Evaluation of fasts for investigating hypoglycaemia or suspected metabolic disease

Idiopathic Pathological Ketotic Hypoglycemia: Finding the Needle in a Haystack

Sick children often have a decreased appetite and experience vomiting and diarrhea; however, hypoglycemia (plasma glucose concentration ≤50 mg/dL or 2.8 mmol/L) is rare. Ketotic hypoglycemia (KH) is the most common cause of hypoglycemia presenting to an Emergency Department in a previously healthy child between 6 months and 6 years of age. Ketosis and hypoglycemia are now well understood to be normal physiologic responses of young children to prolonged fasting.There is now substantial evidence that the term KH describes a variety of conditions including both the lower end of the normal distribution of fasting tolerance in young children as well as numerous rare disorders that impair fasting adaptation. Recent advances in molecular genetic testing have led to the discovery of these rare disorders. Idiopathic pathological KH is a diagnosis of exclusion that describes rare children who have abnormally limited fasting tolerance, experience recurrent episodes of KH, or develop symptoms of hypoglycemia despite elevated ketone levels, and in whom an explanation cannot be found despite extensive investigation. This review provides an approach to distinguishing between physiological KH and pathological KH and includes recommendations for management.

Fasting ketone levels vary by age: implications for differentiating physiologic from pathologic ketotic hypoglycemia

OBJECTIVES

Ketone production is a physiological phenomenon that occurs during beta-oxidation of free fatty acids. Distinguishing physiologic ketosis from pathologic over-production/underutilization of ketones is critical as part of the diagnostic evaluation of disorders of carbohydrate metabolism, but there is limited literature on normal ketone production with fasting. Our aim is to measure fasting serum beta-hydroxybutyrate (BHB) concentrations in healthy children after an overnight fast.

METHODS

Children ≤18 years of age were prospectively recruited from elective procedures through our surgery centers. Exclusion criteria included a history of diabetes, hypopituitarism, adrenal, metabolic or inflammatory disorders, dietary restrictions, trauma, or use of medications that might affect blood glucose. Serum glucose, cortisol, and BHB were assessed after an overnight fast.

RESULTS

Data from 94 participants (mean 8.3 ± 5.7 years, 54 % male, 46 % female, were analyzed. Children ≤3 years of age (19) have significantly higher mean (0.40 ± 0.06 mmol/L) and median (0.4, IQR 0.2-0.6 mmol/L) BHB concentrations compared to children >3 years of age (75) with mean (0.21 ± 0.02 mmol/L) and median BHB (0.1, IQR 0.1-0.2 mmol/L) (p<0.0001). Fasting BHB levels of >1.0 mmol/L was rare (2 %, N=2) and 74 % (N=70) of participants had BHB levels <0.3 mmol/L.

CONCLUSIONS

BHB concentrations are significantly higher in young children (≤3 years of age) compared to older children. Fasting BHB levels >1.0 mmol/L are rare within our population and therefore may identify a value above which there may a greater concern for pathologic ketotic hypoglycemia. It is imperative to establish the normative range in children to differentiate physiological from pathological ketotic hypoglycemia.

Dynamic Methods for Childhood Hypoglycemia Phenotyping: A Narrative Review

Hypoglycemia results from an imbalance between glucose entering the blood compartment and glucose demand, caused by a defect in the mechanisms regulating postprandial glucose homeostasis. Hypoglycemia represents one of the most common metabolic emergencies in childhood, potentially leading to serious neurologic sequelae, including death. Therefore, appropriate investigation of its specific etiology is paramount to provide adequate diagnosis, specific therapy and prevent its recurrence. In the absence of critical samples for biochemical studies, etiological assessment of children with hypoglycemia may include dynamic methods, such as in vivo functional tests, and continuous glucose monitoring. By providing detailed information on actual glucose fluxes in vivo, proof-of-concept studies have illustrated the potential (clinical) application of dynamic stable isotope techniques to define biochemical and clinical phenotypes of inherited metabolic diseases associated with hypoglycemia. According to the textbooks, individuals with glycogen storage disease type I (GSD I) display the most severe hypoglycemia/fasting intolerance. In this review, three dynamic methods are discussed which may be considered during both diagnostic work-up and monitoring of children with hypoglycemia: 1) functional in vivo tests; 2) in vivo metabolic profiling by continuous glucose monitoring (CGM); 3) stable isotope techniques. Future applications and benefits of dynamic methods in children with hypoglycemia are also discussed.

