The clinical and genetic characterisation of young-onset diabetes

Maturity-onset diabetes of the young (MODY), due to hepatocyte nuclear factor 1 alpha mutations (HNF1A-MODY), is the most common form of monogenic diabetes presenting in young adults. An accurate genetic diagnosis of HNF1A-MODY has therapeutic implications for the patients and their family members. However, the majority of people with HNF1A-MODY are not referred for genetic testing and remain misdiagnosed as type 1 or type 2 diabetes.
As part of measures to address this misdiagnosis, over the last few years there have been efforts to define clinical features and biomarkers that can be used to identify those at high risk of HNF1A-MODY. Secreted hepatic proteins regulated by HNF1A are attractive candidates for diagnostic biomarkers that would be specific for this form of diabetes. Apolipoprotein M (apoM), C-reactive protein (CRP) and plasma glycan profile have all been investigated as biomarkers to improve selection of suspected MODY cases for genetic testing. In my thesis, I have addressed questions about the variation in apoM between different forms of diabetes and assessed the performance of hsCRP and plasma glycan profile to identify HNF1A-MODY in previously uninvestigated individuals with young-onset diabetes and in a non-European population. Additionally because CRP and plasma glycans are both important components of an acute inflammatory response, I examined the effect of haploinsufficiency of HNF1A in a standardised model of inflammation.
When investigating apoM, I showed that serum apoM levels are lower in HNF1A-MODY than controls, and have demonstrated for the first time that serum apoM provides good discrimination between HNF1A-MODY and type 1 diabetes. CRP and plasma glycan profile both performed well in identifying HNF1A-MODY cases in unselected young adults with diabetes. The results also suggested that both biomarkers have value for assessing the functional impact of novel HNF1A variants. I went on to examine the use of a low CRP for selecting those at risk of HNF1A-MODY in South Asian subjects with young-onset diabetes. This study suggests that the overall population prevalence of HNF1A-MODY is similar in South Asians to Europeans, but that MODY represents a lower proportion of those with diabetes (due to the higher prevalence of type 2 diabetes in South Asians). The specific selection strategy employed in this study was not successful in identifying subjects at high risk of HNF1A-MODY (only 3% of those sequenced had mutations), suggesting that additional clinical and biochemical features will be required in addition to CRP to distinguish South Asians at high risk of HNF1A-MODY.
Lastly, using endotoxaemia as a standardised model of acute inflammation for the first time in HNF1A-MODY, I have shown that despite low baseline levels, subjects with HNF1A-MODY had peak stimulated CRP levels comparable to non-diabetic controls. An attenuated cytokine response was observed in HNF1A-MODY, which requires further investigation. This is also the first report of inflammation-associated changes in plasma and white cell membrane glycan profile in diabetes.
This research work adds substantially to current understanding of performance of HNF1A-MODY biomarkers, a critical step before their clinical translation. The work presented also provides novel insights into the regulation of the acute inflammatory response in HNF1A-MODY.