Mutations In PDX1 Research Articles

What Do We Know about Neonatal Diabetes caused by PDX1 Mutations?

Neonatal diabetes mellitus (NDM) is characterized by severe hyperglycemia, usually diagnosed in the first few months of an individual's life. It is a genetic disease and one of the main forms of monogenic diabetes. Changes in different genes have already been associated with NDM, including changes in the gene PDX1. In this review, we intend to summarize all neonatal diabetes cases caused by PDX1 mutations reported in the literature. For this purpose, we searched keywords in the literature from PubMed and articles cited by the HGMD database. The search retrieved 84 articles, of which 41 had their full text accessed. After applying the study exclusion criteria, nine articles were included. Of those articles, we detected thirteen cases of NDM associated with changes in PDX1; the majority in homozygous or compound heterozygous patients. Until now, variants in the PDX1 gene have been a rare cause of NDM; however, few studies have included the screening of this gene in the investigation of neonatal diabetes. In this review, we reinforce the importance of the PDX1 gene inclusion in genetic NGS panels for molecular diagnosis of NDM, and systematic morphological and functional exams of the pancreas when NDM is present.

Generation of allogenic chimera carrying mutations in PDX1 and TP53 genes via phytohemagglutinin-mediated blastomere aggregation in pigs.

The generation of genetically engineered pig models that develop pancreas-specific tumors has the potential to advance studies and our understanding of pancreatic cancer in humans. TP53 mutation causes organ-nonspecific cancers, and PDX1-knockout results in the loss of pancreas development. The aim of the present study was to generate a PDX1-knockout pig chimera carrying pancreas complemented by TP53 mutant cells via phytohemagglutinin (PHA)-mediated blastomere aggregation using PDX1 and TP53 mutant blastomeres, as a pig model for developing tumors in the pancreas with high frequency. First, the concentration and exposure time to PHA to achieve efficient blastomere aggregation were optimized. The results showed that using 300µg/mL PHA for 10min yielded the highest rates of chimeric blastocyst formation. Genotyping analysis of chimeric blastocysts derived from aggregated embryos using PDX1- and TP53-edited blastomere indicated that approximately 28.6% carried mutations in both target regions, while 14.3-21.4% carried mutations in one target. After the transfer of the chimeric blastocysts into one recipient, the recipient became pregnant with three fetuses. Deep sequencing analysis of the PDX1 and TP53 regions using ear and pancreas samples showed that one fetus carried mutations in both target genes, suggesting that the fetus was a chimera derived from embryo-aggregated PDX1 and TP53 mutant blastomeres. Two out of three fetuses carried only the PDX1 mutation, indicating that the fetuses developed from embryos not carrying TP53-edited blastomeres. The results of the present study could facilitate the further improvement and design of high-frequency developing pancreatic tumor models in pigs.

Clinical and molecular description of two cases of neonatal diabetes secondary to mutations in PDX1.

Pancreatic dysgenesis (PD) is a rare congenital disease, with less than 100 cases reported in the literature. In most cases, patients are asymptomatic and the diagnosis is made incidentally. In this report, we present the case of two brothers with a history of intrauterine growth retardation, low birth weight, hyperglycemia, and poor weight gain. The diagnosis of PD and neonatal diabetes mellitus was made by an interdisciplinary team composed of an endocrinologist, a gastroenterologist, and a geneticist. Once the diagnosis was made, treatment with an insulin pump, pancreatic enzyme replacement therapy, and supplementation with fat-soluble vitamins was decided. The use of the insulin infusion pump facilitated the outpatient treatment of both patients. Pancreatic dysgenesis is a relatively rare congenital anomaly; most of the time, patients are asymptomatic and are diagnosed incidentally. The diagnosis of pancreatic dysgenesis and neonatal diabetes mellitus should be made with an interdisciplinary team. Due to its flexibility, the use of an insulin infusion pump facilitated the management of these two patients.

