Complete glucokinase deficiency is not a common cause of permanent neonatal diabetes

Management of monogenic diabetes in pregnancy: A narrative review

Pregnancy in women with monogenic diabetes is potentially complex, with significant implications for both maternal and fetal health. Among these, maturity-onset diabetes of the young (MODY) stands out as a prevalent monogenic diabetes subtype frequently encountered in clinical practice. Each subtype of MODY requires a distinct approach tailored to the pregnancy, diverging from management strategies in non-pregnant individuals. Glucokinase MODY (GCK-MODY) typically does not require treatment outside of pregnancy, but special considerations arise when a woman with GCK-MODY becomes pregnant. The glycemic targets in GCK-MODY pregnancies are not exclusively dictated by the maternal/paternal MODY genotype but are also influenced by the genotype of the developing fetus. During pregnancy, the choice between sulfonylurea or insulin for treating hepatocyte nuclear factor 1-alpha (HNF1A)-MODY and HNF4A-MODY depends on the mother's specific circumstances and the available expertise. Management of other rarer MODY subtypes is individualized, with decisions made on a case-by-case basis. Therefore, a collaborative approach involving expert diabetes and obstetric teams is crucial for the comprehensive management of MODY pregnancies.

Variable presentations of GCK gene mutation in a family

We describe siblings born from non-consanguineous parents, with older sibling having asymptomatic hyperglycaemia while younger sibling presented with low birth weight and persistent hyperglycaemia from first month of life. Our case, the older sibling was heterozygous for paternally inherited GCK pathogenic variant resulting in diabetes of maturity-onset in the young (MODY) manifested as mild fasting hyperglycaemia. GCK gene sequencing revealed that the younger sibling was compound heterozygous for missense mutations (two) combined in a novel GCK-permanent neonatal diabetes mellitus (PNDM) genotype. Thus, heterozygous inactivating GCK mutations are likely to lead to maturity-onset diabetes of the young type 2 (MODY 2) and the homozygous inactivating or compound heterozygous GCK mutations are a cause of PNDM.

Clinical implications of the glucokinase impaired function - GCK MODY today

Heterozygous inactivating mutations of the glucokinase (GCK) gene are causing GCK-MODY, one of the most common forms of the Maturity Onset Diabetes of the Young (MODY). GCK-MODY is characterized by fasting hyperglycemia without apparent worsening with aging and low risk for chronic vascular complications. Despite the mild clinical course, GCK-MODY could be misdiagnosed as type 1 or type 2 diabetes. In the diagnostic process, the clinical suspicion is often based on the clinical diagnostic criteria for GCK-MODY and should be confirmed by DNA analysis. However, there are several issues in the clinical and also in genetic part that could complicate the diagnostic process. Most of the people with GCK-MODY do not require any pharmacotherapy. The exception are pregnant women with a fetus which did not inherit GCK mutation from the mother. Such a child has accelerated growth, and has increased risk for diabetic foetopathy. In this situation the mother should be treated with substitutional doses of insulin. Therefore, distinguishing GCK-MODY from gestational diabetes in pregnancy is very important. For this purpose, special clinical diagnostic criteria for clinical identification of GCK-MODY in pregnancy are used. This review updates information on GCK-MODY and discusses several currently not solved problems in the clinical diagnostic process, genetics, and treatment of this type of monogenic diabetes.

Neonatal Diabetes Mellitus

Neonatal Diabetes (ND) mellitus is a rare genetic disease (1 in 90,000 live births). It is defined by the presence of severe hyperglycaemia associated with insufficient or no circulating insulin, occurring mainly before 6 months of age and rarely between 6 months and 1 year. Such hyperglycaemia requires either transient treatment with insulin in about half of cases, or permanent insulin treatment. The disease is explained by two major groups of mechanism: malformation of the pancreas with altered insulin-secreting cells development/survival or abnormal function of the existing pancreatic β cell. The most frequent genetic causes of neonatal diabetes mellitus with abnormal β cell function are abnormalities of the 6q24 locus and mutations of the ABCC8 or KCNJ11 genes coding for the potassium channel in the pancreatic β cell. Other genes are associated with pancreas malformation or insufficient β cells development or destruction of β cells. Clinically, compared to patients with an ABCC8 or KCNJ11 mutation, patients with a 6q24 abnormality have lower birth weight and height, are younger at diagnosis and remission, and have a higher malformation frequency. Patients with an ABCC8 or KCNJ11 mutation have neurological and neuropsychological disorders in all those tested carefully. Up to 86% of patients who go into remission have recurrent diabetes when they reach puberty, with no difference due to the genetic origin. All these results reinforce the importance of prolonged follow-up by a multidisciplinary pediatric team, and later doctors specializing in adult medicine. 90% of the patients with an ABCC8 or KCNJ11 mutation as well as those with 6q24 anomalies are amenable to a successful switch from insulin injection to oral sulfonylureas.

