Heterozygous variants in the promoter region of the SLC16A1 gene, which encodes the MCT1 protein, cause HI. As of Spring 2025, we are aware of altogether 15 families, with a total of around 50 family members, who have been diagnosed with this condition. However, we believe that SLC16A1-HI is likely to be underdiagnosed, and we are actively working to raise awareness of this condition worldwide. Most of the families we have identified are currently living in Ireland or Finland. Within our cohort of patients with SLC16A1 pathogenic variants, the average age at diagnosis of HI is 21 years, with a range from birth to 41 years. Here is a short video describing our recent findings.
SLC16A1-HI appears to have multiple triggers for hypoglycaemia. Initially, hypoglycaemia following exercise was considered the most notable feature. However, we now understand that many individuals with SLC16A1-HI can also experience hypoglycaemia in other situations. Some people have hypoglycaemia triggered by several different factors, while others may be affected by just one specific trigger. These include, exercise, fasting, high-carbohydrate meals, illness, emotional stress and pregnancy.
Our SLC16A1-HI patient information sheet provides more information on this form of hyperinsulinism. This can be downloaded from our Resources for Families page.
Key References to the Medical Literature
Otonkoski T, Jiao H, Kaminen-Ahola N, Tapia-Paez I, Ullah MS, Parton LE, Schuit F, Quintens R, Sipilä I, Mayatepek E, Meissner T, Halestrap AP, Rutter GA, Kere J. Physical exercise-induced hypoglycemia caused by failed silencing of monocarboxylate transporter 1 in pancreatic beta cells. Am J Hum Genet. 2007 Sep;81(3):467-74. doi:10.1086/520960. Epub 2007 Jul 26. PMID:17701893; PMCID:PMC1950828.
Otonkoski T, Kaminen N, Ustinov J, Lapatto R, Meissner T, Mayatepek E, Kere J, Sipilä I. Physical exercise-induced hyperinsulinemic hypoglycemia is an autosomal-dominant trait characterized by abnormal pyruvate-induced insulin release. Diabetes. 2003 Jan;52(1):199-204. doi:10.2337/diabetes.52.1.199. PMID: 12502513.
