Objectives: In contrast to the common MODY2, MODY3 and MODY5, MODY6 is a relatively rare subtype of MODY. To investigate whether NEUROD1 is responsible for Chinese MODY, we screened its mutations in MODY pedigrees and explored the potential pathogenic mechanisms.
Methods: PCR direct sequencing was performed to screen NEUROD1 mutations in 32 Chinese MODY probands who were negative for MODY2, MODY3 and MODY5 genes. The functional significances of newly identified mutations were analyzed by studies on clinical phenotypes, pathophysiology and three-dimensional (3D) structure.
Results: 1) E59Q (c.175 G>C, p.Glu59Gln), a heterozygous mutation in NEUROD1 gene, was identified in one of the MODY families. 2) Glu59 residue in NeuroD1 is highly conserved across mammalian species. 3) Four diabetic patients (proband and her son, brother and sister) carring the mutation were thinner with BMI of 21.0 (20.3-21.2). In comparison with unaffected relatives (n = 6), E59Q carriers showed obviously decreased insulin secretion at fasting and postprandial status (both p<0.05). The proband’s father with E59Q mutation was normal glucose tolerance, suggesting non-penetrants. 4) The E59Q mutation was not detected in other probands or in the 201 nondiabetic control subjects. 5) The negatively charged Glu59 forms hydrogen bonds and strong salt bridges with the surrounding positively charged Arg54 and Lys88, and the main chains of Glu59 forms hydrogen bonds with Gly56 and Asp61, respectively. In the E59Q mutation, the salt bridges of Gln59 side chain disrupts, forming the new hydrogen bonds between Gln59 and Arg54.
Conclusions: NEUROD1-E59Q mutation clearly affected the interaction between E59 residue and its surrounding amino acids and thus changed the molecular conformation of N-terminal in NeuroD1. The abnormal conformation of NeuroD1 may decrease the E59Q mutant binding to the insulin promoter and activity of insulin transcription, therefore causing MODY6 subtype with defected insulin secretion.
L. Liu: None. Y. Chen: None. J. Zhang: None. Y. Jiang: None. M. Lu: None. X. Ge: None. W. Jia: None.
National Natural Science Foundation of China (81970686, 81770791, 81471012, 81270876); Shanghai Jiao Tong University (YG2019ZDA08); Shanghai Leading Talent (SLJ15055)