosegregates with typical features of CMTX1. As suggested by in silico analysis, the mutation affects the regulatory sequence that controls the proper splicing of the intron in the corresponding mRNA. The retention of the intron is also associated with reduced levels of the transcript and the loss of immunofluorescent staining for Cx32 in the nerve biopsy, thus supporting the hypothesis of mRNA instability as a pathogenic mechanism in these families. Therefore, our report corroborates the role of 5′ UTR of GJB1 in the pathogenesis of CMTX1 and emphasizes the need to include this region in routine GJB1 screening, as well as in NGS panels.

Highlights

Received: 30 November 2020Accepted: 23 December 2020Published: 27 December 2020Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.license.Charcot-Marie-Tooth disease (CMT) refers to the most frequent group of hereditary neuropathies, encompassing a wide range of genetic, clinical, neurophysiological and pathological features
Two young who were for a length-dependent, Two young probands whoprobands were evaluated forevaluated a length-dependent, sensory-motorsensory-motor neuropathy led to the study of two unrelated families on the assumption neuropathy led to the study of two unrelated families on the assumption of a genetic path- of a genetic pathogenesis
Of second patientsmost whocommon are diagnosed with is the mutated gene in patients. This form of typically presents with a length-dependent sensory-motor neuropathy with CMT, accounting for up to 10% of patients who are diagnosed with CMTX1 [2,11]

Summary

Introduction

Received: 30 November 2020Accepted: 23 December 2020Published: 27 December 2020Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.license (https://creativecommons.org/licenses/by/4.0/).Charcot-Marie-Tooth disease (CMT) refers to the most frequent group of hereditary neuropathies, encompassing a wide range of genetic, clinical, neurophysiological and pathological features. The advent of next-generation sequencing (NGS) techniques paved the way for a broader screening of the patients and for the discovery of rarer variants, providing a higher likelihood of identification. Notwithstanding this considerable progress, assuming a Mendelian inheritance, a genetic diagnosis remains elusive in 30–70% of CMT patients [1,2,3,4], depending on customized gene panels that generally cover only known disease-related coding sequences in order to provide a faster and affordable analysis with higher coverage, as well as fewer incidental findings. The most frequent culprit for CMT after peripheral myelin protein

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