Maturity-Onset Diabetes of the Young: An Overview with Focus on the Middle East.

Today, there are more than 32 million patients with diabetes in the Middle East (ME), the number is expected to double by 2040. In contrast to Europe and North America and despite the high prevalence of diabetes in ME, epidemiological data about incident and types of diabetes in the region is very limited. Maturity-onset diabetes of the young (MODY) is a subtype of monogenic diabetes representing 2-5% of all diabetes patients. The disease is autosomal dominant mode of inheritance characterized by ß-cell malfunction below the age of 35 years. To date, there are 15 different MODY forms that have been identified; each has a distinct genetic etiology. It is very common that MODY is misdiagnosed between with type 1 or type 2 diabetes. Hence, accurate genetic diagnosis is crucial to individualize the treatment and to improve glycaemia control. New technologies such as next-generation sequencing (NGS) offer an excellent alternative to screen and identify causative MODY mutations. In this review, we summarize the main clinical and genetic characteristics for each MODY form. In addition, we shed light on MODY studies that have been executed in the ME region.

γ-Aminobutyric acid (GABA) signalling in human pancreatic islets is altered in type 2 diabetes.

AIMS/HYPOTHESIS: γ-Aminobutyric acid (GABA) is a signalling molecule in the interstitial space in pancreatic islets. We examined the expression and function of the GABA signalling system components in human pancreatic islets from normoglycaemic and type 2 diabetic individuals. METHODS: Expression of GABA signalling system components was studied by microarray, quantitative PCR analysis, immunohistochemistry and patch-clamp experiments on cells in intact islets. Hormone release was measured from intact islets. RESULTS: The GABA signalling system was compromised in islets from type 2 diabetic individuals, where the expression of the genes encoding the α1, α2, ß2 and ß3 GABA(A) channel subunits was downregulated. GABA originating within the islets evoked tonic currents in the cells. The currents were enhanced by pentobarbital and inhibited by the GABA(A) receptor antagonist, SR95531. The effects of SR95531 on hormone release revealed that activation of GABA(A) channels (GABA(A) receptors) decreased both insulin and glucagon secretion. The GABA(B) receptor antagonist, CPG55845, increased insulin release in islets (16.7 mmol/l glucose) from normoglycaemic and type 2 diabetic individuals. CONCLUSIONS/INTERPRETATION: Interstitial GABA activates GABA(A) channels and GABA(B) receptors and effectively modulates hormone release in islets from type 2 diabetic and normoglycaemic individuals.

A common variant upstream of the PAX6 gene influences islet function in man.

AIMS/HYPOTHESIS: Impaired glucose tolerance and impaired insulin secretion have been reported in families with PAX6 mutations and it is suggested that they result from defective proinsulin processing due to lack of prohormone convertase 1/3, encoded by PCSK1. We investigated whether a common PAX6 variant would mimic these findings and explored in detail its effect on islet function in man. METHODS: A PAX6 candidate single nucleotide polymorphism (rs685428) was associated with fasting insulin levels in the Diabetes Genetics Initiative genome-wide association study. We explored its potential association with glucose tolerance and insulin processing and secretion in three Scandinavian cohorts (N = 8,897 individuals). In addition, insulin secretion and the expression of PAX6 and transcriptional target genes were studied in human pancreatic islets. RESULTS: rs685428 G allele carriers had lower islet mRNA expression of PAX6 (p = 0.01) and PCSK1 (p = 0.001) than AA homozygotes. The G allele was associated with increased fasting insulin (p (replication) = 0.02, p (all) = 0.0008) and HOMA-insulin resistance (p (replication) = 0.02, p (all) = 0.001) as well as a lower fasting proinsulin/insulin ratio (p (all) = 0.008) and lower fasting glucagon (p = 0.04) and gastric inhibitory peptide (GIP) (p = 0.05) concentrations. Arginine-stimulated (p = 0.02) insulin secretion was reduced in vivo, which was further reflected by a reduction of glucose- and potassium-stimulated insulin secretion (p = 0.002 and p = 0.04, respectively) in human islets in vitro. CONCLUSIONS/INTERPRETATION: A common variant in PAX6 is associated with reduced PAX6 and PCSK1 expression in human islets and reduced insulin response, as well as decreased glucagon and GIP concentrations and decreased insulin sensitivity. These findings emphasise the central role of PAX6 in the regulation of islet function and glucose metabolism in man.

Insulin promoter DNA methylation correlates negatively with insulin gene expression and positively with HbA(1c) levels in human pancreatic islets.

