A Family Report Of Charcot-Marie-Tooth Disease Type 4C Was Induced By Novel Mutations In The SH3TC2 Gene And Previous Literature Review Analysis

Background:Charcot-Marie-Tooth disease Type 4C(CMT4C)is an autosomal recessive neuropathy.Its clinical features are early-onset severe scoliosis,foot deformities,distal limb weakness and atrophy,sensory disorders and cranial nerve involvements,which are often associated with SH3TC2 gene mutations on chromosome 5q32.Nearly 100 kinds of SH3TC2 mutations have been found all over the world.Objective:To investigate the genotype phenotype relationship of SH3TC2 gene in a CMT4C family by reporting the clinical manifestations,neuroelectrophysiology,neuroultrasound,gene mutation characteristics and clinical data of CMT4C patients reported at home and abroad,so as to provide help for molecular diagnosis of CMT4C.Methods:This study identified a CMT4C families with compound heterozygous SH3TC2 mutations,who were admitted to the Department of Neurology of the first Hospital of Shanxi Medical University on August 5,2020.They were evaluated with clinical examination and electrophysiologic studies.and the pedigree map was drawn.Genomic DNA was extracted from the peripheral blood and and whole-exome sequencing(WES)was performed in proband.single nucleotide mutation(SNVs)and small insertion /deletion(INDELs)were further predicted by Mutitation taster,Polyphen-2 and SIFT software,and was compared with the single nucleus polymorphism database(db SNP),Exome Aggregation Consortium(Ex AC)and the 1000 Genomes Project.At the same time,200 controls were included to screen the mutant genes.The validation was performed by Sanger sequencing in other members of the family.The structure of mutant protein was constructed by Swiss model,and the wild type and mutant protein were modeled by Swiss PDB viewer 4.1 molecular visualization software.All the patients with CMT4C who had been reported at home and abroad were searched and all the cases that met the statistical criteria were collected,and the relationship between SH3TC2 gene mutation site and clinical feature was analyzed.Results:Proband and the other two patients in this family had an early onset and moderate progression.The main clinical manifestations are progressive weakness and atrophy of distal limbs,varying degrees of sensory impairment,arched feet,scoliosis and cranial involvement,such as hearing loss.The compound heterozygous mutation c.730(exon 6)C>T(p.Q244*)and c.3143(exon13)T>C(p.L1048P)was detected in the SH3TC2 gene of the proband and two siblings.Sanger sequencing confirmed that the compound heterozygous mutation was co segregated with clinical phenotype,and no compound heterozygous mutation was found in 200 normal controls.By searching db SNP,Thousand human genome,Gnom AD,Gnom AD East Asia and other databases,c.730C>T and c.3143T>C compound heterozygous mutations were novel mutations not reported.According to the classification criteria and guidelines of the American Society for medical genetics and genomics(ACMG),c.730C>T mutation is classified as "pathogenic mutation",and c.3143T>C mutation is classified as "undetermined mutation".In the molecular structure modeling,the c.3143T>C mutation led to the substitution of leucine by proline at position 1048,which only formed a hydrogen bond with arginine,resulting in abnormal protein structure and functional changes.In this study,we referenced 55 samples of CMT4C in 24 articles,SH3TC2 mutations were mainly c.3325 C>T(p.R1109*)or c.2860 C>T(p.R954*),with a total of 49 cases,including 11 homozygous mutations and 16 compound heterozygous mutations of c.3325 C>T,7 homozygous mutations and 15 compound heterozygous mutations of c.2860 C>T.And a total of 49 patients with c.3325 C>T and c.2860 C>T mutations were analyzed:(1)c.2860 C>T(28.57%)had a higher incidence of spinal deformity(χ~2 = 9.116,P = 0.003)than c.3325 C>T(00.00%);(2)c.2860 C>T(95.24%)had a higher incidence of foot deformity(χ~2 = 41.174,P < 0.001)than c.3325 C>T(3.57%);(3)Hearing impairment was more frequent with c.2860 C>T(100%)than with c.3325 C>T(33.33%)(χ~2 = 7.875,P = 0.005);(4)c.3325 C>T and c.2860 C>T were significantly different in deep tendon reflexes(χ~2 = 7.424,P = 0.006);(5)c.3325 C>T and c.2860 C>T were significantly correlated with patient nationality(χ~2 = 49.00,P <0.001),where c.3325 C>T occurred only in patients of Spanish nationality;(6)c.3325C>T and c.2860 C>T mutations were not statistically significant in terms of gender,age of onset,severity,CMTNS score,nor in regard to ethnicity and clinical features such as spinal deformity,hearing loss in patients of different gender,c.3325 C>T homozygous mutation and compound heterozygous mutation have no statistical significance in spinal deformity,arch foot and hearing impairment,and c.2860 C>T homozygous mutation and compound heterozygous mutation have no statistical significance in the above three aspects.Conclusion:We report a CMT4C family with a novel c.730(exon6)C > T and c.3143(exon13)T > C compound heterozygous mutation in SH3TC2 gene.The clinical features of the family are early-onset scoliosis,hearing loss,foot drop and peripheral neuropathy.The protein molecular model suggested that the mutated protein had abnormal structure and changed function.The hot spot mutations of SH3TC2 gene(c.3325 C>T and c.2860 C>T)have a founder effect.And c.2860 C>T had a high incidence of foot deformity,spinal deformity and sensorineural hearing loss than c.3325 C>T.