Investigating paediatric hypoglycaemia: Dynamic studies at a tertiary paediatric hospital

AIM

Paediatric hypoglycaemia often requires specific investigations to determine aetiology. Samples from the time of hypoglycaemia may not be available and a diagnostic fasting test may be required. Additionally, fasting studies can determine safe fasting intervals and prolonged oral glucose challenges can assess hypoglycaemia due to abnormal post-prandial glucose handling. This audit reviewed the current utility and yield of fasting studies, prolonged oral glucose challenges and starch loads.

METHODS

Retrospective audit of clinical record to determine purpose and outcome of tests performed at a Tertiary Paediatric Endocrine/Metabolic Testing Unit in Sydney, Australia, from 2013 to 2018 inclusive.

RESULTS

One hundred and thirty-eight children (aged 3 weeks-17 years) underwent 170 tests: 122 fasting studies, 20 five-hour OGTTs, 22 uncooked corn starch loads and six modified waxy maize starch (Glycosade) loads. The majority were for diagnostic purposes (n = 113, 66%), with 57 (34%) to guide management in patients with known diagnoses. Following diagnostic studies, 35 (31%) patients received a pathological diagnosis, the most common of which (n = 19, 17%) was accelerated starvation. Hypoglycaemia developed in n = 15/113 (13%) during the diagnostic studies. Management studies helped determine length of safe fast, adjustment of medication or diet and document resolution of pathology.

CONCLUSION

Fasting studies remain a safe and effective method to assist with diagnoses, confirm or exclude pathological causes of childhood hypoglycaemia and to guide management of known diagnoses in the paediatric population.

Hypoketotic hypoglycemia in citrin deficiency: a case report

Background

Citrin deficiency (CD) is a recessive metabolic disease caused by biallelic pathogenic variants in SLC25A13. Although previous studies have reported ketosis in CD, it was observed at the time of euglycemia or mild hypoglycemia. Blood ketone levels concomitant with symptomatic or severe hypoglycemia in CD have not been a topic of focus despite its importance in identifying the etiology of hypoglycemia and assessing the ability of fatty acid utilization. Herein, we describe a patient with CD who had repeated episodes of hypoglycemia with insufficient ketosis.

Case presentation

A 1-year-old boy with repetitive hypoglycemia was referred to us to investigate its etiology. The fasting load for 13 h led to hypoketotic hypoglycemia, indicating the possibility of partial β-oxidation dysfunction. A genetic test led to the diagnosis of CD. The hypoglycemic episodes disappeared after switching to a medium-chain triglyceride-containing formula.

Conclusions

This case report suggests that symptomatic or severe hypoglycemia in patients with CD could be associated with relatively low levels of ketone bodies, implying that β-oxidation in these patients might possibly be partially disrupted. When encountering a patient with hypoglycemia, clinicians should check blood ketone levels and bear in mind the possibility of CD because excessive intravenous administration of glucose can cause decompensated symptoms in patients with CD as opposed to other disorders presenting with hypoketotic hypoglycemia, such as fatty acid oxidation disorders. Further studies in a large-scale cohort are warranted to confirm our speculation.

How to use a controlled fast to investigate hypoglycaemia

Controlled fasts can play a valuable role in the diagnosis and management of hypoglycaemia in paediatric clinical practice, but are no substitute for the collecting of appropriate critical samples at the time of hypoglycaemia for metabolic and endocrine studies. Fatty acid oxidation defects, hyperinsulinism and adrenal insufficiency should always be excluded prior to organising controlled fasts. Controlled fasts are safe if conducted in an experienced setting with strict protocols in place. Failure to adhere to protocol can defeat the purpose of the study and can potentially be dangerous. Proper planning in conjunction with the laboratory and close supervision by staff experienced in controlled fasts is crucial to ensure the best quality information is yielded from these procedures.

Recognition, assessment and management of hypoglycaemia in childhood

Hypoglycaemia is frequent in children and prompt management is required to prevent brain injury. In this article we will consider hypoglycaemia in children after the neonatal period. The most common causes are diabetes mellitus and idiopathic ketotic hypoglycaemia (IKH) but a number of endocrine disorders and inborn errors of metabolism (IEMs) need to be excluded. Elucidation of the diagnosis relies primarily on investigations during a hypoglycaemic episode but may also involve biochemical tests between episodes, dynamic endocrine tests and molecular genetics. Specific treatment such as cortisol replacement and pancreatic surgery may be required for endocrine causes of hypoglycaemia, such as adrenal insufficiency and congenital hyperinsulinism. In contrast, in IKH and most IEMs, hypoglycaemia is prevented by limiting the duration of fasting and maintaining a high glucose intake during illnesses.

