Chikowore says there are many possible explanations for this, ranging from as yet undiscovered genetic variants to the physiological structure of the pancreas. The latter theory arises from research carried out in East Africa, which found that some men develop type 2 diabetes despite having a healthy weight. An ongoing study led by Uganda’s Medical Research Council, in partnership with UK researchers, is measuring the size of the pancreas in such men and assessing its function.

“These cases don’t appear to be related to fat, so we want to try and understand what’s going on,” says Chikowore. “Is it genetics? Or due to how the pancreas has developed? Some scientists think that it’s related to malnutrition in early life, impacting the development of the beta cells so they don’t produce as much insulin.”

As well as revealing the path to new treatments, understanding these cases could lead to improved screening tools. Currently, the gold-standard methods of diagnosing and assessing the progression of type 2 diabetes are fasting plasma glucose tests, which measure blood sugar after fasting, and the HbA1c blood test, which detects levels of a chemical compound called HbA1c that indicates blood sugar levels over time. But such tests are being shown to be ineffective in some populations.

Last year a major study highlighted that a significant number of people of African ancestry are diagnosed with type 2 diabetes much later than they might be, because they carry deficiencies in an enzyme called G6PD. This genetic variation is relatively common in parts of sub-Saharan Africa because it confers protection against severe malaria, but it also reduces levels of HbA1c, making it look like a person’s blood sugar levels are healthier than they actually are. T...