Abstract :
[en] BACKGROUND
Etiological diagnosis of hypoglycaemia in infancy is a complex process, requiring careful integration of detailed history, clinical and laboratory data. The causes of recurrent infant hypoglycaemia include excessive insulin secretion, surreptitious insulin administration, deficiency of counter-regulatory hormones and inborn errors of metabolism.
CLINICAL CASE
A 10 month old girl was admitted at our emergency unit for generalized seizures without fever. Routine laboratory investigations were normal but blood glucose level was at 31 mg/dl. No ketone bodies were found in the urine. Past medical history revealed failure to thrive. A first seizure episode at 8 months of age during family’s holiday is reported. Tests performed in a foreign hospital revealed glycaemia at 36mg/dl. During her stay in our paediatric unit, several hypoglycaemias (31-45 mg/dl) were documented related to irritability as initial symptom of neuroglucopaenia. Detailed medical history revealed that fast tolerance was shorten with hypoglycaemia documented between one to three hours after eating. Clinical examination showed absence of hepatomegaly and failure to thrive: weight, -3SD; height, -2SD, and cranial circumference -2SD. At the time of hypoglycaemia, urinary tests revealed absence of ketonuria, that basically evokes hyperinsulinism or fatty acid oxidation deficiencies but these deficiencies were rapidly excluded by the very short fast state. Blood acylcarnitine profile was normal. Hyperinsulinism is defined by a ratio glycaemia/insulin below 4 with insulin values not necessary high. Since hyperinsulinism can not be excluded with only one blood measure, series of taking were performed during 24 hours. One of these tests was clearly positive with ratio equal to 2.3 (glycaemia at 41 mg/dl, insulin at 18µU/ml).
For this patient, ammonemia was also tested with values ranged from 242 to 275 µg/dl (normal < 125) and the diagnosis of hyperinsulinism/hyperammoniemia (hi/ha) was made and confirmed by molecular analysis (mutation c.965G>A (p.R269H) in the GLUD1 gene).
The treatment consists in this case by diazoxide and reduction of leucine intakes (< 200 mg of leucine/meal).
DISCUSSION
Differential diagnosis of hypoglycaemia with absence of ketonuria and absence of hepatomegaly include fatty acids β-oxidation defects, ketogenesis defects and hyperinsulinisms. Short fasting and post-prandial induced hypoglycaemia pointed to hyperinsulinism in our patient. Congenital hyperinsulinism includes KATP, glucokinase or glutamate deshydrogenase mutations.
Hi/ha syndrome is due to activating mutations in the GLUD1 gene, coding for the glutamate dehydrogenase (GDH). Such mutations reduce the sensitivity of the enzyme to allosteric inhibition by GTP and consequently increase its sensitivity to allosteric activation by L-leucine. Hyperactivity of the GDH is responsible for over-oxidation of glutamate in β-pancreatic cells, increase of the ATP/ADP ratio and insulin release. Hyperactivity of GDH in liver is also responsible for hyperammonemia, which is usually mild and considered harmless for the brain. Nevertheless, recent studies have shown an increased epilepsy risk in cohorts of patients with hi/ha.
CONCLUSION
This case points out the importance of necessity for first investigations of infant documented case of hypoglycaemia. Patient history must focus on symptoms such as shorten fast tolerance periods and neurological symptoms of glucose deprivation. Blood samples should be taken at the time of hypoglycaemia and urine samples as soon as possible after the episode of hypoglycaemia. Initial normal insulin values do not allow the exclusion of the diagnosis of hyperinsulinism.