David R. Langdon

Extremes of Clinical and Enzymatic Phenotypes in Children With Hyperinsulinism Caused by Glucokinase Activating Mutations

OBJECTIVE Heterozygous activating mutations of glucokinase have been reported to cause hypoglycemia attributable to hyperinsulinism in a limited number of families. We report three children with de novo glucokinase hyperinsulinism mutations who displayed a spectrum of clinical phenotypes corresponding to marked differences in enzyme kinetics. RESEARCH DESIGN AND METHODS Mutations were directly sequenced, and mutants were expressed as glutathionyl S-transferase–glucokinase fusion proteins. Kinetic analysis of the enzymes included determinations of stability, activity index, the response to glucokinase activator drug, and the effect of glucokinase regulatory protein. RESULTS Child 1 had an ins454A mutation, child 2 a W99L mutation, and child 3 an M197I mutation. Diazoxide treatment was effective in child 3 but ineffective in child 1 and only partially effective in child 2. Expression of the mutant glucokinase ins454A, W99L, and M197I enzymes revealed a continuum of high relative activity indexes in the three children (26, 8.9, and 3.1, respectively; wild type = 1.0). Allosteric responses to inhibition by glucokinase regulatory protein and activation by the drug RO0281675 were impaired by the ins454A but unaffected by the M197I mutation. Estimated thresholds for glucose-stimulated insulin release were more severely reduced by the ins454A than the M197I mutation and intermediate in the W99L mutation (1.1, 3.5, and 2.2 mmol/l, respectively; wild type = 5.0 mmol/l). CONCLUSIONS These results confirm the potency of glucokinase as the pancreatic β-cell glucose sensor, and they demonstrate that responsiveness to diazoxide varies with genotype in glucokinase hyperinsulinism resulting in hypoglycemia, which can be more difficult to control than previously believed.

Vitamin D Status in Abused and Nonabused Children Younger Than 2 Years Old With Fractures

OBJECTIVE: To examine vitamin D levels in children with (1) suspected abusive and accidental fractures, (2) single and multiple fractures, and (3) fracture types highly associated with inflicted trauma. DESIGN AND METHODS: A study of children younger than 2 years of age with fractures admitted to a large childrens hospital was performed. Bivariate analysis and test for trend were performed to test for the association of vitamin D status and biochemical markers of bone health with the primary outcomes of fracture etiology, number, and type. RESULTS: Of 118 subjects in the study, 8% had deficient vitamin D levels (<20 ng/mL; <50 nmol/L), 31% were insufficient (≥20 < 30 ng/mL; ≥50 < 78 nmol/L), and 61% were sufficient (≥30 ng/mL; ≥78 nmol/L). Lower vitamin D levels were associated with higher incidences of hypocalcemia (P = .002) and elevated alkaline phosphatase (P = .05) but not hypophosphatemia (P = .30). The majority of children sustained accidental fractures (60%); 31% were nonaccidental and 9% were indeterminate. There was no association between vitamin D levels and any of the following outcomes: child abuse diagnosis (P = .32), multiple fractures (P = .24), rib fractures (P = .16), or metaphyseal fractures (P = .49). CONCLUSIONS: Vitamin D insufficiency was common in young children with fractures but was not more common than in previously studied healthy children. Vitamin D insufficiency was not associated with multiple fractures or diagnosis of child abuse. Nonaccidental trauma remains the most common cause of multiple fractures in young children.

Impaired Glycogenic Substrate Activation of Glycogen Synthase Is Associated With Depressed Synthase Phosphatase Activity in Diabetic Rat Liver

Glucose and gluconeogenic substrates promote the activation of hepatic glycogen synthase in vivo and in vitro; activation occurs as inactive glycogen synthase D is dephosphorylated to active glycogen synthase I by glycogen synthase phosphatase. Impairments of glycogen accumulation and glycogen synthase activation in diabetes have been attributed to decreased glycogen synthase phosphatase activity. To determine the role of glycogen synthase phosphatases associated with cytosol and smooth endoplasmic reticulum in the impairment of glycogen synthase activation, livers of normal and streptozotocin-diabetic fed rats were sampled by freeze-clamping before and after perfusion with a mixture of 25 mM glucose, 10 mM glutamine, 4 mM lactate, and 1 mM pyruvate. Perfusion induced activation of glycogen synthase in normal rats, but activation was reduced in the diabetic rats in proportion to the severity of insulin deficiency (r = 0.72, P < 0.0001). There was also a close correlation between insulin levels and glycogen synthase phosphatase activities of both cytosol (r = 0.76, P < 0.0001) and SER (r = 0.71, P < 0.0001) fractions. In contrast, glycogen phosphorylase phosphatase activity and inactivation of glycogen phosphorylase during perfusion were normal in the diabetic livers. This is the first demonstration that glycogen synthase phosphatase activities in both soluble and SER fractions of liver cells are closely related to circulating insulin levels, and that the impairment of glycogen synthesis in diabetes may result from deficient glycogen synthase phosphatase activity in both cell compartments.

The evaluation of peripheral neuropathy in youth with type 1 diabetes

Of 151 youth with type 1 diabetes who were screened for peripheral neuropathy, and received nerve conduction studies, 11% were diagnosed with Diabetic Peripheral Neuropathy (DPN). DPN can occur in young children, with short diabetes duration, and good diabetes control. National guidelines for screening children for DPN should be developed.

