Genetics of canine diabetes mellitus part 1: Phenotypes of disease

•The multiple forms of human diabetes mellitus (DM) have different underlying causes.•Canine DM is likely to be heterogeneous, similar to human DM.•Identifying genetic risk factors is important to improve understanding of canine DM.•Greater understanding of canine DM aetiology will improve disease classification.•Increasing precise disease phenotyping will greatly benefit genetic studies.