Neonatal Diabetes Mellitus Due to Complete Glucokinase Deficiency

Abstract

IABETES mellitus is a heterogeneous disorder that can occur at any age. 1 Neonatal diabetes mellitus, defined as insulin-requiring hyperglycemia within the first month of life, is a rare disorder that is usually associated with intrauterine growth retardation. 2 Like diabetes in general, neonatal diabetes is heterogeneous and can be either transient or permanent. Transient neonatal diabetes is associated with abnormalities of chromosome 6, 2,3 whereas mutations in insulin promoter factor 1 result in pan-creatic agenesis and permanent neonatal diabetes. 4 We describe two patients in whom complete deficiency of the glycolytic enzyme glucokinase, a key regulator of glucose metabolism in pancreatic beta cells that couples extracellular glucose to insulin secretion, caused permanent neonatal diabetes. 5 CASE REPORTS Subject 1 A baby girl of Norwegian ancestry was delivered by cesarean section at 36 weeks' gestation (birth weight, 1670 g; length, 42 cm) because of poor fetal growth (Subject III-7 in Family 1 in Fig. 1). 6 Her parents were first cousins, and both had glucose intolerance. In addition to being small for gestational age (less than the 3rd per-centile), the infant had total situs inversus. On the first day of life, her blood glucose concentration was 145 mg per deciliter (8.1 mmol per liter), and on day 2 it was 300 mg per deciliter (17 mmol D per liter), at which time treatment with insulin was started. The initial insulin requirement was 0.75 U per kilogram of body weight per day. Blood glucose control was difficult to achieve, and there were large variations in blood glucose concentrations (range, 35 to 630 mg per deciliter [2 to 35 mmol per liter]), but no ketosis. Tests for antibodies against insulin, glutamic acid decarboxylase, and protein tyrosine phosphatase-like molecule IA-2 (a major target an-tigen of cytoplasmic islet-cell antibodies) were negative. Basal and glucagon-stimulated serum C-peptide concentrations were nearly undetectable on several occasions. Plasma glucagon concentrations were within the normal range. The girl had no digestive problems. When the girl was five years old, epilepsy developed, probably as a sequela of a neonatal brain abscess, and she subsequently had mild learning and behavioral difficulties. Her motor development was normal. At the age of 15 years, the glycemic response to glu-cagon was normal. Her sister (Subject III-6 in Fig. 1) presented with typical type 1 diabetes at the age of seven years. Her mother (Subject II-7 in Fig. 1) was given a diagnosis of gestational diabetes at the age of 25 years. Her father (Subject II-6 in Fig. 1) had impaired fasting glycemia that was treated with diet. Subject 2 An eight-year-old girl of Italian ancestry (Subject III-1 in Family 2 in Fig. 2) had had hyperglycemia (blood glucose, 715 mg per deciliter [40 mmol per liter]) and marked growth retardation when she was born at 38 weeks' gestation (birth weight, 1650 g-less than the 3rd percentile). She had been treated with insulin since birth, initially with a dose of 2 U per kilogram per day and currently with a dose of 1.4 U per kilogram per day. No diabetes-related antibodies (i.e., against insulin or glutamic acid decarboxy-lase) were detected. Basal serum C-peptide concentrations were low at birth, declined further with age, and did not increase in response to glucagon. The girl had no evidence of diabetic complications. Her mother had impaired fasting glycemia, and her father had impaired glucose tolerance. METHODS The studies were approved by the ethics committees of each institution and performed according to the Declaration of Helsinki. Written informed consent was obtained from all subjects or their parents. Molecular Genetic Studies The exons, flanking introns, and promoter regions of the genes encoding hepatocyte nuclear factors 1 a and 4 a , insulin promoter factor 1, the NK-2 (drosophila) homeobox homologue 2, neuro-genic differentiation factor 1-beta-cell E-box transactivator 2, and glucokinase were screened for mutations in members of Family 1 by direct sequencing of polymerase-chain-reaction (PCR) products. The genes for insulin promoter factor 1, NK-2 homeobox homo-logue 6, and glucokinase were screened for mutations in Subject III-1 in Family 2 by single-strand conformation polymorphism analysis (in the case of insulin promoter factor 1) or denaturing gradient gel electrophoresis (in the case of the other two genes) and sequencing of any PCR products with altered mobility. Kinetic Analysis of Recombinant Wild-Type and Mutant Glucokinase Wild-type and mutant forms of human beta-cell glucokinase were expressed in Escherichia coli , and the kinetic properties of the purified proteins in the presence of 2 mmol of dithiothreitol per liter of reaction mixture were determined as described previously. 5 We used nonlinear kinetics according to the Hill equation. The relative-activity index was used as a measure of the glucose phosphoryla-tion capacity of the enzyme. 5 We normalized this relative-activity index to a value of 90 mg of basal glucose per deciliter (5 mmol per liter) with the use of the expression coefficient (5 h ¬2) ÷ (5 h +S 0.5 h), where h is the Hill coefficient (a coefficient that characterizes the sigmoidal glucose dependency of glucokinase) and S 0.5 is the glu-The New England Journal of Medicine is produced by NEJM Group, a division of the Massachusetts Medical Society.