221-OR: Retrospective Review of Genetic Mutations and Treatments in Patients with Monogenic Diabetes of the Youth (MODY)

Monogenic diabetes results from specific genetic mutations that result in diabetes mellitus. Clinical phenotypes differ based on the genetic defect, and treatment options are driven by the underlying genetic cause. Thus, accurate genetic diagnosis and evaluation of response to treatment is essential. Retrospective chart review was utilized to identify patients with MODY at a single institution who had confirmed genetic mutations. Demographics, co-morbidities, initial islet cell autoantibodies, diagnosis and treatment, and current treatments were evaluated. Patients diagnosed with MODY (n=92) comprised of 3% of the total patient population diagnosed with diabetes (78% T1DM, 19% T2DM) between 2000 to present day. For patients with MODY, the average age of diabetes diagnosis was 10.3 years and their mean HgbA1c was 8.0% at diagnosis. Three and a half percent of patients with MODY had ketoacidosis at diagnosis and 6.7% had positive islet cell autoantibodies. Among patients with MODY, the most common gene mutations were HNF1A, GCK, and HNF1B. Novel genetic mutations in PDX1, RFX6, BLK and KFL11 were also identified. Current treatment modalities of patients with MODY were compared (insulin, Metformin, Sulfonylureas, Metformin-Glyburide, insulin-Metformin, GLP-1 receptor agonists). For each medication, reduction in HgbA1c was seen at follow-up (0.05-1.15% reduction). All medications except for insulin and Metformin-Glyburide demonstrated a reduction in BMI at follow-up. The greatest reduction in BMI was observed in patients on GLP-1 receptor agonists and insulin-Metformin (3.3% and 8.89% respectively). Our study highlights the importance of genetic testing in patients who present with diabetes without ketoacidosis and that testing positive for islet antibodies does not preclude patients from a MODY diagnosis. Moreover, future investigation of GLP-1 receptor agonist as a treatment for MODY patients is warranted. Disclosure L.Deng: None. A.S.Shah: None. M.Krishnamurthy: None.

Prevalence and Clinical Characteristics of PDX1 Variant Induced Diabetes in Chinese Early-Onset Type 2 Diabetes.

Maturity-onset diabetes of the young 4 (MODY4) is caused by mutations of PDX1; its prevalence and clinical features are not well known. This study aimed to investigate the prevalence and clinical characteristics of MODY4 in Chinese people clinically diagnosed with early-onset type 2 diabetes (EOD), and to evaluate the relationship between the PDX1 genotype and the clinical phenotype. The study cohort consisted of 679 patients with EOD. PDX1 mutations were screened by DNA sequencing, and their pathogenicity was evaluated by functional experiments and American College of Medical Genetics and Genomics guidelines. MODY4 was diagnosed in individuals with diabetes who carry a pathogenic or likely pathogenic PDX1 variant. All reported cases were reviewed for analyzing the genotype-phenotype relationship. 4 patients with MODY4 were identified, representing 0.59% of this Chinese EOD cohort. All the patients were diagnosed before 35 years old, either obese or not obese. Combined with previously reported cases, the analysis revealed that the carriers of homeodomain variants were diagnosed earlier than those with transactivation domain variants (26.10 ± 11.00 vs 41.85 ± 14.66 years old, P < .001), and the proportions of overweight and obese individuals with missense mutation were higher than those with nonsense or frameshift mutations (27/34 [79.4%] vs 3/8 [37.5%], P = .031). Our study suggested that MODY4 was prevalent in 0.59% of patients with EOD in a Chinese population. It was more difficult to identify clinically than other MODY subtypes owning to its clinical similarity to EOD. Also, this study revealed that there is some relationship between genotype and phenotype.