AIMS/HYPOTHESIS: Although recent studies propose that epigenetic factors influence insulin expression, the regulation of the insulin gene in type 2 diabetic islets is still not fully understood. Here, we examined DNA methylation of the insulin gene promoter in pancreatic islets from patients with type 2 diabetes and non-diabetic human donors and related it to insulin expression, HbA(1c) levels, BMI and age. METHODS: DNA methylation was analysed in 25 CpG sites of the insulin promoter and insulin mRNA expression was analysed using quantitative RT-PCR in pancreatic islets from nine donors with type 2 diabetes and 48 non-diabetic donors. RESULTS: Insulin mRNA expression (p = 0.002), insulin content (p = 0.004) and glucose-stimulated insulin secretion (p = 0.04) were reduced in pancreatic islets from patients with type 2 diabetes compared with non-diabetic donors. Moreover, four CpG sites located 234 bp, 180 and 102 bp upstream and 63 bp downstream of the transcription start site (CpG -234, -180, -102 and +63, respectively), showed increased DNA methylation in type 2 diabetic compared with non-diabetic islets (7.8%, p = 0.03; 7.1%, p = 0.02; 4.4%, p = 0.03 and 9.3%, p = 0.03, respectively). While insulin mRNA expression correlated negatively (p < 1 × 10(-6)), the level of HbA(1c) correlated positively (p ≤ 0.01) with the degree of DNA methylation for CpG -234, -180 and +63. Furthermore, DNA methylation for nine additional CpG sites correlated negatively with insulin mRNA expression (p ≤ 0.01). Also, exposure to hyperglycaemia for 72 h increased insulin promoter DNA methylation in clonal rat beta cells (p = 0.005). CONCLUSIONS/INTERPRETATIONS: This study demonstrates that DNA methylation of the insulin promoter is increased in patients with type 2 diabetes and correlates negatively with insulin gene expression in human pancreatic islets.

Enhancement of glucagon secretion in mouse and human pancreatic alpha cells by protein kinase C (PKC) involves intracellular trafficking of PKCalpha and PKCdelta.

AIMS/HYPOTHESIS: Protein kinase C (PKC) regulates exocytosis in various secretory cells. Here we studied intracellular translocation of the PKC isoenzymes PKCalpha and PKCdelta, and investigated how activation of PKC influences glucagon secretion in mouse and human pancreatic alpha cells. METHODS: Glucagon release from intact islets was measured in static incubations, and the amounts released were determined by RIA. Exocytosis was monitored as increases in membrane capacitance using the patch-clamp technique. The expression of genes encoding PKC isoforms was analysed by real-time PCR. Intracellular PKC distribution was assessed by confocal microscopy. RESULTS: The PKC activator phorbol 12-myristate 13-acetate (PMA) stimulated glucagon secretion from mouse and human islets about fivefold (p < 0.01). This stimulation was abolished by the PKC inhibitor bisindolylmaleimide (BIM). Whereas PMA potentiated exocytosis more than threefold (p < 0.001), BIM inhibited alpha cell exocytosis by 60% (p < 0.05). In mouse islets, the PKC isoenzymes, PKCalpha and PKCbeta1, were highly abundant, while in human islets PKCeta, PKCepsilon and PKCzeta were the dominant variants. PMA stimulation of human alpha cells correlated with the translocation of PKCalpha and PKCdelta from the cytosol to the cell periphery. In the mouse alpha cells, PKCdelta was similarly affected by PMA, whereas PKCalpha was already present at the cell membrane in the absence of PMA. This association of PKCalpha in alpha cells was principally dependent on Ca(2+) influx through the L-type Ca(2+) channel. CONCLUSIONS/INTERPRETATION: PKC activation augments glucagon secretion in mouse and human alpha cells. This effect involves translocation of PKCalpha and PKCdelta to the plasma membrane, culminating in increased Ca(2+)-dependent exocytosis. In addition, we demonstrated that PKCalpha translocation and exocytosis exhibit differential Ca(2+) channel dependence.

Identification of Helicobacter pylori and other Helicobacter species by PCR, hybridization, and partial DNA sequencing in human liver samples from patients with primary sclerosing cholangitis or primary biliary cirrhosis.

Helicobacter pylori was identified in human liver tissue by PCR, hybridization, and partial DNA sequencing. Liver biopsies were obtained from patients with primary sclerosing cholangitis (n = 12), primary biliary cirrhosis (n = 12), and noncholestatic liver cirrhosis (n = 13) and (as controls) normal livers (n = 10). PCR analyses were carried out using primers for the Helicobacter genus, Helicobacter pylori (the gene encoding a species-specific 26-kDa protein and the 16S rRNA), Helicobacter bilis, Helicobacter pullorum, and Helicobacter hepaticus. Samples from patients with primary biliary cirrhosis and primary sclerosing cholangitis (11 and 9 samples, respectively) were positive by PCR with Helicobacter genus-specific primers. Of these 20 samples, 8 were positive with the 16S rRNA primer and 9 were positive with the 26-kDa protein primer of H. pylori. These nine latter samples were also positive by Southern blot hybridization for the amplified 26-kDa fragment, and four of those were verified to be H. pylori by partial 16S rDNA sequencing. None of the samples reacted with primers for H. bilis, H. pullorum, or H. hepaticus. None of the normal livers had positive results in the Helicobacter genus PCR assay, and only one patient in the noncholestatic liver cirrhosis group, a young boy who at reexamination showed histological features suggesting primary sclerosing cholangitis, had a positive result in the same assay. Helicobacter positivity was thus significantly more common in patients with cholestatic diseases (20 of 24) than in patients with noncholestatic diseases and normal controls (1 of 23) (P = <0.00001). Patients positive for Helicobacter genus had significantly higher values of alkaline phosphatases and prothrombin complex than Helicobacter-negative patients (P = 0.0001 and P = 0.0003, respectively). Among primary sclerosing cholangitis patients, Helicobacter genus PCR positivity was weakly associated with ulcerative colitis (P = 0.05). Significant differences related to blood group or HLA status were not found.