Lactose, or milk sugar, is a disaccharide made of two simple sugars – glucose and galactose – in a 1:1 ratio.

Following her illness, Mills was diagnosed with galactosaemia, a rare genetic disorder affecting up to one in 45,000 babies which prevents her body from turning galactose into glucose.

All mammals, including humans, make milk with carbohydrates in the same unique form: lactose, a sugar that is a fusion of two other sugars called galactose and glucose.

Yet Keasling claims his team is the first to develop a process that relies only on sugar—his yeast can make cannabinoids from galactose alone without requiring additional, more expensive ingredients.

In total, they needed to make 16 genetic modifications to transform galactose into inactive forms of THC or CBD.