Clinical characteristics and molecular genetic analysis of 22 patients with neonatal diabetes from the South-Eastern region of Turkey: predominance of non-KATP channel mutations

BACKGROUND

Neonatal diabetes mellitus (NDM) is a rare form of monogenic diabetes and usually presents in the first 6 months of life. We aimed to describe the clinical characteristics and molecular genetics of a large Turkish cohort of NDM patients from a single centre and estimate an annual incidence rate of NDM in South-Eastern Anatolian region of Turkey.

DESIGN AND METHODS

NDM patients presenting to Diyarbakir Children State Hospital between 2010 and 2013, and patients under follow-up with presumed type 1 diabetes mellitus, with onset before 6 months of age were recruited. Molecular genetic analysis was performed.

RESULTS

Twenty-two patients (59% males) were diagnosed with NDM (TNDM-5; PNDM-17). Molecular genetic analysis identified a mutation in 20 (95%) patients who had undergone a mutation analysis. In transient neonatal diabetes (TNDM) patients, the genetic cause included chromosome 6q24 abnormalities (n=3), ABCC8 (n=1) and homozygous INS (n=1). In permanent neonatal diabetes (PNDM) patients, homozygous GCK (n=6), EIF2AK3 (n=3), PTF1A (n=3), and INS (n=1) and heterozygous KCNJ11 (n=2) mutations were identified. Pancreatic exocrine dysfunction was observed in patients with mutations in the distal PTF1A enhancer. Both patients with a KCNJ11 mutation responded to oral sulphonylurea. A variable phenotype was associated with the homozygous c.-331C>A INS mutation, which was identified in both a PNDM and TNDM patient. The annual incidence of PNDM in South-East Anatolian region of Turkey was one in 48 000 live births.

CONCLUSIONS

Homozygous mutations in GCK, EIF2AK3 and the distal enhancer region of PTF1A were the commonest causes of NDM in our cohort. The high rate of detection of a mutation likely reflects the contribution of new genetic techniques (targeted next-generation sequencing) and increased consanguinity within our cohort.

A new compound heterozygosis for inactivating mutations in the glucokinase gene as cause of permanent neonatal diabetes mellitus (PNDM) in double-first cousins

BACKGROUND

Permanent neonatal diabetes mellitus (PNDM) is a rare disorder, characterized by uncontrolled hyperglycemia diagnosed during the first 6 months of life. In general, PNDM has a genetic origin and most frequently it results from heterozygous mutations in KCNJ11, INS and ABCC8 genes. Homozygous or compound heterozygous inactivating mutations in GCK gene as cause of PNDM are rare. In contrast, heterozygosis for GCK inactivating mutations is frequent and results in the maturity-onset diabetes of young (MODY), manifested by a mild fasting hyperglycemia usually detected later in life. Therefore, as an autosomal recessive disorder, GCK-PNDM should be considered in families with history of glucose intolerance or MODY in first relatives, especially when consanguinity is suspected.

RESULTS

Here we describe two patients born from non-consanguineous parents within a family. They presented low birth weight with persistent hyperglycemia during the first month of life. Molecular analyses for KCNJ11, INS, ABCC8 did not show any mutation. GCK gene sequencing, however, revealed that both patients were compound heterozygous for two missense combined in a novel GCK-PNDM genotype. The p.Asn254His and p.Arg447Gly mutations had been inherited from their mothers and fathers, respectively, as their mothers are sisters and their fathers are brothers. Parents had been later diagnosed as having GCK-MODY.

