| 1. |
- Asad, Samina
(författare)
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Genetic analysis of candidate susceptibility genes for type 1 diabetes
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Type 1 diabetes (T1D) is a complex disease where the pancreatic β-cells are destroyed in an autoimmune attack. For the patients, this leads to lifelong daily insulin treatment and increased risk for various kinds of complications. It is thought that both environmental as well as genetic factors act in concert to cause T1D. The Human Leukocyte Antigen (HLA) region located on chromosome 6 accounts for about 50% of the genetic risk to develop T1D. Several other genes are also known to contribute to disease risk. Paper I: Previous publications indicate that the programmed cell death 1 (PDCD1) gene (chr.2) is associated to various autoimmune diseases. PDCD1 is involved in maintaining self tolerance. The aim of our study was to test the involvement of the PDCD1 gene in T1D susceptibility. However, when two separate Swedish cohorts were analyzed no association or linkage was found between T1D and the PDCD1 gene. Nor did we observe any association in a meta-analysis with a previous study reporting association between PDCD1 and T1D. Paper II: We have in a previous study observed suggestive linkage to the chromosome 5p13-q13 region in Scandinavian T1D families. This region showed stronger evidence of linkage, when only the Swedish families were investigated. Genotyping of more than 70 markers in the Swedish families revealed two associated candidate genes: 5-hydroxytryptamine (serotonin) receptor 1A (HTR1A) and ringfinger protein 180 (RNF180). Association of both genes has been confirmed by us in Danish families. The two genes are in strong linkage disequilibrium with each other. However conditional analysis data suggest that HTR1A may be most strongly associated. Further, we report that HTR1A is expressed in human β-cells and α-cells. Paper III: The class II transactivator (CIITA) gene (chr.16) is crucial for MHC II gene regulation and has been reported to associate with susceptibility to a number of complex diseases. By genotyping SNPs in Swedish T1D cohorts and the combined control material from previous studies of CIITA we have observed significant difference in the genotype distribution for three markers in CIITA with respect to age, in the collected control material. This phenomenon was confirmed in an independent control material. After adjusting for age we detect association to T1D for two markers in our T1D material. Further, we observed interaction between markers in CIITA and the protective HLA DR15 haplotype. These findings suggest that a polymorphism in the CIITA gene area may be associated with type 1 diabetes susceptibility. Importantly, results also suggest that control groups should be properly matched for the cases. Paper IV: In complex diseases genes seldom act alone in disease susceptibility. Instead it is thought that genes may interact with each other. The aim of our investigation was to study the interaction of the most significantly associated genes in T1D (HLA-DRB1, HLA-DQB1, INS and PTPN22). This was done by comparing four different models for studying interaction; multiplicative and additive interaction models, Multifactor dimensionality reduction (MDR) model and Bayesian Networks (BN) model. Results indicate several interaction terms mainly in the additive model. Further, we show that the additive interaction model has the strongest prediction accuracy rate indicating that this is the model of preference. In summary, in order to better understand the cause of T1D the aim of this thesis was to identify single genes as well as gene-gene interactions which may influence the risk of T1D development.
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| 2. |
- Asad, Samina
(författare)
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Genetic analysis of type 1 diabetes susceptibilty
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Type 1 diabetes (T1D) is a multifactorial disease where the pancreatic beta-cells are destroyed in an autoimmune attack. For the patients, this in turn leads to lifelong daily insulin treatment and increased risk for various kinds of complications. It is thought that both environmental as well as genetic factors act in concert to cause T1D. The HLA region located on chromosome 6 accounts for about 50% of the genetic risk to develop T1D. However, several other genes are also known to contribute to disease risk. Paper I. The programmed cell death 1 (PDCD1) gene (chr 2q37) has previously been seen to be associated to various autoimmune diseases. The PDCD1 gene is believed to be involved in maintaining self tolerance by inhibiting T-cell activation, cellular proliferation and cytokine production. We wanted to test the hypothesis that the PDCD1 gene also was a T1D susceptibility gene. However, no association or linkage was found between T1D and the PDCD1 gene when two separate Swedish cohorts were analyzed. Nor did we observe any association in a meta analysis with a previous study reporting association between PDCD1 and T1D. Paper II. We have previously performed a genome wide linkage study on Scandinavian T1D families where we have detected suggestive linkage on the chromosome 5p13-q13 region. This region showed stronger evidence of linkage, when only the Swedish families were investigated. By typing more than 70 markers in this region in the Swedish families, we identified two associated candidate genes: Ringfinger protein 180 (RNF180) and 5-hydroxytryptamine (serotonin) receptor 1A (HTR1A). We have confirmed the association of these genes in Danish families. These genes are in strong linkage disequilibrium with each other but in preliminary data it appears that HTR1A may be most strongly associated. Further, we report that HTR1A is expressed in human beta-cells. In summary, in this thesis the aim was to identify additional genes which may influence the risk to develop T1D and we report association to two novel T1D susceptibility genes; RNF180 and HTR1A.