Using Human Induced Pluripotent Stem Cell–Derived Organoids to Identify New Pathologies in Patients With PDX1 Mutations

Two patients with homozygous mutations in PDX1 presented with pancreatic agenesis, chronic diarrhea, and poor weight gain, the causes of which were not identified through routine clinical testing. We aimed to perform a deep analysis of the stomach and intestine using organoids derived from induced pluripotent stem cells from PDX1188delC/188delC patients. Gastric fundic, antral, and duodenal organoids were generated using induced pluripotent stem cell lines from a PDX1188delC/188delC patient and an isogenic induced pluripotent stem cell line where the PDX1 point mutation was corrected. Patient-derived PDX1188delC/188delC antral organoids exhibited an intestinal phenotype, whereas intestinal organoids underwent gastric metaplasia with significant reduction in enteroendocrine cells. This prompted a re-examination of gastric and intestinal biopsy specimens from both PDX1188delC/188delC patients, which recapitulated the organoid phenotypes. Moreover, antral biopsy specimens also showed increased parietal cells and lacked G cells, suggesting loss of antral identity. All organoid pathologies were reversed upon CRISPR-mediated correction of the mutation. These patients will now be monitored for the progression of metaplasia and gastrointestinal complications that might be related to the reduced gastric and intestinal endocrine cells. This study demonstrates the utility of organoids in diagnosing uncovered pathologies.

Identification of Maturity-Onset-Diabetes of the Young (MODY) mutations in a country where diabetes is endemic

Genetic variants responsible for Maturity-Onset-Diabetes of the Young (MODY) in Kuwait were investigated. A newly established a National Referral Clinic, the Dasman Diabetes Institute (DDI-NRC), assessed forty-five members from 31 suspected MODY families by whole exome sequencing. Thirty-three of the 45 samples were independently sequenced at the DDI-NRI, Exeter University, UK (https://www.diabetesgenes.org/) using targeted 21-gene panel approach. Pathogenic mutations in GCK, HNF1A, HNF1B, HNF4A, and PDX1 confirmed MODY in 7 families, giving an overall positivity rate of 22.6% in this cohort. Novel variants were identified in three families in PDX1, HNF1B, and HNF1B. In this cohort, Multiplex Ligation-dependent Probe Amplification assay did not add any value to MODY variant detection rate in sequencing negative cases. In highly selected familial autoantibody negative diabetes, known MODY genes represent a minority and 77.3% of the familial cases have yet to have a causal variant described.

256-OR: Using Human Induced Pluripotent Stem Cell Derived Organoids to Identify New Pathologies in Patients with Pdx1 Mutations

Pancreas and gastrointestinal (GI) tract development is guided by several transcription factors, including pancreatic and duodenal homeobox gene-1 (PDX1). While it is well known that PDX1is essential for pancreatic development and beta cell function, its role in GI development and function is not fully understood. We identified a patient with a homozygous point mutation in PDX1 causing total loss of PDX1 protein resulting in pancreatic agenesis. We differentiated induced pluripotent stem cells from the patient into human antral gastric (HAGO) and intestinal (HIO) organoids as a novel diagnostic approach to identify new GI pathologies. Immunofluorescence staining revealed that portions of the PDX1-null HAGOs lost the gastric marker claudin18 and increased intestinal villin1 expression, signifying that regions of the antrum are converting to an intestinal phenotype. Similarly, PDX1-null HIOs lost the intestinal marker cadherin17 and increased claudin18, indicating that regions of the intestine are undergoing gastric metaplasia. Examination of functional markers revealed an increase in acid producing parietal cells, complete lack of gastrin producing endocrine cells in HAGOs, and an increase in gastric surface mucin in HIOs. These in vitro results were further validated using endoscopy biopsies from two patients with PDX1 mutations, which showed a similar disruption in gastric and intestinal identity. CRISPR/Cas9-mediated correction of the PDX1 mutation reversed the observed PDX1-null metaplasic phenotypes in HAGOs and HIOs and also allowed for the successful generation of pancreatic tissue indicating unambiguously that the PDX1 mutation is responsible for these pathologies. Based on these findings, these PDX1-null patients will have additional screening to monitor the progression of metaplasia into gastric and intestinal cancer. This study further demonstrates the utility of organoids in improving patient diagnoses and treatment. Disclosure M. Krishnamurthy: None. T.R. Broda: None. D.O. Kechele: None. X. Zhang: None. J.J. Palermo: None. M.H. Collins: None. I.H. Thomas: None. A. Heider: None. A. Dauber: None. J. Wells: None. Funding American Diabetes Association (1-19-PDF-036 to M.K.)