Shwachman-Diamond syndrome presenting with early ichthyosis, associated dermal and epidermal intracellular lipid droplets, hypoglycemia, and later distinctive clinical SDS phenotype

Shwachman-Diamond syndrome (SDS) is a recessive ribosomopathy, characterized by bone marrow failure and exocrine pancreatic insufficiency (ePI) often associated with neurodevelopmental and skeletal abnormalities. The aim of this report is to describe a SDS patient with early ichthyosis associated with dermal and epidermal intracellular lipid droplets (iLDs), hypoglycemia and later a distinctive clinical SDS phenotype. At 3 months of age, she had ichthyosis, growth retardation, and failure to thrive. She had not cytopenia. Ultrasonography (US) showed pancreatic diffuse high echogenicity. Subsequently fasting hypoketotic hypoglycemia occurred without permanent hepatomegaly or hyperlipidemia. Continuous gavage feeding was followed by clinical improvement including ichthyosis and hypoglycemia. After 14 months of age, she developed persistent neutropenia and ePI consistent with SDS. The ichthyotic skin biopsy, performed at 5 months of age, disclosed iLDs in all epidermal layers, in melanocytes, eccrine sweat glands, Schwann cells and dermal fibroblasts. These iLDs were reminiscent of those described in Dorfman-Chanarin syndrome (DCS) or Wolman's disease. Both LIPA and CGI-58 analysis did not revealed pathogenic mutation. By sequencing SBDS, a compound heterozygous for a previously reported gene mutation (c.258 + 2T>C) and a novel mutation (c.284T>G) were found. Defective SBDS may hypothetically interfere as in DCS, with neutral lipid metabolism and play a role in the SDS phenotype such as ichthyosis with dermal and epidermal iLDs and hypoglycemia. This interference with neutral lipid metabolism must most likely occur in the cytoplasm compartment as in DCS and not in the lysosomal compartment as in Wolman's disease. © 2016 Wiley Periodicals, Inc.

Elevations of C14:1 and C14:2 Plasma Acylcarnitines in Fasted Children: A Diagnostic Dilemma

OBJECTIVES

To test whether follow-up testing for very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency uncovers a diagnosis in patients with elevations of C14:1 and C14:2 plasma acylcarnitines after a controlled fasting study performed for clinically suspected hypoglycemia and to compare the acylcarnitine profiles from fasted patients without VLCAD deficiency vs patients with known VLCAD deficiency to determine whether metabolite testing distinguishes these groups.

STUDY DESIGN

We performed a retrospective chart review and identified 17 patients with elevated C14:1 and C14:2 plasma acylcarnitine levels after a controlled fast and with testing for VLCAD deficiency (ACADVL sequencing or fibroblast fatty acid oxidation studies). The follow-up testing in all patients was inconsistent with a diagnosis of VLCAD deficiency. We compared the plasma acylcarnitine profiles from these fasted patients vs patients with VLCAD deficiency.

RESULTS

C14:1/C12:1 was significantly lower (P < .001) in fasted patients vs patients with VLCAD deficiency. Metabolomics analysis performed in 2 fasted patients and 1 patient with VLCAD deficiency demonstrated evidence for up-regulated lipolysis and β-oxidation in the fasted state.

CONCLUSIONS

Elevations of plasma C14:1 and C14:2 acylcarnitines appear to be a physiologic result of lipolysis that occurs with fasting. Both metabolomics analysis and/or C14:1/C12:1 may distinguish C14:1 elevations from physiologic fasting-induced lipolysis vs VLCAD deficiency.

Adding Glucagon-Stimulated GH Testing to the Diagnostic Fast Increases the Detection of GH-Sufficient Children

BACKGROUND/AIMS

The evaluation of children with unexplained hypoglycemia may include a diagnostic fast. However, low growth hormone (GH) concentration during hypoglycemia is not specific to GH deficiency (GHD). The aim of this study was to determine if serial GH measurement following glucagon administration, in the setting of a diagnostic fast, would increase the number of children identified as not having GHD.

METHODS

We conducted a retrospective chart review of children who had serial GH measurements performed after glucagon administration at the end of a diagnostic fast. Glucagon was administered at the end of the fasting study, and GH was measured every 30 min for 210 min.

RESULTS

Of the 29 children in this series, only 3 (10%) had GH concentrations >7 ng/ml at the end of the fast, which increased by 16 (55%) after serial GH testing. The percentages of samples with GH concentrations >7 ng/ml were: 10% at baseline, and 25, 39, 41, 41, 33, 43, and 0% every 30 min thereafter.

CONCLUSION

Additional GH measurements after glucagon administration following a diagnostic fast can improve the identification of children without GHD and thereby save them unnecessary GH stimulation testing and potential GH treatment.

