The typical gene for glucokinase can produce two different but very similar forms of glucokinase. One of these forms is typically produced in the brain and pancreas; the other form is produced in the liver.
This is because, among its other jobs, glucokinase is responsible for converting glucose to glycogen for storage in the liver, and its also responsible for signaling to our islet cells so that they know how much insulin and glucagon to produce.
People with one normal copy of the glucokinase gene and one copy that doesn't work as well generally have MODY 2- something whose classification as a diabetes is debatable. These people's bodies maintain blood sugar in a range as narrow as normal, but higher- they have a higher blood sugar set point that the body aims for. Attempting to treat it is difficult because of the body having an intact response to hypoglycemia, and that response kicking in at fairly high blood sugar levels. Fortunately, the risk of diabetes complications from MODY 2 is very low and so most doctors don't recommend treating it.
Although it doesn't predispose people to type 2 diabetes, when type 2 diabetes happens in a person who has MODY 2, it can be very hard to treat.
People with two copies of the glucokinase gene that don't work well may have neonatal diabetes, and there are also mutations of the gene that cause abnormally high production of insulin with hypoglycemia.