Molecular predictors of response to selinexor in recurrent glioblastoma (GBM).

2565 Background: The nuclear export protein exportin 1 (XPO1) is overexpressed in many cancers, including GBM. Selinexor is an inhibitor of XPO1 that crosses the blood-brain-barrier and targets cancer cells by sequestering tumor suppressor proteins and oncoprotein mRNAs in the cell nucleus, inducing cancer cell apoptosis. Selinexor is FDA approved for treatment of patients (pts) with refractory multiple myeloma and is under evaluation for GBM. Methods: We previously reported encouraging results from a phase II clinical trial of selinexor for molecularly unselected pts with recurrent GBM (ASCO 2019). On available pre-treatment archival tumor tissue from 57 cases, we performed DNA exome and RNA transcriptome sequencing to use both gene mutations and expressions for exploring molecular correlates of response in selinexor treated pts, in a hypothesis generating, post-hoc, exploratory analysis. Pts with inadequate drug exposure were excluded ( &lt; 21 days or &lt; 3 doses). We compared OS and PFS between mutated and wild-type patients for genes mutated in at least 5 cases. RNAseq data were used to infer differential protein activities between patients with selinexor sensitive disease (defined as best response of partial or complete response, n = 7) vs. resistant disease (defined as progressive disease as best response, n = 23). Results: Two mutated genes were associated with longer survival in selinexor treated pts: DOCK8 (n = 7; progression free survival [PFS], P = 0.013, hazard ratio [HR] = 3.75 [1.32-10.62]; overall survival, P = 0.009, HR = 15.39 [2.00-118.34]) and PDX1 (n = 5, PFS, P = 0.014, HR = 4.468 [1.361-14.670]). Other commonly mutated genes in glioma, including IDH1 (n = 9) were observed but not associated with survival. Protein activities inferred from RNA sequencing data were also correlated with response to selinexor. In a machine learning model, ZC3H12A (also called MCPIP-1), a negative regulator of inflammation; RAB43, a member of the RAS family that binds GTP and regulates vesicle trafficking, and SOCS3, a suppressor of cytokine signaling that can antagonize JAK/STAT signaling and repress innate immunity, predicted clinical benefit from selinexor (area under the ROC curve from leave one out cross validation = 0.89, permutation test P &lt; 0.04). Conclusions: DOCK8 and PDX1 mutations were favorable prognostic factors in selinexor treated pts. Activity of three proteins (ZC3H12A, RAB43, and SOCS3) predicted clinical benefit from selinexor. Further studies with more pts are required to validate our findings. ClinicalTrials.gov: NCT01986348

184-LB: Pancreatic Hypoplasia Patients Experience Poor Weight Gain and Labile Diabetes without Diabetic Ketoacidosis (DKA)

Mutations in GATA6, GATA4 and PDX1 cause congenital diabetes and pancreatic hypoplasia (PH) or agenesis. We investigated clinical features and treatment of 10 PH patients through the University of Chicago National Monogenic Diabetes Registry. Data was self-reported or extracted from medical records. Similar to previous cohorts, congenital heart defects, gallbladder agenesis, and exocrine pancreatic insufficiency were often present, whereas features such as recurrent infections and epilepsy have not been reported previously (Figure 1). Weight gain and glycemic control were often poor, yet there were no episodes of DKA over 110 patient-years (Figure 2). Close multi-subspecialty follow-up of these complex patients may improve frequent difficulties with weight gain and highly labile blood sugars. Disclosure A.M. Denson: None. M. Freemark: Research Support; Self; Rhythm Pharmaceuticals, Inc. I.H. Thomas: None. H. Abdullatif: None. J.B. Nogueira: None. R. Benjamin: None. L.R. Letourneau: None. R.N. Naylor: None. S.W. Greeley: None. Funding American Diabetes Association (1-17-JDF-008 to S.A.W.G.); National Institutes of Health (R01DK104942, P30DK020595, UL1TR002389)