CONCLUSIONS

Mutations' in silico analysis was carried out to elucidate the role of the amino acid changes on the enzyme structure. Both p.Asn254His and p.Arg447Gly mutations appeared to be quite damaging. This is the first report of GCK-PNDM in a Brazilian family.

[Early onset diabetes mellitus]

Neonatal diabetes mellitus is a rare condition (1/90,000 to 1/260,000 live births) defined as mild-to-severe hyperglycemia within the first year of life. Permanent neonatal diabetes mellitus requires lifelong therapy, whereas transient form resolves early in life but may relapse later on. Two main physiopathological mechanisms may explain this disease: β cell functional impairment or absence (pancreas agenesis or β cells destruction). The main genetic causes of β cells impairment are 6q24 abnormalities and mutations in ABCC8 or KCNJ11 potassium channel (KATP channel) genes. Compared to the KATP subtype, the 6q24 subtype had specific features: developmental defects involving the heart, kidneys, or urinary tract, intrauterine growth restriction, and early diagnosis. Remission of neonatal diabetes mellitus occurred in 51% of probands at a median age of 17 weeks. Recurrence was common at pubertal age, with no difference between the 6q24 and KATP-channel groups (82% vs 86%, p=0.36, respectively). Patients with mutations in ABCC8 or KCNJ11 genes had developmental delay with or without epilepsy but also developmental coordination disorder (particularly visual-spatial dyspraxia) or attention deficits in all of those who underwent in-depth neuropsychomotor investigations.

Mutations in pancreatic ß-cell Glucokinase as a cause of hyperinsulinaemic hypoglycaemia and neonatal diabetes mellitus

Glucokinase is a key enzyme involved in regulating insulin secretion from the pancreatic ß-cell. The unique role of glucokinase in human glucose physiology is illustrated by the fact that genetic mutations in glucokinase can either cause hyperglycaemia or hypoglycaemia. Heterozygous inactivating mutations in glucokinase cause maturity-onset diabetes of the young (MODY), homozygous inactivating in glucokinase mutations result in permanent neonatal diabetes whereas heterozygous activating glucokinase mutations cause hyperinsulinaemic hypoglycaemia.

Update on mutations in glucokinase (GCK), which cause maturity-onset diabetes of the young, permanent neonatal diabetes, and hyperinsulinemic hypoglycemia

Glucokinase is a key regulatory enzyme in the pancreatic beta-cell. It plays a crucial role in the regulation of insulin secretion and has been termed the glucose sensor in pancreatic beta-cells. Given its central role in the regulation of insulin release it is understandable that mutations in the gene encoding glucokinase (GCK) can cause both hyper- and hypoglycemia. Heterozygous inactivating mutations in GCK cause maturity-onset diabetes of the young (MODY) subtype glucokinase (GCK), characterized by mild fasting hyperglycemia, which is present at birth but often only detected later in life during screening for other purposes. Homozygous inactivating GCK mutations result in a more severe phenotype presenting at birth as permanent neonatal diabetes mellitus (PNDM). A growing number of heterozygous activating GCK mutations that cause hypoglycemia have also been reported. A total of 620 mutations in the GCK gene have been described in a total of 1,441 families. There are no common mutations, and the mutations are distributed throughout the gene. The majority of activating mutations cluster in a discrete region of the protein termed the allosteric activator site. The identification of a GCK mutation in patients with both hyper- and hypoglycemia has implications for the clinical course and clinical management of their disorder.

Hyperinsulinism and diabetes: genetic dissection of beta cell metabolism-excitation coupling in mice

The role of metabolism-excitation coupling in insulin secretion has long been apparent, but in recent years, in parallel with studies of human hyperinsulinism and diabetes, genetic manipulation of proteins involved in glucose transport, metabolism, and excitability in mice has brought the central importance of this pathway into sharp relief. We focus on these animal studies and how they provide important insights into not only metabolic and electrical regulation of insulin secretion, but also downstream consequences of alterations in this pathway and the etiology and treatment of insulin-secretion diseases in humans.