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| 3. |
- Asad, Samina, et al.
(författare)
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HTR1A a Novel Type 1 Diabetes Susceptibility Gene on Chromosome 5p13-q13
- 2012
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 7:5
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Tidskriftsartikel (refereegranskat)abstract
- Background: We have previously performed a genome-wide linkage study in Scandinavian Type 1 diabetes (T1D) families. In the Swedish families, we detected suggestive linkage (LOD less than= 2.2) to the chromosome 5p13-q13 region. The aim of our study was to investigate the linked region in search for possible T1D susceptibility genes. Methodology/Principal Findings: Microsatellites were genotyped in the Scandinavian families to fine-map the previously linked region. Further, SNPs were genotyped in Swedish and Danish families as well as Swedish sporadic cases. In the Swedish families we detected genome-wide significant linkage to the 5-hydroxytryptamine receptor 1A (HTR1A) gene (LOD 3.98, pless than9.8x10(-6)). Markers tagging two separate genes; the ring finger protein 180 (RNF180) and HTR1A showed association to T1D in the Swedish and Danish families (pless than0.002, pless than0.001 respectively). The association was not confirmed in sporadic cases. Conditional analysis indicates that the primary association was to HTR1A. Quantitative PCR show that transcripts of both HTR1A and RNF180 are present in human islets of Langerhans. Moreover, immunohistochemical analysis confirmed the presence of the 5-HTR1A protein in isolated human islets of Langerhans as well as in sections of human pancreas. Conclusions: We have identified and confirmed the association of both HTR1A and RFN180, two genes in high linkage disequilibrium (LD) to T1D in two separate family materials. As both HTR1A and RFN180 were expressed at the mRNA level and HTR1A as protein in human islets of Langerhans, we suggest that HTR1A may affect T1D susceptibility by modulating the initial autoimmune attack or either islet regeneration, insulin release, or both.
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| 4. |
- Gyllenberg, A, et al.
(författare)
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Age-dependent variation of genotypes in MHC II transactivator gene (CIITA) in controls and association to type 1 diabetes
- 2012
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Ingår i: Genes and Immunity. - Stockholm : Springer Science and Business Media LLC. - 1476-5470 .- 1466-4879. ; 76:2, s. 202-203
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Tidskriftsartikel (refereegranskat)abstract
- The major histocompatibility complex class II transactivator (CIITA) gene (16p13) has been reported to associate with susceptibility to multiple sclerosis, rheumatoid arthritis and myocardial infarction, recently also to celiac disease at genome-wide level. However, attempts to replicate association have been inconclusive. Previously, we have observed linkage to the CIITA region in Scandinavian type 1 diabetes (T1D) families. Here we analyze five Swedish T1D cohorts and a combined control material from previous studies of CIITA. We investigate how the genotype distribution within the CIITA gene varies depending on age, and the association to T1D. Unexpectedly, we find a significant difference in the genotype distribution for markers in CIITA (rs11074932, P=4 × 10(-5) and rs3087456, P=0.05) with respect to age, in the collected control material. This observation is replicated in an independent cohort material of about 2000 individuals (P=0.006, P=0.007). We also detect association to T1D for both markers, rs11074932 (P=0.004) and rs3087456 (P=0.001), after adjusting for age at sampling. The association remains independent of the adjacent T1D risk gene CLEC16A. Our results indicate an age-dependent variation in CIITA allele frequencies, a finding of relevance for the contrasting outcomes of previously published association studies.
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