Environmental factors

The recent increase in T1D incidence points to a changing global environment rather than variation in the gene pool, which require the passage of multiple generations (1).

Twin studies also provide evidence for the importance of environmental risk factors for T1D.

• T1D concordance rates for monozygous twins are higher than those for dizygous twins (approximately 30% vs. 10%, respectively)
• however, most monozygous twin pairs remain discordant. Thus, T1D cannot be completely genetically determined (1)

Environmental risk factors are thought to act as either ‘initiators’ or ‘accelerators’ of beta cell autoimmunity, or ‘precipitators’ of overt symptoms in individuals who already have evidence of beta cell destruction (1).

The T1D environmental risk factors that have received most attention are viruses and infant nutrition.

• viruses
  • Enteroviruses, especially Coxsackie virus B (CVB) is known to have systemic effects on the pancreas.
  • other viruses associated with T1D include: mumps, cytomegalovirus, rotavirus and rubella.
• infant nutrition
  • diabetic children are breast fed for a significantly shorter period than controls
  • early exposure to cow’s milk protein and the subsequent development of T1D (1)

The role of hygiene in the aetiology of T1D is also currently being explored

• it is hypothesized that delayed exposure to microorganisms due to improvements in standard of living hinders the development of the immune system
• further studies are needed to determine if improved hygiene can explain the temporal increase in the incidence of T1D worldwide (1)

Reference:

• (1) World Health Organization (WHO). Genetics and diabetes. Accessed on 15/10/2018