Neonatal hyperglycaemia and abnormal development of the pancreas

Transient and permanent neonatal diabetes mellitus (TNDM and PNDM) are rare conditions occurring in around 1 per 300,000 live births. In TNDM, growth-retarded infants develop diabetes in the first few weeks of life, only to go into remission after a few months with possible relapse to permanent diabetes usually around adolescence or in adulthood. In PNDM, insulin secretory failure occurs in the late fetal or early postnatal period. The very recently elucidated mutations in KCNJ11 and ABCC8 genes, encoding the Kir6.2 and SUR1 subunits of the pancreatic K(ATP) channel involved in regulation of insulin secretion, account for a third to a half of the PNDM cases. Molecular analysis of chromosome 6 anomalies and the KCNJ11 and ABCC8 genes encoding Kir6.2 and SUR1 provides a tool for distinguishing transient from permanent neonatal diabetes mellitus in the neonatal period. Some patients (those with mutations in KCNJ11 and ABCC8) may be transferred from insulin therapy to sulphonylureas.

[Neonatal diabetes: a disease linked to multiple mechanisms]

Transient (TNDM) and Permanent (PNDM) Neonatal Diabetes Mellitus are rare conditions occurring in about 1: 300,000 live births. In TNDM growth retarded infants develop diabetes in the first few weeks of life only to go into remission in a few months with possible relapse to a permanent diabetes state usually around adolescence or as adults. We believe that pancreatic dysfunction in this condition is maintained throughout life with relapse initiated at times of metabolic stress such as puberty or pregnancy. In PNDM, insulin secretory failure occurs in the late fetal or early postnatal period. A number of conditions are associated with PNDM, some of which have been elucidated at the molecular levels. Among those, the very recently elucidated mutations in KCNJ11 and ABCC8 gene, encoding the Kir6.2 and SUR1 subunit of the pancreatic K(ATP) channel involved in regulation of insulin secretion accounts for one third to a half of the PNDM cases. Patients with TNDM are more likely to have intrauterine growth retardation and less likely to develop ketoacidosis than patients with PNDM. In TNDM, patients are younger at the diagnosis of diabetes and have lower initial insulin requirements. Considerable overlap occurs between the two groups, so that TNDM cannot be distinguished from PNDM based on clinical features. Very early onset diabetes mellitus seems to be unrelated to autoimmunity in most instances. Recurrent diabetes is common in patients with "transient" neonatal diabetes mellitus and, consequently, prolonged follow-up is imperative. Molecular analysis of chromosome 6 anomalies, the KCNJ11 and ABCC8 genes encoding Kir6.2 and SUR1 provide a tool to identify transient from permanent neonatal diabetes mellitus in the neonatal period. This analysis also has potentially important therapeutic consequences leading to transfer some patients, those with mutations in KCNJ11 and ABCC8 from insulin therapy to sulfonylureas. Realizing how difficult it is to take care of a child of this age with diabetes mellitus should prompt clinicians to transfer these children to specialized centers. Insulin therapy and high caloric intake are the basis of the treatment. Insulin pump may offer an interesting therapeutic tool in this age group in experienced hands.

Defining the genetic aetiology of monogenic diabetes can improve treatment

A molecular genetic diagnosis is now possible for > 80% of patients with monogenic diabetes. This not only provides accurate information regarding inheritance and prognosis, but can inform treatment decisions and improve clinical outcome. Mild fasting hyperglycaemia caused by heterozygous GCK mutations rarely requires pharmacological intervention, whereas patients with mutations in the genes encoding the transcription factors HNF-1alpha and HNF-4alpha respond well to low doses of sulphonylureas. The recent discovery that mutations in the KCNJ11 gene (encoding the Kir6.2 subunit of the K(ATP) channel) are the most common cause of permanent neonatal diabetes, has enabled children to stop insulin injections and achieve improved glycaemic control with high doses of sulphonylurea tablets. Molecular genetic testing is an essential prerequisite for the pharmacogenetic treatment of monogenic diabetes.

