Sample Paper: “Genetic Factors of type-1 diabetes”

Type-1 diabetes is a multi-factorial disease that is associated with strong genetic components and is found to be caused by the destruction of pancreatic ?-cells by the autoimmune failure. There are a total of eighteen regions in our chromosomes that code for specific genes that have been linked to type-1 diabetes. These regions are termed insulin dependent diabetes mellitus (IDDM) 1-18. IDDM1 by far has been the most studied and it is located in chromosome 6. Within this region, specific genes termed human leukocyte antigen (HLA) genes are found at 6p21. These HLA genes are one of the major genes associated with this disease. However, more over 40 non-HLA vulnerability gene markers have also been confirmed and associated with the genetic failure leading to type-1 diabetes such as INS (insulin) genes which are located in IDDM2 on chromosome 11 that have tandem repeats. There are four classes of HLA genes: Class I, II, III, and IV. Class II HLA genes are said to have the strongest association with the type-1 diabetes. Class II HLA genes have different alleles that give rise to the variability of these genes. The loci have been identified as HLA-DQB, HLA-DRB, and HLA-DQA and are said to be involved in the predisposition of type-1 diabetes. Certain strains of the HLA-DQ and HLA-DR genes have been associated with the increase risk of type-1 diabetes, while different variations in HLA-DQA have been found to have a protective response towards the autoimmunity of T cells.

Given these discoveries and developments, children that inherit the HLADR3/4-DQ8 from their parents have a really high risk of developing this disease. These children are susceptible of the developing type-1 diabetes before they are five years old due to having an autoimmune response.
Children with the HLA-risk genotypes DR3/4-DQ8 or DR4/DR4 who have a family history of type-1 diabetes have more than a 1 in 5 risk for developing islet auto-antibodies during childhood, and children with the same histo-compatibility leukocyte antigen (HLA) risk genotype but no family history have approximately a one in 20 risk. Determining extreme genetic risk is a prerequisite for the implementation of primary prevention trials, which are now underway for relatives of individuals with type-1 diabetes.
T helper cells, cytotoxic T cells, natural killer cells and B cells all play a role in the mechanism in which HLA genes use in the destruction of pancreatic beta cells. When a T cell recognizes fragments of pancreatic beta cells on the HLA complex of antigen presenting cells, it signals an autoimmune response. The T cell then could stimulate B cells to produce antibodies to attack the pancreatic beta cells, or stimulate cytotoxic T-cells to attack as well. Natural killer cells could also interact with HLA genes through the KIR receptors, and depending on what signals are received, it could stimulate protection or disruption of the beta cells. T regulatory cells play a role in the prevention of an autoimmune response, but mutations in the Fox gene alters this function thus it is more likely to have an autoimmune response.

Environmental Factors
Research has suggested that environmental factors such as viruses and climate may have an effect in the risks of developing type-1 diabetes. A study that was performed in 1972 by the British Diabetic Association showed there was a correlation with the increasing number of new type-1 diabetes cases during the winter and fall. Other research performed in Denmark and Massachusetts also demonstrate seasonal peaks of type-1 diabetes especially in colder weather. Environmental factors can also be seen in the differences that between type-1 found amongst the many Caucasian groups in other parts of the world. Migration to different countries and continents has ensured that they acquire the specific traits in those areas.

In 1988, there was an increase in type-1 diabetes case after there was an outbreak of mumps. A correlation between the area of mumps and outbreaks of type-1 diabetes was observed. One possible explanation for the increase in type-1 diabetes during cold weather could be that in colder weather, the immune system is weaker and our bodies acquire more viruses hence the chances of genetic mutations increasing.

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