Genomic analyses of familial autoimmune Addison's disease
Lead Research Organisation:
Newcastle University
Department Name: Institute of Human Genetics
Abstract
Autoimmune Addison‘s disease (AAD) is a rare condition in which the immune system attacks the adrenal glands which normally produce essential steroid hormones. People with AAD are dependent lifelong on taking daily steroid medication for survival.
Like AAD, type I diabetes is an autoimmune disorder and results from an immune attack targeted, in part, against insulin in pancreatic cells. We know that variations in the insulin gene contribute to susceptibility to type I diabetes. In AAD, the target of the immune attack is an adrenal enzyme called 21-hydroxylase. Our hypothesis is that variations around the 21-hydroxylase gene might predispose an individual to AAD.
We already know that a complex series of variations exist around the 21-hydroxylase gene. The first part of my project is to see if these variations contribute towards AAD susceptibility. For the second part of my study, I will use gene-chips containing more than a million DNA markers scattered regularly across all the chromosomes to look for markers that are transmitted with Addison‘s disease in 25 families with 2 or 3 members affected by the condition. These studies should enhance our understanding of why AAD is so strongly inherited and will shed light on the mechanisms behind the disease.
Like AAD, type I diabetes is an autoimmune disorder and results from an immune attack targeted, in part, against insulin in pancreatic cells. We know that variations in the insulin gene contribute to susceptibility to type I diabetes. In AAD, the target of the immune attack is an adrenal enzyme called 21-hydroxylase. Our hypothesis is that variations around the 21-hydroxylase gene might predispose an individual to AAD.
We already know that a complex series of variations exist around the 21-hydroxylase gene. The first part of my project is to see if these variations contribute towards AAD susceptibility. For the second part of my study, I will use gene-chips containing more than a million DNA markers scattered regularly across all the chromosomes to look for markers that are transmitted with Addison‘s disease in 25 families with 2 or 3 members affected by the condition. These studies should enhance our understanding of why AAD is so strongly inherited and will shed light on the mechanisms behind the disease.
Technical Summary
Autoimmune Addison‘s disease (AAD) is amongst the rarest of the autoimmune diseases and has a high genetic load, with a lambda-sib of more than 150. However little of the genetic susceptibility has so far been accounted for, suggesting that there may be one, or a small number, of aetiological variants exerting very strong effects. Investigating AAD is important, as more than half of patients will develop a second autoimmune condition, suggesting that the alleles responsible for AAD will also contribute to susceptibility to other autoimmune conditions e.g. type I diabetes.
The major autoantigen for AAD is the steroidogenic enzyme, 21-hydroxylase. Variations at the insulin gene and thyrotropin receptor gene predispose to type 1 diabetes and Graves‘ disease, respectively. Therefore, it is plausible that variations in or around the gene encoding 21-hydroxylase will predispose to AAD. The 21-hydroxylase gene (CYP21B) is located in the MHC class III region, adjacent to the complement factor 4 gene, both contained within a known copy number variation. CYP21B is close to its own pseudogene, which also exists in several copy number states. In the first part of my study, I will use PCR-based approaches to determine whether structural variations at the CYP21 locus predispose to AAD, including quantitative real-time PCR, long range PCR and paralogue ratio testing. To pursue these studies, a unique sample resource is available to me, comprising 25 multiplex AAD families, 320 unrelated UK AAD probands and matching healthy controls.
In the second part of my project, I plan to perform a genome-wide linkage and association study, using SNP-chips containing 900,000 markers in members of the 25 UK and German kindreds with more than one affected AAD individual. I will analyse the data under the expert direction of genetic statistician Prof. Cordell, looking for the strength of the linkage signal and evidence for conserved haplotypes across different families. I will then take forward a series of the 200 most linked and associated markers to a replication experiment using a case-control design in the 320 unrelated AAD probands and 450 controls. This series of experiments should yield an unbiased insight into the genetic architecture of AAD for the first time.
This project provides a scientific opportunity to gain a greater understanding of autoimmune disease pathogenesis, and offers a medical opportunity since AAD has fatal consequences if the diagnosis is missed. A high penetrance AAD allele that predicts disease would be valuable in screening at risk individuals, such as children with type 1 diabetes.
The major autoantigen for AAD is the steroidogenic enzyme, 21-hydroxylase. Variations at the insulin gene and thyrotropin receptor gene predispose to type 1 diabetes and Graves‘ disease, respectively. Therefore, it is plausible that variations in or around the gene encoding 21-hydroxylase will predispose to AAD. The 21-hydroxylase gene (CYP21B) is located in the MHC class III region, adjacent to the complement factor 4 gene, both contained within a known copy number variation. CYP21B is close to its own pseudogene, which also exists in several copy number states. In the first part of my study, I will use PCR-based approaches to determine whether structural variations at the CYP21 locus predispose to AAD, including quantitative real-time PCR, long range PCR and paralogue ratio testing. To pursue these studies, a unique sample resource is available to me, comprising 25 multiplex AAD families, 320 unrelated UK AAD probands and matching healthy controls.
In the second part of my project, I plan to perform a genome-wide linkage and association study, using SNP-chips containing 900,000 markers in members of the 25 UK and German kindreds with more than one affected AAD individual. I will analyse the data under the expert direction of genetic statistician Prof. Cordell, looking for the strength of the linkage signal and evidence for conserved haplotypes across different families. I will then take forward a series of the 200 most linked and associated markers to a replication experiment using a case-control design in the 320 unrelated AAD probands and 450 controls. This series of experiments should yield an unbiased insight into the genetic architecture of AAD for the first time.
This project provides a scientific opportunity to gain a greater understanding of autoimmune disease pathogenesis, and offers a medical opportunity since AAD has fatal consequences if the diagnosis is missed. A high penetrance AAD allele that predicts disease would be valuable in screening at risk individuals, such as children with type 1 diabetes.
