Paternally inherited ABCC8 mutation causing diffuse congenital hyperinsulinism

Background: Congenital hyperinsulinism (CHI) is a rare genetic disorder characterised by inappropriate insulin secretion in the face of severe hypoglycaemia. There are two histological subtypes of CHI namely diffuse and focal. Diffuse CHI is most common due to recessive mutations in ABCC8/KCNJ11 (which encode the SUR/KIR6.2 components of the pancreatic β-cell K(ATP) channel) whereas focal CHI is due to a paternally inherited ABCC8/KCNJ11 mutation and somatic loss of heterozygosity for the 11p allele inside the focal lesion. Fluorine-18-l-dihydroxyphenylalanine positron emission tomography/computed tomography ((18)F-DOPA-PET/CT) is used in the pre-operative localisation of focal lesions prior to surgery. Diffuse CHI if medically unresponsive will require a near total pancreatectomy whereas focal CHI will only require a limited lesionectomy, thus curing the patient from the hypoglycaemia. Aims: To report the first case of genetically confirmed CHI in Singapore from a heterozygous paternally inherited ABCC8 mutation. Methods/Results: A term male infant presented with severe hyperinsulinaemic hypoglycaemia (HH) after birth and failed medical treatment with diazoxide and octreotide. Genetic testing (paternally inherited mutation in ABCC8/p.D1472N) suggested focal disease, but due to the unavailability of (18)F-DOPA-PET/CT to confirm focal disease, a partial pancreatectomy was performed. Interestingly, histology of the resected pancreatic tissue showed changes typical of diffuse disease. Conclusion: Heterozygous paternally inherited ABCC8/KCNJ11 mutations can lead to diffuse or focal CHI. LEARNING POINTS: HH is a cause of severe hypoglycaemia in the newborn period. Paternal mutations in ABCC8/KCNJ11 can lead to diffuse or focal disease. (18)F-DOPA-PET/CT scan is the current imaging of choice for localising focal lesions. Gallium-68 tetra-aza-cyclododecane-N N′N″N-‴-tetra-acetate octreotate PET scan is not a useful imaging tool for localising focal lesions. The molecular mechanism by which a heterozygous ABCC8 mutation leads to diffuse disease is currently unclear. Focal lesions are curable by lesionectomy and so genetic studies in patients with HH must be followed by imaging using (18)F-DOPA-PET/CT scan.