Neonatal diabetes mellitus: a disease linked to multiple mechanisms

Transient (TNDM) and Permanent (PNDM) Neonatal Diabetes Mellitus are rare conditions occurring in 1:300,000-400,000 live births. TNDM infants develop diabetes in the first few weeks of life but go into remission in a few months, with possible relapse to a permanent diabetes state usually around adolescence or as adults. The pancreatic dysfunction in this condition may be maintained throughout life, with relapse initiated at times of metabolic stress such as puberty or pregnancy. In PNDM, insulin secretory failure occurs in the late fetal or early post-natal period and does not go into remission. Patients with TNDM are more likely to have intrauterine growth retardation and less likely to develop ketoacidosis than patients with PNDM. In TNDM, patients are younger at the diagnosis of diabetes and have lower initial insulin requirements. Considerable overlap occurs between the two groups, so that TNDM cannot be distinguished from PNDM based on clinical features. Very early onset diabetes mellitus seems to be unrelated to autoimmunity in most instances. A number of conditions are associated with PNDM, some of which have been elucidated at the molecular level. Among these, the very recently elucidated mutations in the KCNJ11 and ABCC8 genes, encoding the Kir6.2 and SUR1 subunit of the pancreatic KATP channel involved in regulation of insulin secretion, account for one third to half of the PNDM cases. Molecular analysis of chromosome 6 anomalies (found in more than 60% in TNDM), and the KCNJ11 and ABCC8 genes encoding Kir6.2 and SUR1, provides a tool to identify TNDM from PNDM in the neonatal period. This analysis also has potentially important therapeutic consequences leading to transfer some patients, those with mutations in KCNJ11 and ABCC8 genes, from insulin therapy to sulfonylureas. Recurrent diabetes is common in patients with "transient" neonatal diabetes mellitus and, consequently, prolonged follow-up is imperative. Realizing how difficult it is to take care of a child of this age with diabetes mellitus should prompt clinicians to transfer these children to specialized centers. Insulin therapy and high caloric intake are the basis of the treatment. Insulin pump may offer an interesting therapeutic tool in this age group in experienced hands.

Neonatal diabetes: how research unravelling the genetic puzzle has both widened our understanding of pancreatic development whilst improving children's quality of life

It has become increasingly apparent over the last few years that the seemingly ubiquitous auto-immune aetiology to pre-pubertal diabetes does not apply to those diagnosed under 6 months of age. In this age group, disease appears, in the vast majority of cases, to be conferred by single gene disorders mainly related to pancreatic development. The unravelling of these disorders has resulted in a far greater understanding of pancreatic development and some startling changes in treatment, resulting in improved quality of life and diabetes control. The progress made in our scientific and clinical understanding of these extremely rare diseases is a perfect example of how studying seemingly rare illnesses can improve our overall knowledge of much more common conditions.

ATP-sensitive potassium channelopathies: focus on insulin secretion

ATP-sensitive potassium (K(ATP)) channels, so named because they are inhibited by intracellular (ATP), play key physiological roles in many tissues. In pancreatic beta cells, these channels regulate glucose-dependent insulin secretion and serve as the target for sulfonylurea drugs used to treat type 2 diabetes. This review focuses on insulin secretory disorders, such as congenital hyperinsulinemia and neonatal diabetes, that result from mutations in K(ATP) channel genes. It also considers the extent to which defective regulation of K(ATP) channel activity contributes to the etiology of type 2 diabetes.

ATP-sensitive K+ channel signaling in glucokinase-deficient diabetes

As the rate-limiting controller of glucose metabolism, glucokinase represents the primary beta-cell "glucose sensor." Inactivation of both glucokinase (GK) alleles results in permanent neonatal diabetes; inactivation of a single allele causes maturity-onset diabetes of the young type 2 (MODY-2). Similarly, mice lacking both alleles (GK(-/-)) exhibit severe neonatal diabetes and die within a week, whereas heterozygous GK(+/-) mice exhibit markedly impaired glucose tolerance and diabetes, resembling MODY-2. Glucose metabolism increases the cytosolic [ATP]-to-[ADP] ratio, which closes ATP-sensitive K(+) channels (K(ATP) channels), leading to membrane depolarization, Ca(2+) entry, and insulin exocytosis. Glucokinase insufficiency causes defective K(ATP) channel regulation, which may underlie the impaired secretion. To test this prediction, we crossed mice lacking neuroendocrine glucokinase (nGK(+/-)) with mice lacking K(ATP) channels (Kir6.2(-/-)). Kir6.2 knockout rescues perinatal lethality of nGK(-/-), although nGK(-/-)Kir6.2(-/-) animals are postnatally diabetic and still die prematurely. nGK(+/-) animals are diabetic on the Kir6.2(+/+) background but only mildly glucose intolerant on the Kir6.2(-/-) background. In the presence of glutamine, isolated nGK(+/-)Kir6.2(-/-) islets show improved insulin secretion compared with nGK(+/-)Kir6.2(+/+). The significant abrogation of nGK(-/-) and nGK(+/-) phenotypes in the absence of K(ATP) demonstrate that a major factor in glucokinase deficiency is indeed altered K(ATP) signaling. The results have implications for understanding and therapy of glucokinase-related diabetes.