Pediatric hypoglycemia

Hypoglycemia in the pediatric population is a common finding important to recognize and manage to prevent brain injury. Recent advances in molecular genetics have provided new insight into its biochemical and physiologic basis and have led to more appropriate and specific treatment. Although a major cause of brain injury in pediatrics, the ability to predict the long-term outcome in these patients remains difficult. Identification of these at-risk individuals is important. The physiologic adaptations associated with transition from fetal to neonatal life are now better understood thus allowing for improved surveillance and management. Despite these advances, analytical limitations of point-of-care testing instruments at low glucose concentration continue to persist, This review aims to address these questions and provide an overview of pediatric hypoglycemia and the molecular pathways involved.

An Evaluation of Growth Hormone and IGF-1 Responses in Neonates with Hyperinsulinaemic Hypoglycaemia

Background. Hyperinsulinaemic Hypoglycaemia (HH) is the most common cause of severe and persistent hypoglycemia in the neonatal period. It has been shown that the neonates with HH fail to generate adequate serum cortisol counterregulatory response to symptomatic hypoglycemia. However the role played by growth hormone (GH) and Insulin-like Growth Factor 1 (IGF-1) is not clear. Objectives. To compare the serum GH, IGF-1, and IGFBP3 responses to HH in neonates undergoing diagnostic fasting studies. Population and Methods. Data was retrospectively collected on full-term neonates who presented with severe and persistent hypoglycemia and were confirmed to have HH. Neonates born with intrauterine growth retardation or those on medical therapy (diazoxide or octreotide) were excluded. Results. 31 neonates with HH (mean gestational age: 38 weeks and mean birth weight: 3.9 kg) were included in the study. The mean age at the time of diagnostic fast was 4 weeks, the mean glucose concentration during the fast was 2.2 mmol/L (SEM ± 0.09), and the mean insulin level was 11.9 mU/L (±2.12). The mean serum GH concentration during the hypoglycaemia was 12.5 µg/L (±1.53). The mean serum IGF-1 and Insulin-like Growth Factor Binding Protein 3 (IGFBP3) levels were 29.2 ng/ml (±7.8) and 1.21 mg/L (±0.13), respectively. The mean cortisol concentration was 201 nmol/L (±33). Conclusions. Whilst the serum IGF-1 and IGFBP3 levels are relatively low during hypoglycaemia, the serum GH level does reflect an appropriate counterregulatory response to HH. The serum cortisol counterregulatory hormonal responses are blunted. Further studies are required to understand the mechanism(s) of these hormonal alterations in neonates with HH.

Dietary dilemmas in the management of glycogen storage disease type I

Over the last 50 years, understanding the biochemical bases of glycogen storage disease type I has led to vastly improved survival and health outcomes but the management still centres around an extremely intensive dietary regimen. Patients' metabolic profiles are really determined by the whole of the diet and it can be very difficult to adjust therapy accordingly. In an iso-energetic diet with reference total energy intake, high carbohydrate intake could compromise other macro- and micro-nutrients; if carbohydrates are not restricted then total energy intake is excessive. The quality of the macronutrient such as the glycemic index of carbohydrate, the type of sugar and the proportion of medium-chain triglyceride and essential fatty acids also has a bearing on an individual's long-term metabolic control with potential clinical correlates. These factors as well as the different requirements between individuals and within individuals as they get older mean that the management of glycogen storage disease type I is particularly fraught. Regular clinical and dietary review is imperative as patients grow, ensuring adequate but not excessive low glycaemic index carbohydrate intake, appropriate dynamic biochemical profiles and suitable age appropriate eating patterns. Without diligent management, and education that empowers the patient, these individuals can struggle in adult life.

Update on investigating hypoglycaemia in childhood

Identification and investigation of hypoglycaemia in childhood remains an important clinical emergency. Rapid recognition and appropriate management of this clinical state continues to be important in order to prevent neurological damage or even death. The purpose of this review is to provide an update on the advances made in this area since the review by Bonham in this journal in 1993. Advances in molecular science and diagnostic techniques have assisted in understanding the mechanisms involved in the homeostasis of glucose metabolism at rest and when stressed. New disorders causing hypoglycaemia are described using the classification based upon aetiologies, which was used in Bonham's original paper. The development and use of guidelines and pre-assembled packs for investigating hypoglycaemia is also discussed.

Metabolic profiles in children during fasting

BACKGROUND

Hypoglycemia is one of the most common metabolic derangements in childhood. To establish the cause of hypoglycemia, fasting tolerance tests can be used. Currently available reference values for fasting tolerance tests have limitations in their use in daily practice.

