Clinical And Basic Study On A De Novo Gene Variant Site In A Patient With MCTT Syndrome

Objective:The core pedigree of a proband with MN1 C-terminal truncation(MCTT)syndrome was collected and sequenced.The clinical characteristics and gene variants of the proband were analyzed and clinical treatment was carried out.The functional analysis of the de novo MN1 variant in the proband will further verify the impact of the MN1 gene variant at the molecular biological level,laying a foundation for the study of the pathogenesis of MCTT syndrome.Methods: A patient with MCTT syndrome and her parents were selected as the object of this study.Peripheral venous blood was extracted for whole-exon sequencing and Sanger sequencing.32 unrelated healthy Chinese were selected as the control group.Peripheral venous blood was extracted for Sanger sequencing.The clinical data of the probands were collected and treated with an individualized reverse sector fan-shaped expander and continuous positive airway pressure.The protein structure of variant MN1 protein was predicted by Alphafold.The variant and wild-type MN1 plasmids were constructed and transfected into HEK293 T cells.The expression levels of MN1,PBX1 and ZBTB24 were analyzed by RT-PCR and Western Blot.Results: The proband has typical clinical symptoms of MCTT syndrome and carries de novo MN1 variants(3760C>T,Q1254 *).After two years of combined treatment of orthodontic and respiratory,the clinical symptoms of the proband were significantly improved.The prediction of protein structure showed that the de novo variant of MN1 caused the C-terminal truncation of MN1 protein.After HEK293 T cells were transfected with MN1 variant and wild-type plasmids,the results of RT-PCR showed that the m RNA expression of MN1 and PBX1 were up-regulated,and the up-regulation of expression was more significant after transfection of MN1 variant.After transfection of MN1 variant plasmid,the m RNA expression of ZBTB24 was up-regulated,while the expression of transfected wild-type plasmid was not significantly up-regulated.The results of Western Blot showed that the expression of MN1,PBX1 and ZBTB24 proteins were up-regulated after transfection of MN1 variant plasmid.After transfection of MN1 wild-type plasmid,the expression of MN1 and PBX1 protein was up-regulated,while the expression of ZBTB24 was not significantly up-regulated.Conclusion: The proband has a typical clinical phenotype of MCTT syndrome and carries a de novo variant of MN1(3760C>T,Q1254 *).The combined treatment of orthodontics and respiratory department is helpful to improve the symptoms of patients with MCTT syndrome.The prediction of protein structure showed that the de novo variant MN1 protein produced a termination codon in advance,resulting in a C-terminal truncation variant of MN1 protein,which may affect the function of MN1 protein.This de novo variant of MN1 may affect the expression of PBX1 and ZBTB24.