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After a carbohydrate-rich meal, the blood glucose levels rises. Glucose sensors, located in the pancreas, sense the rise in blood glucose, triggering the release of insulin from pancreatic beta cells. Insulin acts primarily on the liver, muscle, and adipose tissue, causing the uptake of glucose by these tissues. This results in the restoration of blood glucose to normal levels. In people with diabetes, blood glucose levels remain elevated. The sustained rise in blood glucose seen in diabetic patients can be the result of absence of insulin production or unresponsiveness of tissues to the hypoglycemic effects of insulin. In either case, diabetic patients are cannot properly metabolize glucose. Thus, diabetic patients are said to be in a state of relative starvation. The most frequent forms of diabetes are type 1 diabetes (or insulin-dependent diabetes mellitus) and type 2 diabetes (noninsulin-dependent diabetes mellitus). Type 1 is an autoimmune disease in which a patient's immune system mounts an attack on their own pancreatic beta cells. As a result, the pancreas of patent's with type 1 diabetes fail to secrete insulin in response to hyperglycemia. Type 2 diabetic patients, in contrast to type 1, are capable of sufficient insulin production. However, in these patients, the tissues have become insensitive to the effects of insulin. Type 2 diabetes is associated with obesity and is much more common (95%) than type 1 (5%). In this paper, a case study will be used to discuss the etiology (genetic and environmental), diagnosis, and treatment of type 1 (NIDDM) and type 2 (IDDM) diabetes mellitus.
CASE STUDY 1
Megan, a 10 year old female, presents to the doctor's office with an approximate 10 pounds weight loss over the last few weeks, nausea, increased thirst and urination. Her father has been living with type 1 diabetes mellitus for 10 years and one cousin was diagnosed with type 1 diabetes mellitus at age 13 months. Biopsies performed on the pancreas revealed damage to pancreatic beta cells. Lab results showed severely low levels of insulin.
Type 1 Diabetes: Genetic Factors
Type 1 diabetes is an autoimmune disease in which a person's immune system mounts an attack on the insulin-producing beta cells of the pancreas. The cause of the disease is usually endogenous (inheritance) but exogenous (environmental) influences can make a person who is genetically predisposed even more susceptible to developing the disease (Owerbach, 1993).
Numerous studies have been conducted that has shed some light on the genetic risk factors of type 1 diabetes mellitus. Eighteen regions in the human genome (IDDM1 - IDDM18) have been shown to be correlated with an increase in the risk of type 1 diabetes (Owerbach, 1993). More specifically, the HLA genes located within the IDDM1 region has been the main point of interest in many studies. Studies suggest that variations in these genes results in the predisposition to type 1 diabetes. Although these genes found in the IDDM1 region has been the most thoroughly studied of all the 18 regions, it acts in concert with other genes to influence the onset of type 1 diabetes; thus it should not be looked at as an isolated risk factor (Owerbach, 1993)
WHAT ARE HLA GENES?
The HLA genes are located on chromosome 6. The transcription of HLA genes leads to the expression of major histocompatibility complex (MHC) glycoproteins. MHC is utilized by cells of the immune system (macrophages, dendritic cells, B cells) to present antigens to T cells. This results in an immune response by the body's immune system (Bennett, 1995).
HOW ARE HLA GENES LINKED TO TYPE 1 DIABETES?
Studies have shown that an increased risk of developing an autoimmune disease such as type 1 diabetes is linked to the alleles of HLA genes in the body. In an ideal person, the expression of HLA genes leads to the production of MHC that only presents foreign and infectious organisms (Bennet, 1995). However, different alleles of the HLA gene have been identified which express MHC proteins that present the body's own amino-acid chain to T cells. In these cases, an autoimmune disease sometimes follows because of an immune attack on a person's own cells (Bennet, 1995). HLA-DR, HLA-DQ, and HLA-DP are HLA alleles that have been found to have a strong correlation to an increased predisposition to type 1 diabetes (Owerbach, 1993). In addition to HLA genes, IDDM1 as well as the other IDDM loci also contain genes associated with diabetes (Owerbach, 1995). Thus, it remains difficult to pinpoint the exact problem alleles. A dual inheritance of alleles is speculated to be involved in the increased risk of type 1 diabetes (Owerbach, 1993).
EXTERNAL FACTORS - diet (obesity) and viral infection can increase the risk of type 1 diabetes in a person who is already genetically predisposed to the disease.