Point mutations in the PDX1 transactivation domain impair human β-cell development and function

ObjectiveHundreds of missense mutations in the coding region of PDX1 exist; however, if these mutations predispose to diabetes mellitus is unknown. MethodsIn this study, we screened a large cohort of subjects with increased risk for diabetes and identified two subjects with impaired glucose tolerance carrying common, heterozygous, missense mutations in the PDX1 coding region leading to single amino acid exchanges (P33T, C18R) in its transactivation domain. We generated iPSCs from patients with heterozygous PDX1P33T/+, PDX1C18R/+ mutations and engineered isogenic cell lines carrying homozygous PDX1P33T/P33T, PDX1C18R/C18R mutations and a heterozygous PDX1 loss-of-function mutation (PDX1+/−). ResultsUsing an in vitro β-cell differentiation protocol, we demonstrated that both, heterozygous PDX1P33T/+, PDX1C18R/+ and homozygous PDX1P33T/P33T, PDX1C18R/C18R mutations impair β-cell differentiation and function. Furthermore, PDX1+/− and PDX1P33T/P33T mutations reduced differentiation efficiency of pancreatic progenitors (PPs), due to downregulation of PDX1-bound genes, including transcription factors MNX1 and PDX1 as well as insulin resistance gene CES1. Additionally, both PDX1P33T/+ and PDX1P33T/P33T mutations in PPs reduced the expression of PDX1-bound genes including the long-noncoding RNA, MEG3 and the imprinted gene NNAT, both involved in insulin synthesis and secretion. ConclusionsOur results reveal mechanistic details of how common coding mutations in PDX1 impair human pancreatic endocrine lineage formation and β-cell function and contribute to the predisposition for diabetes.

Maturity onset diabetes of the young in India - a distinctive mutation pattern identified through targeted next-generation sequencing.

To establish and utilize a Next-Generation Sequencing (NGS)-based strategy to screen for maturity onset diabetes of the young (MODY) gene mutations in subjects with early-onset diabetes. Maturity onset diabetes of the young (MODY) genetic testing was carried out in 80 subjects of Asian Indian origin with young onset diabetes to identify mutations in a comprehensive panel of ten MODY genes. A novel multiplex polymerase chain reaction (PCR)-based target enrichment was established, followed by NGS on the Ion Torrent Personal Genome Machine (PGM). All the mutations and rare variants were confirmed by Sanger sequencing. We identified mutations in 11 (19%) of the 56 clinically diagnosed MODY subjects and seven of these mutations were novel. The identified mutations include p.H241Q, p.E59Q, c.-162G>A 5' UTR in NEUROD1, p.V169I cosegregating with c.493-4G>A and c.493-20C>T, p.E271K in HNF4A, p.A501S in HNF1A, p.E440X in GCK, p.V177M in PDX1, p.L92F in HNF1B and p.R31L in PAX4 genes. Interestingly, two patients with NEUROD1 mutation were also positive for the p.E224K mutation in PDX1 gene. These patients with coexisting NEUROD1-PDX1 mutations showed a marked reduction in glucose-induced insulin secretion. All 24 subjects who had not met the clinical criteria of MODY were negative for the mutations. To the best of our knowledge, this is the first report of PDX1, HNF1B, NEUROD1 and PAX4 mutations from India. Multiplex PCR coupled with NGS provides a rapid, cost-effective and accurate method for comprehensive parallelized genetic testing of MODY. When compared to earlier reports, we have identified a higher frequency and a novel digenic mutation pattern involving NEUROD1 and PDX1 genes.

A novel GATA6 mutation leading to congenital heart defects and permanent neonatal diabetes: A case report

Permanent neonatal diabetes mellitus is a rare condition mostly due to heterozygous mutations in the KCNJ11, ABCC8 and INS genes. Neonatal diabetes due to pancreatic agenesis is extremely rare. Mutations in PDX1, PTF1A, HNF1B, EIF2AK3, RFX6 and GATA6 genes have been shown to result in pancreatic agenesis or hypoplasia. This report describes a 40-day-old male infant diagnosed with permanent neonatal diabetes associated with atrial septal defect, pulmonary stenosis, patent ductus arteriosus and a novel de novo heterozygous missense mutation (p.N466S) in the GATA6 gene with no evidence of exocrine pancreas insufficiency. In addition to permanent neonatal diabetes, the patient had transient idiopathic neonatal cholestasis and hypoglycaemic episodes unrelated to insulin treatment, features that are rarely described in children with permanent neonatal diabetes.