OBJECTIVE

The aim of this study was to determine the reference values of metabolites involved in glucose homeostasis during fasting in healthy children.

METHODS

This study included a retrospective analysis of 488 fasting tests. All tests of patients (n = 321) with disorders, including metabolic and endocrine disorders, were excluded, as were tests performed in children who were over- or underweight.

RESULTS

In 167 fasting tests performed in the study, hypoglycemia was reached in 52 (31%) tests. On the basis of the time until hypoglycemia was reached, 3 age groups could be defined: (1) children aged 0 to 24 months (median 15 months) (n = 49); (2) children aged 25 to 84 months (median 45 months) (n = 79); (3) and children aged 85 to 216 months (median 106 months) (n = 39). In all groups, a significant increase in ketone body levels and a significant decrease in glucose levels in plasma were observed during fasting. Younger children had a faster increase in ketone body levels and a faster decrease in glucose levels in plasma than older children.

CONCLUSIONS

Reference values of the metabolites involved in glucose homeostasis during fasting in children were generated. Those values can be used to determine whether a child has a normal fasting response. For high-risk children, guidelines concerning maximum fasting time and dietary intervention during illness are of the utmost importance.

[Childhood hypoglycemia: results of prospective evaluation protocols in children with up to 1 year of age]

The aim of this study is to present the experience of applying hypoglycemia evaluation protocol. We performed a prospective study with 13 children with hypoglycemia symptoms at the Hospital of Clinicas of Porto Alegre, with range age 5.3+/-4.5 months and eight patients are female. The patients had been submitted to glucagon fasting test and blood glucose, lactate, pH, C peptide, insulin, fatty acids, TSH, GH, cortisol, and urine ketones were measured. Eight patients presented persistent hypoglycemia and five presented transitory hypoglycemia. The most frequent diagnosis was persistent hyperinsulinism. We suggest the use of a simple protocol for the evaluation of hypoglycemia, which contemplates the identifications of the main etiologies in children and facilitates the handling of these patients.

From hyperinsulinaemic hypoglycaemia to ketotic hypoglycaemia: the range of glucose abnormalities in patients born with intrauterine growth retardation

INTRODUCTION

Newborns with intrauterine growth retardation (IUGR) have multiple risk factors for developing hypoglycaemia. Hyperinsulinism, both transient and prolonged, is one of the major risk factors responsible for the hypoglycaemia observed in some newborns with IUGR. Once the child has progressed beyond the infancy period, the most common cause of hypoglycaemia is ketotic hypoglycaemia. We report our observations of ketotic hypoglycaemia in six children who were born with IUGR and developed hyperinsulinaemic hypoglycaemia (HH) that required treatment with diazoxide and chlorothiazide.

RESULTS

In one of these children the ketotic hypoglycaemia was found to be due to growth hormone deficiency; in the remaining five patients, however, no cause for the hypoglycaemia could be found, despite extensive investigations. These observations suggest that ketotic hypoglycaemia may be more common in children with a history of IUGR. Further studies are required to understand why some newborns with IUGR and HH have an increased risk of ketotic hypoglycaemia in childhood.

CONCLUSION

Newborns with a history of IUGR and HH have an increased risk of developing ketotic hypoglycaemia in the childhood period.

Evaluation of diagnostic fasting in the investigation of hypoglycemia in children omani experienc

OBJECTIVES

To assess the safety and importance of diagnostic fast in the evaluation of hypoglycemia in children in a non-specialist set up.

METHOD

The medical records of 116 patients with hypoglycemia, admitted to Pediatric Unit, Royal Hospital, Muscat, Sultanate of Oman, over a 15 year period, were reviewed. Of these, 96 (82.8%) patients, 52 boys and 44 girls, aged 8 days to 10 years were subjected to diagnostic fast.

RESULTS

Of these 96 patients fasted, 77 (80.2%) became hypoglycemic (HG group) and 19 (19.8 %) did not develop hypoglycemia on fast (NHG group). In the HG group, 69 (89.6%) patients developed symptomatic hypoglycemia of variable severity and none developed coma or convulsions during fasting.

CONCLUSION

The study has proved that diagnostic fast is relatively a safe procedure with considerable amount of diagnostic yield.

Glucose and leucine kinetics in idiopathic ketotic hypoglycaemia

AIMS

To investigate glucose and leucine kinetics in association with metabolic and endocrine investigations in children with ketotic hypoglycaemia (KH) in order to elucidate the underlying pathophysiology.

METHODS

Prospective interventional study using stable isotope tracer in nine children (mean age 4.23 years, range 0.9-9.8 years; seven males) with KH and 11 controls (mean age 4.57 years, range 0.16-12.3 years; four males).

