Biochemist who transformed the treatment of diabetes and was an expert witness in two high-profile murder trials
Vincent Marks, who has died aged 93, was a world expert in insulin and hypoglycaemia (low blood sugar). In 1985, his expert opinion helped to acquit Claus von Bülow of attempted murder, in a case that was dramatised in the film Reversal of Fortune (1990). On 21 December 1980, the American heiress Sunny von Bülow was discovered comatose in her bathroom, and she remained in a persistent vegetative state until her death in 2008. Her husband Claus, a Danish-born lawyer, was tried and found guilty of injecting her with insulin. On appeal in 1985, the defence showed there was no injection and, having scrutinised Sunny's medical notes, Marks said her collapse was likely to have been triggered by alcohol-induced fasting hypoglycaemia. "Sunny," he said, "was the victim of natural illness and her lifestyle." Marks' achievements and interest in hypoglycaemia began in the late 1950s when he created ways to detect low blood sugar and researched how the pancreas and glucose-management hormones work – vital knowledge that underpins the modern treatment of diabetes. From 1957 to 1962 he was a junior doctor in chemical pathology at the National Hospital for Neurology and Neurosurgery in London. He saw patients being diagnosed with dementia and other neurological conditions because they had confusion, anxiety and panic attacks, but they might have had hypoglycaemia, which has the same symptoms. The existing test for low blood glucose required laboratory apparatus and technical skill, so Marks developed a simpler method for doctors to use. It relied on the enzyme glucose oxidase, which made blood samples change colour according to the concentration of glucose. It was a forerunner of the glucose strips widely used in diabetes today. Marks worked with the South African researcher Ellis Samols to introduce a new technique from the US called insulin radioimmunoassay that could accurately measure the amount of insulin in the blood. This opened up the whole field of diabetes…