Type 1 diabetes is an autoimmune disease in which the body's own immune cells attack and destroy pancreatic beta cells, leading to insulin insufficiency. Damaged pancreatic beta cells seen in this patient is indicative of type 1 diabetes mellitus. The symptoms (polyphagia, polyuria, weight loss) exhibited by the patient, along with close family members that have been diagnosed with type 1 diabetes reinforces a type 1 diabetes diagnosis. Further lab work is usually done to assess the patient's blood glucose, acid, and insulin,
Type 1 diabetes patients have a deficiency in the production of insulin. Thus, insulin replacement is mandatory to treat hyperglycemia. Insulin administration must be monitored in order to prevent a precipitous decline in blood glucose. Potassium depletion is also a symptom that always exists in type 1 diabetic patients. Therefore, repletion of potassium is also necessary. Caution must be taking when re-administering potassium because high levels of potassium can disrupt cell resting membrane potential
CASE STUDY 2
A 32-year-old Mexican American woman with a history of obesity, hyperlipidemia reports to her physician with chronic fatigue. Laboratory results were high for arterial blood gas with pH of 7.16. Her blood glucose level is greater than 270 mg/dl, and is positive for ketonemia. There is also absence of pancreatic beta cell antibodies and her insulin levels seem to be normal.
TYPE 2 DIABETES: GENETIC FACTORS
Food intake and exercise are the main risk factors for developing type 2 diabetes because the majority of effected individuals are obese. Type 2 diabetes also has a genetic component; however, this area is vaguely understood.
A combination of genes is speculated to be involved in the development of type 2 diabetes. However, it has been difficult for scientist to link these gene combinations with an increased risk of developing diabetes. Studies have identified a major gene that maybe associated with an increased susceptibility to type 2 diabetes: Palpain 10 (CAPN10) (Nestorowicz, 1998).
WHAT IS CALPAIN 10 AND HOW IS IT LINKED TO TYPE 2 DIABETES?
Calpain 10 is an enzyme that breaks down proteins into more or less active forms(Nestorowicz, 1998). They are involved in cell proliferation, intracellular signaling, and differentiation. The gene for the enzyme is located on chromosome 2 (Nestorowicz, 1998). According to research, variation in the 10 gene has been shown to triple the risk of developing type 2 diabetes in Mexican-Americans. CAPN10 has a complex connection with diabetes in that risk is not due to a single variation but to interactions between several variations of genes. These interactions don't always increase risk; in fact they can decrease or have no effect (Nestorowicz, 1998). The highest risk combination, called 112/121 has been linked with increased susceptibility in Mexican Americans (Nestorowicz, 1998) . Due to the expression of CAPN10 in the pancreas, scientists believe that the enzyme increase insulin secretions, which eventually leads to decreased tissue sensitivity to the hypoglycemic effects of insulin.
Consistent overconsumption of food may result in frequent secretion of insulin. Over time, tissues become insensitive to the effects of insulin, resulting in hyperglycemia or elevated blood glucose. Exercising muscles require glucose for energy. This can be another route by which blood glucose can be lowered. Exercise can also increase tissue sensitivity to insulin. Thus, exercise is an effective treatment for type 2 diabetes, whereas living a sedentary lifestyle can lead to the development of type 2 diabetes.
Elevated blood glucose is a classic sign of diabetes The patient's elevated blood glucose shows inefficiency in the ability to metabolize glucose. Because her insulin level is normal, we can rule out type 1 diabetes as a possible cause because this form of diabetes is associated with complete absence of insulin production. Absence of insulin antibodies further confirms this idea. Ketonemia is common in diabetic patients because the body begins to break down fats for energy in the absence of glucose. Fatty acid oxidation lags behind the remarkable increase in the release of fatty acid, and as a result, excess fatty acids are converted to ketone bodies, resulting in the decline in blood pH. This explains the ketonemia and low blood pH observed in this patient. Her obese state confirms a type 2 diabetes diagnosis because it is a trait associated with the onset of the disease.
Although type 2 is non-insulin dependent, patients still require short-term treatment with insulin. Short-acting insulin is usually administered before a meal along with long-acting insulin twice a day. Blood glucose must be monitored closely to prevent hypoglycemia.
The most effective treatment for type 2 diabetes is diet modification, to reduce caloric intake (less fat and carbohydrates), along with exercise. A modified diet can lead to reduced blood glucose and exercise can increase tissue sensitivity to the hypoglycemic effects of insulin.