Two Cases And Functional Study Of MODY2 Induced By A Novel Site Mutation Of Glucokinase Gene

Research background:maturity-onset diabetes of the young(MODY)is an autosomal dominant inherited disease caused by single gene mutations.Fourteen types of MODY2 have been identified,among which MODY2 caused by a heterozygous inactivation mutation of GCK gene.Patients with MODY2 are often misdiagnosed as type 1 or type 2 diabetes due to their insidious onset and variable clinical symptoms.In recent years,due to the development of molecular diagnosis technology,an increasing number of MODY2 patients have been correctly diagnosed and treated through genetic testing technology.So far,the clinical features of MODY2 caused by the newly identified heterozygous mutation of the GCK gene(c.297G>A,p.W99X)and the molecular mechanism of the mutation have not been reported.In this paper,the clinical characteristics and function of this mutation of GCK gene were analyzed.In addition,the clinical characteristics of all patients with nonsense mutations of GCK gene previously reported in the literature were summarized in order to provide experience for the clinical diagnosis and treatment of this disease.Research methods:1.The basic information and laboratory test results of the proband and his parents were collected,and the genetic testing was performed on the proband and his parents by the method of diabetes Panel gene tests.2.The 3D structure model of the mutant protein was predicted according to the mutation site.3.The plasmid was constructed(labeled with 3xFlag and GFP labels)and expressed in human embryonic kidney cells(HEK-293A cells)and the protein was extracted to obtain wild-type and mutant recombinant proteins.4.Western blotting was Performed to determine the molecular weight of the wild type and mutant proteins.5.Clinical follow-up was conducted for three times and collect relevant laboratory test results.6.Continuous glucose monitoring was performed in the patient and his mother carrying the same mutation using Abbott instantaneous glycemometer to observe the changes of daily blood glucose level under different dietary states.7.All literatures on nonsense mutations of GCK gene were searched through the human gene mutation database and the clinical data of these patients were summarized.Results:The Panel gene test was performed on the proband and his parents were verified.Heterozygous variation of GCK gene(c.297G>A,p.W99X)was found in the genes of both the proband and his mother.This mutation in the GCK gene leads to the production of truncated glucokinase,which lacks the site to bind glucose,affects glucose metabolism,resulting in the occurrence of MODY2.Although carrying the same genetic mutation,the two cases had different OGTT results.The diet was effective for their glycemic control and was able not only to reduce glycemic excursions but also to increase TIR.Dynamic blood glucose monitoring can reveal that even on a controlled diet,there is still an increase in postprandial blood glucose levels.In addition,the genotype of nonsense mutations in GCK gene appear to be indepandent of their clinical presentation.Conclusions:1.A novel GCK gene mutation site was identified for the first time.This mutation produces a truncated glucokinase,which lacks the glucose binding site and is unable to perform normal function,resulting in the disturbance of glucose metabolism in two family members carrying the mutation.2.Controlling diet can reduce the fluctuations of blood glucose and increase TIR.3.For patients with MODY2,attention should still be paied to postprandial blood glucose.4.The clinical phenotype of patients with nonsense mutation of GCK gene may be independent of genotype.