RESULTS

Plasma insulin levels were significantly lower in KH compared to subjects in the non-KH group. Plasma ketone body levels were significantly higher in KH than in non-KH. Basal metabolic rate was significantly higher in subjects with KH (45.48+/-7.41 v 31.81+/-6.72 kcal/kg/day) but the respiratory quotients were similar in both groups (KH v non-KH, 0.84+/-0.05 v 0.8+/-0.04. Leucine oxidation rates were significantly lower in children with KH (12.25+/-6.25 v 31.96+/-8.59 micromol/kg/h). Hepatic glucose production rates were also significantly lower in KH (3.84+/-0.46 v 6.6+/-0.59 mg/kg/min).

CONCLUSIONS

KH is caused by a failure to sustain hepatic glucose production rather than by increased glucose oxidation rates. Energy demand is significantly increased, whereas leucine oxidation is reduced.

Hypoglycaemia and Russell-Silver syndrome

AIM

To determine both the incidence and aetiology of chronic hypoglycaemia in symptomatic children with Russell-Silver syndrome (RSS) during the first four years of life.

STUDY DESIGN

Twenty-four children with RSS under the age of 4 years, who had either clinical symptoms of hypoglycaemia or previous evidence of biochemically documented hypoglycaemia, were admitted to hospital for 48 hours to perform a 24-h cortisol/glucose profile and a diagnostic fast in those who did not develop spontaneous hypoglycaemia. A dietary assessment was also performed. Glucose profile was assessed in 20 children and cortisol profile in 16; combined glucose and cortisol profile in 15 children. Eight children had a diagnostic fast. Mean chronological age at time of assessment was 2.2 +/- 0.8 years (range 1.1-3.9 years).

RESULTS

Ten of 24 children had previously been documented as having hypoglycaemia. Seven of 12 patients were growth hormone (GH) insufficient after a glucagon test. Their feeding pattern was described as 'poor and picky eaters' in all, seven requiring nasogastric tube feeding. The mean spontaneous energy intake (n = 8) was 56 +/- 19.6 kcal/kg/day (range 38-90). Nocturnal sweating was the commonest symptom (23.96%), followed by irritability (11.46%), tantrums (7.29%), pallor and shakiness (3.13%). The glucose profile in seven children showed hypoglycaemia but only four were symptomatic. None of the children was cortisol deficient. The mean period of fasting was 11.8 +/- 4 hours (range 3-18 h). No metabolic/hormonal abnormality, with the exception of GH insufficiency, was detected at the time of hypoglycaemia.

CONCLUSION

Children with RSS are prone to develop spontaneous hypoglycaemia especially if they are not fed both frequently and regularly. The most likely explanation is accelerated starvation and/or GH insufficiency. We suggest guidelines to minimise hypoglycaemia in these children.

Cortisol and growth hormone responses to spontaneous hypoglycaemia in infants and children

AIMS

To evaluate responses of cortisol and growth hormone (GH) to spontaneous hypoglycaemia in infants and children.

METHODS

Retrospective review of laboratory and clinical data in paediatric patients investigated for suspected hypoglycaemia over a five year period. Thirty patients (16 aged <3 months) had hypoglycaemia confirmed by laboratory analysis (glucose <2.5 mmol/l) and were compared with 26 patients (11 aged <3 months) with glucose > or =2.5 mmol/l.

RESULTS

The commonest causes of hypoglycaemia were transient hyperinsulinism in infants <3 months and intercurrent infection in those >6 months of age. In both hypo- and non-hypoglycaemic patients, cortisol was positively (r(s) +0.66 and +0.68) and GH inversely (r(s) -0.65 and -0.75) correlated with age. Hypo- and non-hypoglycaemic infants <3 months had median cortisol concentrations of 205 and 116 nmol/l respectively compared with 1370 and 736 nmol/l in hypo- and non-hypoglycaemic children >6 months. Conversely, median GH was 46.5 and 51.2 mU/l in hypo- and non-hypoglycaemic infants compared with 14.3 and 12.1 mU/l in older hypo- and non-hypoglycaemic patients. Older non-hypoglycaemic patients with glucose levels below the glycaemic thresholds established for cortisol and GH secretion in adults had higher cortisol and GH concentrations than patients whose glucose levels exceeded these thresholds.

CONCLUSIONS

Cortisol and GH responses to spontaneous hypoglycaemia in children are highly age dependent. Young infants mount a poor cortisol response compared with older infants and children. Children older than 6 months may have glycaemic thresholds for cortisol and GH similar to those established for adults.

