The first E59Q mutation identified in the NEUROD1 gene in a Chinese family with maturity-onset diabetes of the young: an observational study

Objective::In contrast to the most commonly reported forms of maturity-onset diabetes of the young(MODY),including MODY2,MODY3 and MODY5,MODY6 is a relatively rare subtype.To investigate whether NEUROD1 is responsible for MODY in Chinese individuals,we screened its mutations in MODY pedigrees and explored the potential pathogenic mechanisms.Methods::Polymerase chain reaction direct sequencing was performed to screen NEUROD1 mutations in 32 Chinese MODY probands who were negative for the GCK/MODY2,HNF1A/MODY3 and HNF1B/MODY5 genes in this observational study.In addition,we enrolled 201 unrelated,non-diabetic control subjects of Han Chinese descent.The functional significance of newly identified mutations was analyzed using clinical phenotype,pathophysiology and three-dimensional structure studies.This study was approved by the Institutional Review Board of Shanghai Jiao Tong University Affiliated Sixth People’s Hospital,China(approval No.YS-2017-83)on March 3,2017.Results::E59Q(c.175 G>C,p.Glu59Gln),a heterozygous missense mutation in the NEUROD1 gene,was identified in one family with MODY.The Glu59 residue in NeuroD1 is highly conserved across mammalian species.Four diabetic patients carrying the mutation(a proband and her son,brother and sister)were lean,with a body mass index of 20.9(20.3-21.2)kg/m 2.Compared with their unaffected relatives(n=4),E59Q carriers(n=4)had significantly decreased ratios of fasting and 2-hour insulin to plasma glucose(both fasting plasma insulin/fasting plasma glucose and 2-hour postprandial plasma insulin/2-hour postprandial plasma glucose,P<0.005).The proband’s father had an E59Q mutation and normal glucose tolerance,which suggested non-penetrance.The E59Q mutation was not detected in other probands or in the 201 control subjects with normal glucose tolerance.Two salt-bridge bonds of Glu59 were disrupted at the Q59 mutation site.Conclusion::The NEUROD1-E59Q mutation changed the molecular conformation of the N-terminal in NeuroD1,which may decrease binding of the E59Q mutant to the insulin promoter and insulin gene transcription activity,therefore causing the MODY6 subtype with defective insulin secretion.

青少年的成人起病型糖尿病家系NEUROD1基因突变的筛查与功能解析

目的·筛查青少年的成人起病型糖尿病(maturity-onset diabetes of the young,MODY)家系中NEUROD1基因突变,分析突变与中国人MODY6发病的相关性及其潜在的致病机制。方法·采用PCR-直接测序法对96例GCK/MODY2、HNF1A/MODY3、HNF1B/MODY5突变阴性的中国MODY先证者进行NEUROD1突变筛查,同时比较96例MODY先证者与100例非糖尿病对照者NEUROD1基因变异的基因型频率。采用从头建模法构建NEUROD1蛋白野生型和突变体的3D结构,采用双荧光素酶报告基因系统检测野生型和突变体蛋白对胰岛素基因转录活性的影响。结果·在一个MODY家系中发现NEUROD1基因杂合错义突变Glu59Gln (NM_002500.5,c.175G>C)。3D结构分析发现,该突变将野生型中带负电荷的Glu59转化为突变中不带电荷的Gln59,导致两个盐桥键Glu59-Arg54和Glu59-Lys88缺失,并形成一个新的氢键Gln59-Arg54。与野生型相比,Glu59Gln突变体的胰岛素基因转录活性下降36.3%(P<0.05)。与非糖尿病对照相比,96例MODY先证者中Ala45Thr (G-A)变异的AA+GA基因型频率显著升高(P=0.002)。结论·Glu59Gln突变改变了NEUROD1蛋白N端的分子构象,导致其胰岛素基因转录活性显著下降,是该家系突变携带者胰岛素分泌缺陷的原因。Ala45Thr变异与MODY6先证者糖尿病发病年龄的提前有关。

早发2型糖尿病家系NeuroD1基因突变筛查与功能研究

目的在中国人早发2型糖尿病家系先证者中筛查NeuroD1基因突变／变异，并研究其功能及携带者家系的临床表型和遗传特点。方法用PCR-直接测序法检测85例早发、95例晚发2型糖尿病家系先证者和87名非糖尿病对照者NeuroD1基因突变／变异，比较筛查到的组间突变／变异的基因型及等位基因频率的差异。分别构建含小鼠NeuroD1（mND1）基因cDNA的野生型、突变型表达质粒载体和与人胰岛素基因启动子相连的荧光素酶报告基因质粒载体，共转染至大鼠INS-1细胞。分别检测荧光素酶活性，比较野生型、突变体蛋白对人胰岛素基因转录活性的影响。结果在一早发先证者发现新突变S159P（T→C），它与来自父方的4例携带突变的糖尿病患者遗传上呈共分离；与野生型相比，S159P突变体导致胰岛素基因转录活性下降25％；检测到常见多态A45T（G→A），与非糖尿病组及晚发2型糖尿病组相比，早发组该变异的AA＋GA基因型频率显著增加（P=0．006和P=0．014）。结论NeuroD1基因S159P突变促进该早发2型糖尿病家系的发病。A45T变异增加中国人早发2型糖尿病的易感性，或与之呈连锁不平衡，该变异可能影响中国人2型糖尿病的发病方式，即早发而不是晚发。

2型糖尿病NEUROD1基因的研究

47例 2型糖尿病 (均 40岁以后发病 )家系先证者PCR SSCP检测出两种NEUROD1基因变异 ;Ala45Thr和Ile15 6Ile。 12 2例 40岁以后发病的 2型糖尿病患者和 13 2例正常对照Ala45Thr基因型和基因频率分布差异无显著性 ,提示NEUROD1基因Ala45Thr突变不是中国人 2型糖尿病的重要遗传因素。