Type 1 diabetes (T1D) is an autoimmune disease that leads to the destruction of pancreatic b cells and insulin deficiency. It is common in childhood and adolescence but can occur at any age. Although most cases lack a family history, first-degree relatives have a higher risk of developing T1D than does the general population. Within families, susceptibility depends on the degree of genetic identity with the proband. The highest risk is observed in identical twins. The disease concordance rate in twins can be up to 70% in studies with the longest follow-up period [1]. Although siblings have, on average, a lower prevalence of approximately 6%, this rate is still higher than the 0.4% observed in the white population in the United States, confirming a significant familiar clustering (ks = 6/0.4 = 15).