Surgery of persistent hyperinsulinaemic hypoglycaemia

Hyperinsulinism (HI) is the commonest cause of persistent or recurrent hypoglycaemia in childhood. HI is genetically and phenotypically diverse. Key management issues involve early diagnosis by insuring that appropriate investigations are undertaken at the point of hypoglycaemia, prevention of recurrent hypoglycaemia and clinical, biochemical and genetic characterisation of the HI syndrome. Children with persistent diazoxide resistant HI require investigation at specialist centres to differentiate those with a generalised disorder of the pancreas (diffuse HI; di-HI) from those with localised abnormalities within the pancreas (focal HI; fo-HI). Fo-HI may be managed by selective pancreatic resection of the focal abnormality. Di-HI is only managed by surgery if combination drug therapies are unable to prevent hypoglycaemia. Pancreatic beta-cell dysfunction persists following subtotal pancreatectomy of di-HI.

What is the role of medium-chain triglycerides in the management of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency?

Cardiomyopathy is common in infants with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency. Resolution of the cardiomyopathy can often be achieved by avoidance of fasting and changing from a conventional infant formula to one in which most long-chain fat is replaced by medium-chain triglycerides (MCT). It is uncertain whether the clinical improvement is due to the restriction of long-chain fat or whether the MCT have specific beneficial effects. To clarify this, the metabolic effects of MCT were examined in 5 patients. When given at around the level found in MCT-based infant formula, MCT had no effect on blood concentrations of ketone bodies, specific fatty acids or acylcarnitines. The present study cannot, however, exclude the possibility that MCT per se may have beneficial effects.

Hyperinsulinism in short-chain L-3-hydroxyacyl-CoA dehydrogenase deficiency reveals the importance of beta-oxidation in insulin secretion

A female infant of nonconsanguineous Indian parents presented at 4 months with a hypoglycemic convulsion. Further episodes of hypoketotic hypoglycemia were associated with inappropriately elevated plasma insulin concentrations. However, unlike other children with hyperinsulinism, this patient had a persistently elevated blood spot hydroxybutyrylcarnitine concentration when fed, as well as when fasted. Measurement of the activity of L-3-hydroxyacyl-CoA dehydrogenase in cultured skin fibroblasts with acetoacetyl-CoA substrate showed reduced activity. In fibroblast mitochondria, the activity was less than 5% that of controls. Sequencing of the short-chain L-3-hydroxyacyl-CoA dehydrogenase (SCHAD) genomic DNA from the fibroblasts showed a homozygous mutation (C773T) changing proline to leucine at amino acid 258. Analysis of blood from the parents showed they were heterozygous for this mutation. Western blot studies showed undetectable levels of immunoreactive SCHAD protein in the child's fibroblasts. Expression studies showed that the P258L enzyme had no catalytic activity. We conclude that C773T is a disease-causing SCHAD mutation. This is the first defect in fatty acid beta-oxidation that has been associated with hyperinsulinism and raises interesting questions about the ways in which changes in fatty acid and ketone body metabolism modulate insulin secretion by the beta cell. The patient's hyperinsulinism was easily controlled with diazoxide and chlorothiazide.

Practical management of hyperinsulinism in infancy

Hyperinsulinism in infancy is one of the most difficult problems to manage in contemporary paediatric endocrinology. Although the diagnosis can usually be achieved without difficulty, it presents the paediatrician with formidable day to day management problems. Despite recent advances in understanding the pathophysiology of hyperinsulinism, the neurological outcome remains poor, and there is often a choice of unsatisfactory treatments, with life long sequelae for the child and his or her family. This paper presents a state of the art overview on management derived from a consensus workshop held by the European network for research into hyperinsulinism (ENRHI). The consensus is presented as an educational aid for paediatricians and children's nurses. It offers a practical guide to management based on the most up to date knowledge. It presents a proposed management cascade and focuses on the clinical recognition of the disease, the immediate steps that should be taken to stabilise the infant during diagnostic investigations, and the principles of definitive treatment.

Insulin induced hypoglycaemia: comparison of glucose and glycerol concentrations in plasma and microdialysate from subcutaneous adipose tissue

AIMS

To investigate the dynamics between plasma and dialysate glucose during hypoglycaemia in children.

STUDY DESIGN

Six children in prepuberty or early puberty were investigated by multiple blood sampling and microdialysis of subcutaneous adipose tissue during a standard arginine-insulin tolerance test. Glucose and glycerol, as an index of lipolysis, were measured in samples from both compartments. Plasma concentrations of insulin and the main counterregulatory hormones were also measured.