Control of Cell Identity in Pancreas Development and Regeneration

The endocrine and exocrine cells in the adult pancreas are not static, but can change their differentiation state in response to injury or stress. This concept of cells in flux means that there may be ways to generate certain types of cells (such as insulin-producing β-cells) and prevent formation of others (such as transformed neoplastic cells). We review different aspects of cell identity in the pancreas, discussing how cells achieve their identity during embryonic development and maturation, and how this identity remains plastic, even in the adult pancreas.

Biallelic PDX1 (insulin promoter factor 1) mutations causing neonatal diabetes without exocrine pancreatic insufficiency.

AimsRecessive PDX1 (IPF1) mutations are a rare cause of pancreatic agenesis, with three cases reported worldwide. A recent report described two cousins with a homozygous hypomorphic PDX1 mutation causing permanent neonatal diabetes with subclinical exocrine insufficiency. The aim of our study was to investigate the possibility of hypomorphic PDX1 mutations in a large cohort of patients with permanent neonatal diabetes and no reported pancreatic hypoplasia or exocrine insufficiency.MethodsPDX1 was sequenced in 103 probands with isolated permanent neonatal diabetes in whom ABCC8, KCNJ11 and INS mutations had been excluded.ResultsSequencing analysis identified biallelic PDX1 mutations in three of the 103 probands with permanent neonatal diabetes (2.9%). One proband and his affected brother were compound heterozygotes for a frameshift and a novel missense mutation (p.A34fsX191; c.98dupC and p.P87L; c.260C>T). The other two probands were homozygous for novel PDX1 missense mutations (p.A152G; c.455C>G and p.R176Q; c.527G>A). Both mutations affect highly conserved residues located within the homeobox domain. None of the four cases showed any evidence of exocrine pancreatic insufficiency, either clinically, or, where data were available, biochemically. In addition a heterozygous nonsense mutation (p.C18X; c.54C>A) was identified in a fourth case.ConclusionsThis study demonstrates that recessive PDX1 mutations are a rare but important cause of isolated permanent neonatal diabetes in patients without pancreatic hypoplasia/agenesis. Inclusion of the PDX1 gene in mutation screening for permanent neonatal diabetes is recommended as a genetic diagnosis reveals the mode of inheritance, allows accurate estimation of recurrence risks and confirms the requirement for insulin treatment.

Research Resource: The Pdx1 Cistrome of Pancreatic Islets

The homeodomain transcription factor pancreas duodenal homeobox 1 (Pdx1, also known as insulin promoter factor 1) is a master regulator of pancreas development, as mice or humans lacking Pdx1 function are a pancreatic. Importantly, heterozygous mutations in Pdx1 cause early and late onset forms of diabetes in humans. Despite these central roles in development and adult β-cell function, we have only rudimentary knowledge of the transcriptome targets of Pdx1 that mediate these phenotypes. Therefore, we performed global location analysis of Pdx1 occupancy in pancreatic islets. We used evolutionary conservation of target genes to identify the most relevant Pdx1 targets by performing chromatin immunoprecipitation sequencing on both human and mouse islets. Remarkably, the conserved target set is highly enriched for genes annotated to function in endocrine system and metabolic disorders, various signaling pathways, and cell survival, providing a molecular explanation for many of the phenotypes resulting from Pdx1 deficiency.

GATA6 haploinsufficiency causes pancreatic agenesis in humans.

