Although the pathogenic mechanisms of type 1 and type 2 diabetes are not similar, genes alone as the sole factor of diabetes is not sufficient. For example, identical twins have the same genetic sequencing, but if one of the twins may have type 1 diabetes, the other only has 50% of chance of diabetes. Similarly, if one of the twins has type 2 diabetes, than the chance of the other twin having the same diabetes is 75-90%. If the father is a type 1 diabetes patient, the chance of his offspring having the disease is 1/17; if the mother is a type 1 diabetes patient and gives birth after the age of 25, then the chance of the offspring having diabetes is only 1/100; if both parents are type 1 diabetes patients, then the chance of the offspring having the disease is 1/10~1/4. Therefore, genetic heritability of type 1 diabetes is not high.
If one of the parents has type 2 diabetes before the age of 50, then the chance of the offspring having the disease is 1/7. If type 2 diabetes occur after the age of 50, then the chance of the offspring having the disease is 1/13. However, if both parents have type 2 diabetes, there is a 50% chance that the offspring will also have type 2 diabetes. It may seem that the genetic factors of type 2 diabetes is high, but it is not 100%.
Even if the pathogenic role of genetics in type 1 or type 2 diabetes is uneven, it is not the main cause of disease, as environmental factors and lifestyle also play an important role. Maintaining good lifestyle, exercise regularly and eat a healthy diet are still the key factors in preventing diabetes.
Reference: American Diabetes Association