Non-coding cis-regulatory variants in HK1 cause congenital hyperinsulinism with variable disease severity

Background: We recently reported non-coding variants in a cis-regulatory element of the beta-cell disallowed gene hexokinase 1 (HK1) as a novel cause of congenital hyperinsulinism. These variants lead to a loss of repression of HK1 in pancreatic beta-cells, causing insulin secretion during hypoglycaemia. In this study, we aimed to determine the prevalence, genetics, and phenotype of HK1-hyperinsulinism by screening a large international cohort of patients living with the condition. Methods: We screened the HK1 cis-regulatory region in 1761 probands with hyperinsulinism of unknown aetiology who had been referred to one of three large European genomics laboratories. Results: We identified a HK1 variant in 89/1761 probands (5%) and 63 family members. Within the Exeter HI cohort, these variants accounted for 2.8% of all positive genetic diagnoses (n = 54/1913) establishing this as an important cause of HI. Individuals with a disease-causing variant were diagnosed with hyperinsulinism between birth and 26 years (median: 7 days) with variable response to treatment; 80% were medically managed and 20% underwent pancreatic surgery due to poor response to medical therapy. Glycaemic outcomes varied from spontaneous remission to hypoglycaemia persisting into adulthood. Eight probands had inherited the variant from a parent not reported to have hyperinsulinism (median current age: 39 years), confirming variable penetrance. Two of the 23 novel HK1 variants allowed us to extend the minimal cis-regulatory region from 42 to 46 bp. Conclusions: Non-coding variants within the HK1 cis-regulatory region cause hyperinsulinism of variable severity ranging from neonatal-onset, treatment-resistant disease to being asymptomatic into adulthood. Discovering variants in 89 families confirms HK1 as a major cause of hyperinsulinism and highlights the important role of the non-coding genome in human monogenic disease.