Common variants of HNF1A gene are associated with diabetic retinopathy and poor glycemic control in normal-weight Japanese subjects with type 2 diabetes mellitus

A Review of Functional Characterization of Single Amino Acid Change Mutations in HNF Transcription Factors in MODY Pathogenesis

Mutations in HNF transcription factor genes cause the most common subtypes of maturity-onset of diabetes of youth (MODY), a monogenic form of diabetes mellitus. Mutations in the HNF1-α, HNF4-α, and HNF1-β genes are primarily considered as the cause of MODY3, MODY1, and MODY5 subtypes, respectively. Although patients with different subtypes display similar symptoms, they may develop distinct diabetes-related complications and require different treatments depending on the type of the mutation. Genetic analysis of MODY patients revealed more than 400 missense/nonsense mutations in HNF1-α, HNF4-α, and HNF1-β genes, however only a small portion of them are functionally characterized. Evaluation of nonsense mutations are more direct as they lead to premature stop codons and mostly in mRNA decay or nonfunctional truncated proteins. However, interpretation of the single amino acid change (missense) mutation is not such definite, as effect of the variant may vary depending on the location and also the substituted amino acid. Mutations with benign effect on the protein function may not be the pathologic variant and further genetic testing may be required. Here, we discuss the functional characterization analysis of single amino acid change mutations identified in HNF1-α, HNF4-α, and HNF1-β genes and evaluate their roles in MODY pathogenesis. This review will contribute to comprehend HNF nuclear family-related molecular mechanisms and to develop more accurate diagnosis and treatment based on correct evaluation of pathologic effects of the variants.

Association of Common Variants in HNF1A Gene with Serum AFP Level in Healthy Chinese Individuals and HCC Patients

Although alpha-fetoprotein (AFP) is a widely used tumor marker in hepatocellular carcinoma (HCC), 40% of newly diagnosed patients do not have an elevated AFP level. Research has revealed that mutations in the HNF1A binding site of the AFP gene promoter cause significantly elevated serum AFP levels in patients with hereditary persistence of AFP. This study investigated the relationship between HNF1A genetic variants and serum AFP levels. We examined the association between the HNF1A-rs1169288 (A/C), rs2464196 (G/A), and rs1169310 (C/T) polymorphisms and AFP levels in a healthy Chinese population (n = 1010) and HCC patients (n = 185). Single nucleotide polymorphisms were genotyped by the amplification refractory mutation system combined with TaqMan probe in real-time PCR. The serum AFP concentrations were measured using the Architect i2000 immunochemistry analyzer. In healthy individuals, serum AFP levels were significantly lower with the rs2464196-AA and rs1169310-TT genotypes. Similar significant differences were observed in HCC patients. Moreover, in HCC patients, the distribution frequencies of rs2464196-AA+AG and rs1169310-TT+TC among those with AFP ≤ 20 ng/ml or ≤400 ng/ml were significantly lower than those in patients with AFP > 20 ng/ml or >400 ng/ml. Among all subjects, those carrying the HNF1A-rs2464196-A or rs1169310-T allele tended to have low levels of AFP. However, the HNF1A-rs1169288 polymorphism showed no significant association with the serum AFP level. These findings provide new insight into the genetic determinants of serum AFP level and can aid the differential diagnosis of HCC patients with low serum AFP.

Genetic Study of Hepatocyte Nuclear Factor 1 Alpha Variants in Development of Early-Onset Diabetes Type 2 and Maturity-Onset Diabetes of the Young 3 in Iran

Background:

Maturity-onset diabetes of the young (MODY) is a clinically and genetically heterogeneous group of diabetes characterized by noninsulin-dependent, autosomal-dominant disorder with strong familial history, early age of onset, and pancreatic beta-cell dysfunction. Mutations in at least 14 different genes are responsible for various MODY subtypes. Heterozygous mutations in the hepatocyte nuclear factor 1 alpha (HNF1A) gene are responsible for the MODY3 subtype, which is a common subtype of MODY in different studied populations. To date, more than 450 different variants of this gene have been reported as disease causing for MODY3. This study was carried out to evaluate HNF1A mutations in Iranian diabetic families fulfilling MODY criteria.

Materials and Methods:

Polymerase chain reaction and Sanger sequencing were performed. All the ten exons of the HNF1A gene were sequenced in ten families, followed by cosegregation analysis and in silico evaluation. Computational protein modeling was accomplished for the identified mutation.

Results:

MODY3 was confirmed in two large families by detecting a mutation (p.G253E) in coding regions of HNF1A. Compound heterozygous state for two common variants in HNF1A (p.I27 L and p.S487N) was detected in affected members of 5 families, and in one family, a rare benign variant in the coding sequence for Kozak sequence was detected. Two new nonpathogenic variants were found in noncoding regions of HNF1A.

Conclusion:

It seems that HNF1A mutations are a common cause of MODY in Iranian diabetic patients. Identified common variants in heterozygous state can cause diabetes Type II in earlier ages. The role of rare variant rs3455720 is unknown, and more investigation is needed to uncover the function of this variant.