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Extremes of clinical and enzymatic phenotypes in children with hyperinsulinism caused by glucokinase activating mutations.

Sayed S, Langdon DR, Odili S, Chen P, Buettger C, Schiffman AB, Suchi M, Taub R, Grimsby J, Matschinsky FM, Stanley CA - Diabetes (2009)

Bottom Line: Kinetic analysis of the enzymes included determinations of stability, activity index, the response to glucokinase activator drug, and the effect of glucokinase regulatory protein.Diazoxide treatment was effective in child 3 but ineffective in child 1 and only partially effective in child 2.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.

View Article: PubMed Central - PubMed

Affiliation: Clinical Translational Research Center, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA.

ABSTRACT

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 beta-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.

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Related in: MedlinePlus

Plasma glucose and β-hydroxybutyrate responses to fasting in child 2. Mean plasma glucose was 64 ± 1 mg/dl. β-Hydroxybutyrate values increased from 0.1 to 1.8 mmol/l, whereas fasting plasma glucose levels decreased. At the end of the fast, plasma C-peptide was suppressed (0.16 nmol/l, normal 0.26–1.32 nmol/l). Glucose response to glucagon stimulation was 36 mg/dl. Reference normals when fasting blood glucose <50 mg/dl: β-hydroxybutyrate >2.5 mmol/l, and glycemic response to glucagon >30 mg/dl. △, plasma glucose (SureStep bedside meter); ▲, β-hydroxybutyrate (Precision Xtra bedside meter).
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Figure 2: Plasma glucose and β-hydroxybutyrate responses to fasting in child 2. Mean plasma glucose was 64 ± 1 mg/dl. β-Hydroxybutyrate values increased from 0.1 to 1.8 mmol/l, whereas fasting plasma glucose levels decreased. At the end of the fast, plasma C-peptide was suppressed (0.16 nmol/l, normal 0.26–1.32 nmol/l). Glucose response to glucagon stimulation was 36 mg/dl. Reference normals when fasting blood glucose <50 mg/dl: β-hydroxybutyrate >2.5 mmol/l, and glycemic response to glucagon >30 mg/dl. △, plasma glucose (SureStep bedside meter); ▲, β-hydroxybutyrate (Precision Xtra bedside meter).

Mentions: Figure 1 shows the diurnal profile of plasma glucose levels in child 1 and child 3 (at ages 4 and 15 years, respectively). Glucose values ranged between narrow limits, rarely rising into the normal range even after meals, but also rarely falling very low, even during 12 h of overnight fasting (child 3). Child 1, whose hypoglycemia was more difficult to manage, had significantly lower mean plasma glucose levels (mean ± SE) than child 3 (50 ± 2 vs. 63 ± 1 mg/dl, respectively; P < 0.0001). As shown in Fig. 2, child 2 fasted for 24 h with a stable plasma glucose ranging from 3 to 4 mmol/l (54–72 mg/dl) before dropping to 2.8 mmol/l (50 mg/dl). During the fast he developed a significant ketonemic response, albeit lower than normally seen at this level of blood glucose (β-hydroxybutyrate >2.5 mmol/l).


Extremes of clinical and enzymatic phenotypes in children with hyperinsulinism caused by glucokinase activating mutations.

Sayed S, Langdon DR, Odili S, Chen P, Buettger C, Schiffman AB, Suchi M, Taub R, Grimsby J, Matschinsky FM, Stanley CA - Diabetes (2009)

Plasma glucose and β-hydroxybutyrate responses to fasting in child 2. Mean plasma glucose was 64 ± 1 mg/dl. β-Hydroxybutyrate values increased from 0.1 to 1.8 mmol/l, whereas fasting plasma glucose levels decreased. At the end of the fast, plasma C-peptide was suppressed (0.16 nmol/l, normal 0.26–1.32 nmol/l). Glucose response to glucagon stimulation was 36 mg/dl. Reference normals when fasting blood glucose <50 mg/dl: β-hydroxybutyrate >2.5 mmol/l, and glycemic response to glucagon >30 mg/dl. △, plasma glucose (SureStep bedside meter); ▲, β-hydroxybutyrate (Precision Xtra bedside meter).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2682682&req=5

Figure 2: Plasma glucose and β-hydroxybutyrate responses to fasting in child 2. Mean plasma glucose was 64 ± 1 mg/dl. β-Hydroxybutyrate values increased from 0.1 to 1.8 mmol/l, whereas fasting plasma glucose levels decreased. At the end of the fast, plasma C-peptide was suppressed (0.16 nmol/l, normal 0.26–1.32 nmol/l). Glucose response to glucagon stimulation was 36 mg/dl. Reference normals when fasting blood glucose <50 mg/dl: β-hydroxybutyrate >2.5 mmol/l, and glycemic response to glucagon >30 mg/dl. △, plasma glucose (SureStep bedside meter); ▲, β-hydroxybutyrate (Precision Xtra bedside meter).
Mentions: Figure 1 shows the diurnal profile of plasma glucose levels in child 1 and child 3 (at ages 4 and 15 years, respectively). Glucose values ranged between narrow limits, rarely rising into the normal range even after meals, but also rarely falling very low, even during 12 h of overnight fasting (child 3). Child 1, whose hypoglycemia was more difficult to manage, had significantly lower mean plasma glucose levels (mean ± SE) than child 3 (50 ± 2 vs. 63 ± 1 mg/dl, respectively; P < 0.0001). As shown in Fig. 2, child 2 fasted for 24 h with a stable plasma glucose ranging from 3 to 4 mmol/l (54–72 mg/dl) before dropping to 2.8 mmol/l (50 mg/dl). During the fast he developed a significant ketonemic response, albeit lower than normally seen at this level of blood glucose (β-hydroxybutyrate >2.5 mmol/l).

Bottom Line: Kinetic analysis of the enzymes included determinations of stability, activity index, the response to glucokinase activator drug, and the effect of glucokinase regulatory protein.Diazoxide treatment was effective in child 3 but ineffective in child 1 and only partially effective in child 2.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.

View Article: PubMed Central - PubMed

Affiliation: Clinical Translational Research Center, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA.

ABSTRACT

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 beta-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.

Show MeSH
Related in: MedlinePlus