Comparison of single- and split-dose insulin regimens with 24-hour monitoring

It has been asserted that twice daily injections of mixed insulin provide better blood glucose control than one. To compare the two regimens we conducted a random-order, double-crossover trial in ten diabetic children. Each regimen lasted for six weeks, concluding with a hospital evaluation. Control at home was assessed by a urine log and determination of glycosylated hemoglobin. Control in the hospital was assessed with measurements of quantitative urinary glucose, serum lipids, and by 24-hour blood sampling for glucose, C-peptide, and counterregulatory hormones. For the group as a whole, none of the indices of control demonstrated a significant advantage for either regimen. Individually, several children did appear to achieve better control on one regimen than the other. Indices of control at home did not consistently predict control in the hospital. In the hospital, the largest increases in glucose concentration followed breakfast (mean rise 148 mg/dl), and standardized exercise invariably reduced plasma glucose values (mean decrement 60 mg/dl). C-Peptide concentrations were low, but higher values were associated with better control. Although a split insulin regimen may improve metabolic control in some patients, this study did not demonstrate a substantial advantage for the majority of subjects over the short period of the trials.

Racial disparities in screening for diabetic retinopathy in youth with type 1 diabetes

Of 1112 children with type 1 diabetes, dilated eye exams were performed in 717 (64%). Children were less likely to be screened for diabetic retinopathy (DR) if they were black (OR=1.6; p=0.005) or had poorer diabetes control (p=0.002). Those at greatest risk for DR were least likely to be screened.

Congenital Hyperinsulinism and Hypopituitarism Attributable to a Novel Mutation in FOXA2

Context Persistent hypoglycemia in the newborn period most commonly occurs as a result of hyperinsulinism. The phenotype of hypoketotic hypoglycemia can also result from pituitary hormone deficiencies, including growth hormone and adrenocorticotropic hormone deficiency. Forkhead box A2 (Foxa2) is a transcription factor shown in mouse models to influence insulin secretion by pancreatic β cells. In addition, Foxa2 is involved in regulation of pituitary development, and deletions of FOXA2 have been linked to panhypopituitarism. Objective To describe an infant with congenital hyperinsulinism and hypopituitarism as a result of a mutation in FOXA2 and to determine the functional impact of the identified mutation. Main Outcome Measure Difference in wild-type (WT) vs mutant Foxa2 transactivation of target genes that are critical for β cell function (ABCC8, KNCJ11, HADH) and pituitary development (GLI2, NKX2-2, SHH). Results Transactivation by mutant Foxa2 of all genes studied was substantially decreased compared with WT. Conclusions We report a mutation in FOXA2 leading to congenital hyperinsulinism and hypopituitarism and provide functional evidence of the molecular mechanism responsible for this phenotype.

Development of a youth-report measure of DPN symptoms: Conceptualization and content validation

Aims To develop a content valid youth-report measure of diabetic peripheral neuropathy (DPN) symptoms. Methods Semi-structured interviews with 5 clinicians and 15 youth aged 8–17 with diabetes were conducted to elicit and clarify youth’s DPN experiences. A systematic review of existing adult-report DPN symptom measures was conducted to identify item concepts representative of each experience. The concepts were transformed into items that were iteratively revised based on cognitive interviews (n = 13 youth aged 8–17) and readability analyses. Results Clinician and youth interviews supported a tripartite conceptual framework of youth DPN symptoms: paresthesia, pain, and anesthesia. Forty-eight youth-report items were generated to represent DPN symptoms identified through the semi-structured interviews and a systematic review of 13 symptom questionnaires for adults. Of these, 23 were eliminated and 3 were revised based on cognitive interviews conducted with youth. The remaining 25 items were on average, written at a 3rd grade reading level. Conclusions This study is the first to generate a content valid self-report measure of youth’s lived experiences with DPN that uses developmentally appropriate terminology. With further psychometric testing, the measure could be used to advance research on pediatric DPN and enhance clinicians’ capacity to identify the condition in childhood.

Diabetic peripheral neuropathy in youth.

Neuropathy is a common long-term complication of diabetes recognized almost entirely in adults (Moser et al., 2013). It is a precursor to foot ulcers and lower limb amputations, both of which are preventable (Fletcher, 2006; Zangaro & Margaret, 1999). The pathogenesis of diabetic peripheral neuropathy (DPN) is not completely understood. Evidence suggests that hyperglycemia and other metabolic factors contribute to nerve damage, at least in part by degrading the function of small blood vessels supplying the nerves, resulting in progressive structural deterioration of nerve pathways (Trotta, Verrotti, Salladini, & Chiarelli, 2004). Hyperglycemia may disrupt myelin nerve sheaths, causing motor nerve conduction slowing and impaired sensory perception. For many years it was believed that DPN was simply a condition that develops after years of diabetes and directly related to the degree of blood sugar control (Glastras, Mohsin, & Donaghue, 2005). However, there is accumulating evidence suggestive of subclinical changes of nerve function shortly after diagnosis even in children. In addition to hyperglycemia, there are other factors that may contribute to an increased risk of symptomatic or asymptomatic neuropathy including taller stature, elevated lipids, smoking, elevated diastolic blood pressure, puberty and autoimmunity (Donaghue & Silink, 1999; Spollett, 2006; Su et al., 2012; Trotta et al., 2004). The clinical effects of this sensory neuropathy include painful burning and tingling sensations that can progress to numbness and eventual loss of protective sensation in the feet. This loss of sensation renders the feet vulnerable to unsuspected trauma, infection, and eventually ulceration (National Diabetes Education Program, 2000). The risk of lower limb amputation increases substantially with repeated