Understanding the regulation of pancreatic development is key for efforts to develop new regenerative therapeutic approaches for diabetes. Rare mutations in PDX1 and PTF1A can cause pancreatic agenesis, however, most instances of this disorder are of unknown origin. We report de novo heterozygous inactivating mutations in GATA6 in 15/27 (56%) individuals with pancreatic agenesis. These findings define the most common cause of human pancreatic agenesis and establish a key role for the transcription factor GATA6 in human pancreatic development.

The role of pancreatic imaging in monogenic diabetes mellitus

In neonatal diabetes mellitus resulting from mutations in EIF2AK3, PTF1A, HNF1B, PDX1 or RFX6, pancreatic aplasia or hypoplasia is typical. In maturity-onset diabetes mellitus of the young (MODY), mutations in HNF1B result in aplasia of pancreatic body and tail, and mutations in CEL lead to lipomatosis. The pancreas is not readily accessible for histopathological investigations and pancreatic imaging might, therefore, prove important for diagnosis, treatment, and research into these β-cell diseases. Advanced imaging techniques can identify the pancreatic features that are characteristic of inherited diabetes subtypes, including alterations in organ size (diffuse atrophy and complete or partial pancreatic agenesis), lipomatosis and calcifications. Consequently, in patients with suspected monogenic diabetes mellitus, the results of pancreatic imaging could help guide the molecular and genetic investigation. Imaging findings also highlight the critical roles of specific genes in normal pancreatic development and differentiation and provide new insight into alterations in pancreatic structure that are relevant for β-cell disease.

Who should have genetic testing for maturity‐onset diabetes of the young?

Maturity-onset diabetes of the young (MODY) is a clinically heterogeneous group of monogenic disorders characterized by autosomal dominant inheritance of young-onset, non-insulin-dependent diabetes. The genes involved are important in beta cell development, function and regulation and lead to disorders in glucose sensing and insulin secretion. Heterozygous GCK mutations cause impaired glucokinase activity resulting in stable, mild hyperglycaemia that rarely requires treatment. HNF1A mutations cause a progressive insulin secretory defect that is sensitive to sulphonylureas, most often resulting in improved glycaemic control compared with other diabetes treatment. MODY owing to mutations in the HNF4A gene results in a similar phenotype, including sensitivity to sulphonylurea treatment. HNF1B mutations most frequently cause developmental renal disease (particularly renal cysts) but may also cause MODY in isolation or may cause the renal cysts and diabetes syndrome (RCAD syndrome). Mutations in NEUROD1, PDX1 (IPF1), CEL and INS are rare causes of MODY. MODY is often misdiagnosed as type 1 or type 2 diabetes. However, a correct genetic diagnosis impacts treatment and identifies at-risk family members. Thus, it is important to consider a diagnosis of MODY in appropriate individuals and to pursue genetic testing to establish a molecular diagnosis.

Pcif1 modulates Pdx1 protein stability and pancreatic β cell function and survival in mice

The homeodomain transcription factor pancreatic duodenal homeobox 1 (Pdx1) is a major mediator of insulin transcription and a key regulator of the β cell phenotype. Heterozygous mutations in PDX1 are associated with the development of diabetes in humans. Understanding how Pdx1 expression levels are controlled is therefore of intense interest in the study and treatment of diabetes. Pdx1 C terminus-interacting factor-1 (Pcif1, also known as SPOP) is a nuclear protein that inhibits Pdx1 transactivation. Here, we show that Pcif1 targets Pdx1 for ubiquitination and proteasomal degradation. Silencing of Pcif1 increased Pdx1 protein levels in cultured mouse β cells, and Pcif1 heterozygosity normalized Pdx1 protein levels in Pdx1(+/-) mouse islets, thereby increasing expression of key Pdx1 transcriptional targets. Remarkably, Pcif1 heterozygosity improved glucose homeostasis and β cell function and normalized β cell mass in Pdx1(+/-) mice by modulating β cell survival. These findings indicate that in adult mouse β cells, Pcif1 limits Pdx1 protein accumulation and thus the expression of insulin and other gene targets important in the maintenance of β cell mass and function. They also provide evidence that targeting the turnover of a pancreatic transcription factor in vivo can improve glucose homeostasis.