Emerging roles of rare and low-frequency genetic variants in type 1 diabetes mellitus

Abstract

Type 1 diabetes mellitus (T1DM) is defined as an autoimmune disorder and has enormous complexity and heterogeneity. Although its precise pathogenic mechanisms are obscure, this disease is widely acknowledged to be precipitated by environmental factors in individuals with genetic susceptibility. To date, the known susceptibility loci, which have mostly been identified by genome-wide association studies, can explain 80%-85% of the heritability of T1DM. Researchers believe that at least a part of its missing genetic component is caused by undetected rare and low-frequency variants. Most common variants have only small to modest effect sizes, which increases the difficulty of dissecting their functions and restricts their potential clinical application. Intriguingly, many studies have indicated that rare and low-frequency variants have larger effect sizes and play more significant roles in susceptibility to common diseases, including T1DM, than common variants do. Therefore, better recognition of rare and low-frequency variants is beneficial for revealing the genetic architecture of T1DM and for providing new and potent therapeutic targets for this disease. Here, we will discuss existing challenges as well as the great significance of this field and review current knowledge of the contributions of rare and low-frequency variants to T1DM.

Keywords: diabetes mellitus; endocrinology; genetics; molecular medicine; sequence analysis.

Figure 1

Candidate genes or loci of type 1 diabetes mellitus (T1DM) and their ORs (the yellow bars represent the rare and low-frequency genetic variants of T1DM).

Figure 2

The development of type 1 diabetes mellitus (T1DM). T1DM is caused by interplay between genetic and environmental factors, and epigenetics serves as a bridge between the two. To date, >50 candidate loci have been identified by genome-wide association study. The genetic variants within these risk regions can be divided into common variants, low-frequency variants and rare variants according to their different minor allele frequencies. The rare and low-frequency variants are likely to have more practical value in the treatment of T1DM because their ORs are larger than those of common variants. However, as the study of rare and low-frequency variants is an emerging research field, some hypotheses are still controversial and need further investigation. LD, linkage disequilibrium; MAF. minor allele frequency.