Endocrine Abstracts (2011) 27 P83

Galactokinase deficiency in a patient with congenital hyperinsulinism: the cautionary tale of using bedside blood glucose monitors

Mashbat Bayarchimeg1,2,3, Dunia Ismail1,2,3, Amanda Lam1,2,3, Derek Burk1,2,3, Jeremy Kirk1,2,3, Wolfgang Hogler1,2,3, Sarah Flanaghan1,2,3, Sian Ellard1,2,3 & Khalid Hussain1,2,3

1Institute of Child Health and Great Ormond Street Hospital, London, UK; 2Department of Endocrinology and Diabetes, Birmingham, UK; 3Institute of Biomedical and Clinical Science, Exeter, UK.

Background: Galactokinase catalyses the first committed step in galactose metabolism, the conversion of galactose to galactose-1-phosphate. Galactokinase deficiency is an extremely rare form of galactosaemia and the most frequent complication reported is cataracts. Congenital hyperinsulinism (CHI) is a cause of severe hypoglycaemia in the newborn period.

Aims: To report the diagnostic pitfalls with bedside blood glucose testing in a neonate with combined galactokinase deficiency and severe congenital hyperinsulinism.

Patients/methods: A term baby girl from consanguineous parents presented with poor feeding, irritability and seizures. Capillary blood glucose testing using bedside test strips and glucometer showed a glucose level of 18 mmol/l but the actual laboratory blood glucose level (measured by glucose oxidase method) was only 1.8 mmol/l. Urine reducing substances were positive. Once oral feeding, the main dietary source of galactose, was stopped the test capillary blood glucose level correlated with the laboratory blood glucose level.

Results: Biochemically the patient had CHI (blood glucose 2.3 mmol/l with simultaneous insulin of 30 mU/l) and galactokinase deficiency (with elevated serum galactose level of 0.62 μmol/h per g Hb). The CHI failed to respond to medical treatment and required a near total pancreatectomy. Homozygous mutations in ABCC8 (E128K (c.382G>A; p.Glu128Lys) in exon 3) gene and GALK1 (homozygous R256W (c.766C>T; p.Arg256Trp) missense mutation in exon 5) lead to CHI and galactokinase deficiency respectively.

Conclusion: This is the first reported case of CHI and galactokinase occurring in the same patient. Severe hypoglycaemia in neonates with CHI may go undetected with bedside blood glucose meters in the presence of galactokinase deficiency.