Diagnosis and Management of Maturity-Onset Diabetes of the Young

Maturity-onset diabetes of the young (MODY) is a dominantly inherited form of non-ketotic diabetes mellitus. It results from a primary defect of insulin secretion, and usually develops at childhood, adolescence, or young adulthood. MODY is a heterogeneous disease with regard to genetic, metabolic, and clinical features. All MODY genes have not been identified, but heterozygous mutations in six genes cause the majority of the MODY cases. By far MODY2 (due to mutations of the glucokinase gene) and MODY3 (due to mutations in hepatocyte nuclear factor-1alpha) are the most frequent. As with MODY3, all the other MODY subtypes are associated with mutations in transcription factors. The clinical presentations of the different MODY subtypes differ, particularly in the severity and the course of the insulin secretion defect, the risk of microvascular complications of diabetes, and the defects associated with diabetes. Patients with MODY2 have mild, asymptomatic, and stable hyperglycemia that is present from birth. They rarely develop microvascular disease, and seldom require pharmacologic treatment of hyperglycemia. In patients with MODY3, severe hyperglycemia usually occurs after puberty, and may lead to the diagnosis of type 1 diabetes. Despite the progression of insulin defects, sensitivity to sulfonylureas may be retained in MODY3 patients. Diabetic retinopathy and nephropathy frequently occur in patients with MODY3, making frequent follow-up mandatory. By contrast, other risk factors are not present in patients with MODY and the frequency of cardiovascular disease is not increased. The clinical spectrum of MODY is wider than initially described, and might include multi-organ involvement in addition to diabetes. In patients with MODY5, due to mutations in hepatocyte nuclear factor-1beta, diabetes is associated with pancreatic atrophy, renal morphologic and functional abnormalities, and genital tract and liver test abnormalities. Although MODY is dominantly inherited, penetrance or expression of the disease may vary and a family history of diabetes is not always present. Thus, the diagnosis of MODY should be raised in various clinical circumstances. Molecular diagnosis has important consequences in terms of prognosis, family screening, and therapy.

Permanent neonatal diabetes in an Asian infant

We describe a novel homozygous missense glucokinase mutation (R397L) resulting in insulin-treated neonatal diabetes in an infant from a consanguineous Asian family. Both parents were heterozygous for R397L and had mild hyperglycemia. Glucokinase mutations should be considered in infants of all ethnic groups with neonatal diabetes and consanguinity.

Neonatal diabetes, with hypoplastic pancreas, intestinal atresia and gall bladder hypoplasia: search for the aetiology of a new autosomal recessive syndrome

AIMS/HYPOTHESIS

Neonatal diabetes is a rare disease with several identified molecular aetiologies. Despite associations with other malformations, neonatal diabetes with intestinal and biliary anomalies has not been described. The current study aims to describe a new syndrome, and to examine a possible link with one of three genes known to cause neonatal diabetes.

METHODS

Five clinical cases are described. Immunohistochemical staining for pancreatic islet hormones was performed on three of the infants. DNA from one infant was analysed for abnormalities of the PLAGL-1 (ZAC), glucokinase and PDX-1 (IPF-1) genes.

