Inherited metabolic disorders are genetic conditions that result in metabolic problems. This condition occurs due to the defective of the gene causes in deficiency of the enzyme. The enzyme is either not produced by the body at all or it is produced in the form that cannot be used by the body. The absence of certain enzyme may cause in buildup of toxic chemicals or something that the body needs may not be made. The code for producing an enzyme usually original -originated?- from a pair of genes. Individuals with inherited metabolic disorders inherited two copies of defective gene from their both parents as both parents are the carrier. Apart from that, autosomal recessive inheritance is a form of genetic transmission where a child who inherits two defective gene copies which cannot produce enough effective enzyme and develops the genetic metabolic disorder.
There are a lot of metabolic disorders that have been identified, and new ones continue to be discovered. Basically, metabolic disorders are divided into 2 main categories which are small molecules diseases and organelle diseases. Small molecules diseases include amino and organic acidemias, urea cycle disorders, fatty acid oxidation defects, carbohydrate metabolism defects, mitochondrial oxidative phosphorylation disorders, purine and pyrimidine metabolism disorders and pyruvate metabolism disorders. Small molecules diseases are often presented as more acutely and many lead to acute encephalopathy as they result in a small diffusible metabolite or precursors that accumulate in the brain. Moreover, four well-defined groups of genetic diseases in man can now be recognized in which the functions of an intracellular organelle are impaired: lysosomal storage diseases, mitochondrial disorders, endoplasmic reticulum storage diseases, and peroxisomal diseases. (Gouda, A. S., 2016).
METABOLIC DISORDER OF DIABETES
Diabetes, also known as Diabetes mellitus, is a condition where the plasma glucose concentration is raised chronically above normal levels which lead to a series of symptoms such as passing large quantities of sweet-tasting urine (Drury. P. L & Gatling. W, 2005). There are many factors leading to glucose abnormality, but the main cause is due to the lack or abnormal functioning of insulin (Bilous. R & Donnelley. R, 2010). In a healthy person, after glucose intake, insulin is required. Insulin is a hormone secreted by beta cells in the pancreatic islets of Langerhans in the liver cells to help increase glucose uptake by a process called glycogenesis. The secretion of insulin will then lower plasma glucose concentration when glucose is broken down into glycogen and stored in liver and muscle cells.
However, with diabetes, this system does not work. The two common symptoms are insulin deficiency and insulin resistance. If the pancreas cannot produce enough insulin, it is known as insulin deficiency. Besides that, insulin resistance happens when the cells of the body are resistant to the insulin and have trouble absorbing glucose. As time goes by, glucose level in the blood plasma will be elevated (hyperglycemia) and this condition will eventually develop into diabetes. There are many types of diabetes, though the most common types are Type 1 diabetes and Type 2 diabetes.
Type 1 diabetes is also known as juvenile diabetes, usually diagnosed in children and young adults. It is an autoimmune condition in which the immune system destroys beta cells in the pancreas (Daneman. D , 2006) that produce insulin. Thus, when production site of insulin is off, glucose in the body cannot be broken down and leads to high blood sugar level thus resulting in few complications as in -such as?- stroke, kidney disease, eye problem and nerve damage. It is proven that individuals with type 1 diabetes are ten times higher risk associating with cardiovascular diseases including myocardial infarction, stroke, angina, and need for coronary-artery revascularization than age-matched no-diabetic populations (Orchard et al., 2006).
In contrast, type 2 diabetes is insulin resistance where the normal insulin sensitivity is loss (Drury. P.L & Gatling. W, 2005). To be more specific, insulin cannot adequately control the use of sugar from food thus leading to sugar builds up in the blood (Vijan. S, 2010). Individuals which are older than 45 years old, with family history of type 2 diabetes and overweight are most likely to get type 2 diabetes. Over time, long term complications will be developed as in problems in kidneys, eyes, heart and nerves.
Aside from type 1 and type 2 diabetes, gestational diabetes is common during pregnancy and higher risk in pregnant women with obesity. Women diagnosed with gestational diabetes are most likely at risk for type 2 diabetes after giving birth. Gestational diabetes will affect both maternal and offspring. Maternal with gestational diabetes tends to give birth to large size baby and thus leading to difficulties during delivery. Besides that, it will also increase risk for preeclampsia and maternal death. On the other hand, offspring will be associated to stillbirth and abortion.
There are other types of diabetes, for instance monogenic diabetes and cystic fibrosis-related diabetes. Monogenic diabetes is a form of disease that inherited dominantly or recessively due to mutation in single gene (Hattersley, 2009). Cystic fibrosis-related diabetes is common in people with cystic fibrosis and they have both type 1 and type 2 diabetes symptom which are loss of islet beta cell mass and insulin deficiency (Zirbes. J & Milla. C. E, 2009).
