The potential genetic link between ATM and metformin response will be investigated. Thus far it is unclear from the genetic studies how ATM deficiency affects an individual's metformin response - is their response greater or less than that of the general population? Similarly, magnitude of this response has not been quantified. There are anecdotal reports of patients with A-T who have had a marked improvement in glycaemic control with metformin use. Mouse model studies have indicated an increased response to metformin in heterozygous ATM deficient mice.