RESULTS

Plasma and dialysate glucose concentrations were very similar at baseline and increased in concert after infusion of arginine, probably in response to glucagon release. After insulin injection, glucose in both plasma and dialysate fell in parallel. The subsequent hypoglycaemic stress response induced a rapid rebound in the plasma concentration with a mean (SD) delay in the dialysate of 16 (3) minutes. Plasma glycerol was approximately fivefold lower than in the dialysate and did not fluctuate significantly. Dialysate glycerol decreased with arginine infusion and reached a nadir immediately following insulin administration. Subsequently, the antilipolytic effect of insulin was overcome by the hypoglycaemic stress response, and lipolysis prevailed in spite of hyperinsulinaemia.

CONCLUSION

After rapidly induced hypoglycaemia, rebound of interstitial glucose concentrations is significantly delayed compared with plasma concentrations, and the antilipolytic effect of hyperinsulinaemia is opposed possibly by the hypoglycaemic stress response.

Hepatic mitochondrial 3-hydroxy-3-methylglutaryl-coenzyme a synthase deficiency

There are at least two isoenzymes of 3-hydroxy-3-methylglutaryl (HMG)-CoA synthase (EC 4.1.3.5) located in the mitochondrial matrix and the cytoplasm of hepatocytes, respectively. The mitochondrial enzyme is necessary for the synthesis of ketone bodies, which are important fuels during fasting. We report a child with a deficiency of this isoenzyme. He presented at 16 mo with hypoglycemia. There was no rise in ketone bodies during fasting or after a long chain fat load but there was a small rise after a leucine load. Measurement of beta-oxidation flux in fibroblasts was normal. Using antibodies specific for mitochondrial HMG-CoA synthase, no immunoreactive material could be detected on Western blotting. Total HMG-CoA synthase activity in liver homogenate was only slightly lower than in control samples. Presumably, as there was no mitochondrial HMG-CoA synthase enzyme protein, this activity arose from the cytoplasmic or other (e.g. peroxisomal) isoenzymes. With avoidance of fasting, our patient has had no problems since presentation and is developing normally at 4 y of age.

Screening for medium chain acyl-CoA dehydrogenase deficiency using electrospray ionisation tandem mass spectrometry

OBJECTIVE

To establish criteria for the diagnosis of medium chain acyl-CoA dehydrogenase (MCAD) deficiency in the UK population using a method in which carnitine species eluted from blood spots are butylated and analysed by electrospray ionisation tandem mass spectrometry (ESI-MS/MS).

DESIGN

Four groups were studied: (1) 35 children, aged 4 days to 16.2 years, with proven MCAD deficiency (mostly homozygous for the A985G mutation, none receiving carnitine supplements); (2) 2168 control children; (3) 482 neonates; and (4) 15 MCAD heterozygotes.

RESULTS

All patients with MCAD deficiency had an octanoylcarnitine concentration ([C8-Cn]) > 0.38 microM and no accumulation of carnitine species > C10 or < C6. Among the patients with MCAD deficiency, the [C8-Cn] was significantly lower in children > 10 weeks old and in children with carnitine depletion (free carnitine < 20 microM). Neonatal blood spots from patients with MCAD deficiency had a [C8-Cn] > 1.5 microM, whereas in heterozygotes and other normal neonates the [C8-Cn] was < 1.0 microM. In contrast, the blood spot [C8-Cn] in eight of 27 patients with MCAD deficiency > 10 weeks old fell within the same range as five of 15 MCAD heterozygotes (0.38-1.0 microM). However, the free carnitine concentrations were reduced (< 20 microM) in the patients with MCAD deficiency but normal in the heterozygotes.

CONCLUSIONS

Criteria for the diagnosis of MCAD deficiency using ESI-MS/MS must take account of age and carnitine depletion. If screening is undertaken at 7-10 days, the number of false positive and negative results should be negligible. Because there have been no instances of death or neurological damage following diagnosis of MCAD deficiency in our patient group, a strong case can be made for neonatal screening for MCAD deficiency in the UK.

Loss of functional KATP channels in pancreatic beta-cells causes persistent hyperinsulinemic hypoglycemia of infancy

Persistent hyperinsulinemic hypoglycemia of infancy (PHHI) is a disorder of childhood associated with inappropriate hypersecretion of insulin by the pancreas. The pathogenesis of the condition has hitherto remained controversial. We show here that insulin-secreting cells from a homogeneous group of five infants with PHHI lack ATP-sensitive K+ channel (KATP) activity. As a consequence, PHHI beta-cells are spontaneously electrically active with high basal cytosolic Ca2+ concentrations due to Ca2+ influx. Our findings define the pathogenesis of this disease as a novel K+ channel disorder.