RESULTS

Five infants (two sibling pairs from two families, and an isolated case) presented with neonatal diabetes, hypoplastic or annular pancreas, jejunal atresia, duodenal atresia and gall bladder aplasia or hypoaplasia. One sibling pair was born to consanguineous parents. One patient with a milder form is surviving free of insulin. Four children died in the first year of life despite aggressive medical management. Pancreatic immunohistochemistry revealed few scattered chromogranin-A-positive cell clusters but complete absence of insulin, glucagon and somatostatin. Exocrine histology was variable. In one case from the consanguineous family, molecular analysis showed no duplication or uniparental isodisomy of PLAGL-1 at 6q24, no contiguous gene deletion involving the glucokinase gene, and no mutation in the coding sequences or splice sites of PDX-1.

CONCLUSIONS/INTERPRETATION

This combination of multiple congenital abnormalities has not been previously described and probably represents a new autosomal recessive syndrome involving a genetic abnormality that interferes with normal islet development and whose aetiology is as yet unknown.

Glucokinase (GCK) mutations in hyper- and hypoglycemia: maturity-onset diabetes of the young, permanent neonatal diabetes, and hyperinsulinemia of infancy

Glucokinase is a key regulatory enzyme in the pancreatic beta-cell. It plays a crucial role in the regulation of insulin secretion and has been termed the pancreatic beta-cell sensor. Given its central role in the regulation of insulin release, it is understandable that mutations in the gene encoding glucokinase (GCK) can cause both hyperglycemia and hypoglycemia. Heterozygous inactivating mutations in GCK cause maturity-onset diabetes of the young (MODY), characterized by mild hyperglycemia, which is present at birth, but is often only detected later in life during screening for other purposes. Homozygous inactivating GCK mutations result in a more severe phenotype, presenting at birth as permanent neonatal diabetes mellitus (PNDM). Several heterozygous activating GCK mutations that cause hypoglycemia have also been reported. A total of 195 mutations in the GCK gene have been described, in a total of 285 families. There are no common mutations and the mutations are distributed throughout the gene. Mutations that cause hypoglycemia are located in various exons in a discrete region of the protein termed the heterotropic allosteric activator site. The identification of a GCK mutation in hyper- and hypoglycemia has implications for the clinical course and clinical management of the disorder.

Neonatal and very-early-onset diabetes mellitus

Transient (TNDM) and permanent neonatal diabetes mellitus (PNDM) are rare conditions occurring in one in 400,000-500,000 live births. In TNDM, growth-retarded infants develop diabetes in the first few weeks of life only to go into remission in a few months with later relapse as permanent type 2 diabetes, often around the time of adolescence. We believe that pancreatic dysfunction in this condition is maintained throughout life with relapse initiated at times of metabolic stress such as puberty or pregnancy. The mechanisms involved in this rare condition may inform on fetal pancreatic development, islet cell physiology and predisposition to type 2 diabetes. In PNDM, insulin secretory failure occurs in the early postnatal period. A number of conditions are associated with PNDM, some of which have been elucidated at the molecular level. Insulin therapy is difficult to manage in the neonatal period, and in experienced hands, the insulin pump may provide a valuable tool to administer insulin.

Permanent neonatal diabetes caused by glucokinase deficiency: inborn error of the glucose-insulin signaling pathway

Neonatal diabetes can be either permanent or transient. We have recently shown that permanent neonatal diabetes can result from complete deficiency of glucokinase activity. Here we report three new cases of glucokinase-related permanent neonatal diabetes. The probands had intrauterine growth retardation (birth weight <1,900 g) and insulin-treated diabetes from birth (diagnosis within the first week of life). One of the subjects was homozygous for the missense mutation Ala378Val (A378V), which is an inactivating mutation with an activity index of only 0.2% of wild-type glucokinase activity. The second subject was homozygous for a mutation in the splice donor site of exon 8 (intervening sequence 8 [IVS8] + 2T-->G), which is predicted to lead to the synthesis of an inactive protein. The third subject (second cousin of subject 2) was a compound heterozygote with one allele having the splice-site mutation IVS8 + 2T-->G and the other the missense mutation Gly264Ser (G264S), a mutation with an activity index of 86% of normal activity. The five subjects with permanent neonatal diabetes due to glucokinase deficiency identified to date are characterized by intrauterine growth retardation, permanent insulin-requiring diabetes from the first day of life, and hyperglycemia in both parents. Autosomal recessive inheritance and enzyme deficiency are features typical for an inborn error of metabolism, which occurred in the glucose-insulin signaling pathway in these subjects.