Individuals with higher-than-normal blood sugar levels used to be diagnosed as having either type 1 or type 2 diabetes. We now know that a wide range of different factors can cause diabetes, including single gene defects, which account for at least 1% of all diabetes cases and up to 4% of cases in the pediatric population. However, misdiagnosis remains common due to the considerable clinical overlap between the different diabetes forms. Monogenic diabetes onset can occur shortly after birth, as observed in neonatal diabetes mellitus, or any time later in life. The present chapter outlines the genes currently known to be involved in monogenic diabetes. Some of these genes are involved in β-cell development, with mutations often leading to a decreased β-cell number, while others play important roles in β-cell function and maintenance. Monogenic forms of autoimmune diabetes and epigenetic causes will also be discussed. A genetic diagnosis may influence treatment choice and prognosis determination and may also lead to family counseling. Genetic screening using next-generation sequencing is becoming more practical as it becomes increasingly accessible and less expensive.

Objective When diabetes is associated with congenital malformations, without autoimmune antibodies, a genetic cause is suspected. Here, we aimed to identify a defective gene that led to diabetes. Research Design and Methods We performed an exome analysis of an index case and his healthy parents. Results The child presented with childhood‐onset diabetes, congenital hypopituitarism, cardiac malformation, and anal atresia. A DNA analysis revealed a heterozygous de novo pathogenic variant in the developmental transcription factor, forkhead box A2 (FOXA2). The mutation resided in the DNA‐binding domain, which is highly conserved among species. Tridimensional molecular dynamics simulation modeling predicted an altered interaction between the mutated protein and DNA. Conclusions A defect in the FOXA2 DNA‐binding domain was associated with childhood‐onset diabetes and multiple congenital anomalies, which reflected the pleiotropic nature of the gene. This report extends the recently described phenotype of neonatal hypoglycemia to later‐onset diabetes. We suggest to include FOXA2 analysis for neonatal hypoglycemia and to implement a long‐term follow‐up, particularly for the risk of diabetes.

Background: Gain-of-function mutations in the GLUD1 gene, encoding for glutamate dehydrogenase (GDH), result in the hyperinsulinism/hyperammonemia HI/HA syndrome. HI/HA patients present with harmful hypoglycemia secondary to protein-induced HI and elevated plasma ammonia levels. These symptoms may be accompanied by seizures and mental retardation. GDH is a mitochondrial enzyme that catalyzes the oxidative deamination of glutamate to α-ketoglutarate, under allosteric regulations mediated by its inhibitor GTP and its activator ADP. The present study investigated the functional properties of the GDH-G446V variant (alias c.1496G > T, p.(Gly499Val) (NM_005271.4)) in patient-derived lymphoblastoid cells. Results: The calculated energy barrier between the opened and closed state of the enzyme was 41% lower in GDH-G446V compared to wild-type GDH, pointing to altered allosteric regulation. Computational analysis indicated conformational changes of GDH-G446V in the antenna region that is crucial for allosteric regulators. Enzymatic activity measured in patient-derived lymphoblastoid cells showed impaired allosteric responses of GDH-G446V to both regulators GTP and ADP. In particular, as opposed to control lymphoblastoid cells, GDH-G446V cells were not responsive to GTP in the lower range of ADP concentrations. Assessment of the metabolic rate revealed higher mitochondrial respiration in response to GDH-dependent substrates in the GDH-G446V lymphoblastoid cells compared to control cells. This indicates a shift toward glutaminolysis for energy provision in cells carrying the GDH-G446V variant. Conclusions: Substitution of the small amino acid glycine for the hydrophobic branched-chain valine altered the allosteric sensitivity to both inhibitory action of GTP and activation by ADP, rendering cells metabolically responsive to glutamine.