Lack or absence of the insulin production in the body cause the glucose level to rise. This condition might affect other metabolic pathway such as lipid break down and protein break down as well. There are two types of diabetes, which are the type I and type II diabetes.
Type 1 diabetes mellitus is due to the autoimmune injury to the beta cells of the Islet of Langerhans in the pancreas where the beta cells were attacked by the body’s own immune system which cause a failure in insulin production. While type II diabetes is due to insulin resistance, in which the insulin produced by the body cannot be used properly by the cells due to a damage in the insulin-binding proteins’ receptor. (repeated) Glucose is a type of carbohydrates and it involves in four types of inter-related metabolic pathway which are glycolysis, gluconeogenesis, glycogenolysis and glycogenesis. While insulin is an enzyme in our body which plays an important role in regulating the level of glucose in our body. Since there is a lack in insulin in Type I diabetic patient and ineffective usage of insulin in Type II diabetic patient, the uptake of glucose from the blood will be lesser and this causes their body to use other energy sources such as lipids and proteins.
Low insulin level will cause an increased level of cAMP. Most of the metabolic pathway in our body are being balanced by the level of glucagon and epinephrine on one hand and by insulin on the other hand. In a normal person, both glucagon and epinephrine will activate adenylate cyclase and form cAMP. Meanwhile, insulin will produce phosphodiesterase which will the cleaves cAMP. In a diabetic patient, the level of insulin is very low, and this condition will cause the level of cAMP to increa
se, thus activating protein kinase A (PKA). cAMP and PKA will control the level of a bifunctional enzyme which is phosphofructokinase-2 and fructose-2,6-biphosphotase in glycolysis. So, when the level of cAMP and PKA is high, the enzyme will be phosphorylated and cause bisphosphatase to be activated. The activation of bisphosphatase will then cause the level of fructose-2,6-bisphosphatase to be lowered. Thus, glycolysis will be inhibited and gluconeogenesis is activated. Excess amount of cAMP will also cause glycogen synthesis to be inhibited and the break down of glycogen increases. When both gluconeogenesis and glycogen break down are activated in the liver, accumulation of excess glucose will occur.
In a diabetic patient, the lack of insulin in their body causes lipids and protein break down as well. In term of lipid break down, the high level of PKA and cAMP causes lipase to be activated and the break down of triacylglycerol occur. Free fatty acids and glycerol are produced from the break down process and they are released to the bloodstream. Glycerol will then undergo gluconeogenesis process while the fatty acids will undergo ketogenesis process. Both of these processes occur in the liver.
In term of protein degradation, amino acids from the break down of protein will be degraded. Amino acids will be converted to keto acids and enter TCA cycle as an intermediate. From the TCA cycle, malate will then be converted to become pyruvate and the pyruvate is then transaminated to become alanine. Alanine will then enter the liver and undergo gluconeogenesis. Thus, more glucose will be produced.
Clinical symptoms of diabetes can help in early detection. There are 3 classic symptoms encountered by diabetic patients which are excessive thirst, polyuria and weight loss. Excessive thirst in diabetic patients also known as polydipsia is due to dehydration as excess fluid is lost in the urine as well as salt and other electrolytes. The acute thirst in Type 1 diabetes may be almost unquenchable. Some might crave for sugar-containing fluid such as coca-cola to quench their thirst which make the situation worse.
Polyuria is a condition of excessive urine output from our body. Polyuria develops when the rate of glucose enters the proximal tubules of kidney exceeds the capacity of kidney to return glucose into the bloodstream. At this point, it is known as the renal threshold for glucose. Glucose spills over the urine as not all glucose can be reabsorbed into the blood circulation. The excess glucose in the urine causes more water to be drawn out into the urine due to osmotic effect. This leads to increase volume of urine in diabetic patients.
Weight lost in diabetic patients is due to body unable to get sufficient amount of glucose. Insufficient insulin prevent body cells from getting glucose from blood to use as energy source. This promotes glucose production by the liver where fats and protein are used as an alternative source for energy. Breakdown of fats and protein cause an overall reduction in diabetic patients’ body weight.
Besides the 3 classic symptoms mentioned above, diabetic patients may also experience other symptoms. Tiredness and lack of energy are common symptoms but not at all specific for diabetes. Blurry vision in diabetic patients is due to osmotic changes in the lens of eyes. However, blurry vision can be reduced once glucose abnormality has been corrected.
Although most diabetic patients will experienced the symptoms above, but these symptoms might not be mentioned when they develop slowly and over a long time of period. Early detection in diabetes is important as it can reduce the risk of developing complications of diabetes.
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