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International Textbook of Diabetes Mellitus, 4th Ed., Excerpt #169: Molecular Genetics of Type 1 Diabetes Part 6

Other genetic markers—the “missing heritability": Collectively the confirmed T1DM risk loci account for approximately 70% of disease heritability, with around 40–50% being attributed to the HLA genes. These figures are well in excess of the 10–20% of heritability of other complex diseases that can be explained by genetic factors. Experience from GWAS suggests that overall disease risk is likely to be influenced by many genes, most having a weak biologic effect. This may be due to the subtle effects of risk alleles on gene function or the modest contribution of individual gene products to the biologic pathways involved in disease pathogenesis. None of the confirmed T1DM risk variants have complete penetrance and are therefore neither necessary nor sufficient for disease to develop. This makes it difficult to use genetic profiling to predict disease risk as T1DM can develop in the absence of susceptibility variants and does not always occur in subjects with known risk markers.

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International Textbook of Diabetes Mellitus, 4th Ed., Excerpt #168: Molecular Genetics of Type 1 Diabetes Part 5

Linkage studies identify regions of the genome that are shared more frequently than would be expected by chance by relatives affected by a particular disease. Most studies analyze affected sibling pairs and utilize genetic markers that are scattered throughout the genome at moderate density, typically microsatellites. A significant excess of allele sharing identical by-descent (IBD) in affected sibpairs suggests that the region containing the marker locus also contains a disease susceptibility locus. The first linkage scan for T1DM identified 20 chromosomal regions with suggestive evidence of linkage to disease, including the HLA and INS gene regions.

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