Type 2 diabetes and later Parkinson’s disease association reported

By Nicole MacKee
New research has identified an association between type 2 diabetes and the later development of Parkinson’s disease, but a leading Australian endocrinologist says the finding is no cause for alarm.

In a UK data-linkage cohort study of more than two million people with type 2 diabetes and six million people in a reference cohort, researchers found increased rates of subsequent Parkinson’s disease in the type 2 diabetes cohort (hazard ratio [HR], 1.32). The risk was greater in those with complicated type 2 diabetes (HR, 1.49) and in younger people aged 25 to 44 years (HR, 3.81).

Writing in Neurology, the researchers said that shared genetic predisposition – as suggested by the increased risk in the younger cohort – and/or disrupted insulin signalling as a result of lifestyle and environmental factors were possible mechanisms.

Professor Duncan Topliss, Director of the Department of Endocrinology and Diabetes at The Alfred, Melbourne, said: ‘Overall, the absolute prevalence of Parkinson’s disease in diabetes was 14,252 in 2,017,115 people. With a hazard ratio of 1.32 in type 2 diabetes, this means that Parkinson’s disease prevalence in people without diabetes is 5.3 per 1000. So, the excess Parkinson’s disease in type 2 diabetes is 17 cases in 10,000.

‘Although this is a statistically significant difference, it is a small absolute difference.’

Professor Topliss said the absolute difference was also small in younger people with type 2 diabetes with an additional 3.3 cases of Parkinson’s disease in 10,000.

For people aged over 75 years, there was no discernible increase in Parkinson’s disease in association with type 2 diabetes, he said.

Professor Topliss said the differences identified were statistically significant and pointed to a link.

‘The linkage could be genetic or environmental. It may not be some sort of shared mechanism, as the authors suggest, but a linkage disequilibrium between functionally unrelated genes. The mechanisms suggested are, at this stage, purely speculative,’  he told Medicine Today.

‘The absolute risk difference would not be discernible in clinical practice, and the association should not be cited to alarm people with type 2 diabetes because in the older patients the linkage was not seen, and it was still small in younger patients.’
Neurology 2018; 91: 1-4; doi: 10.1212/WNL.0000000000005771.