Introduction:
The term glycosuria indicates the presence of simple sugars such as glucose, fructose, galactose, lactose, etc., in the urine. Kidneys play an important role in filtering the blood through which the excess sugars, if present in the blood, will be eliminated through the urine. The renal tubules play an important role in reabsorbing the sugars as well as excreting them if they are in excess amounts. But in cases of diseases or disorders affecting the kidney, especially the tubules, it would affect normal functioning resulting in excessive excretion of sugar in the urine despite normal or low blood sugar levels. Renal glycosuria is one of the rare conditions.
What Is Renal Glycosuria?
Renal glycosuria is a rare condition that is characterized by the excessive excretion of sugar in the urine. Renal glycosuria can occur even though the blood glucose levels are normal or lower than the normal range.
What Are the Other Terminologies Used to Define Renal Glycosuria?
The other synonyms of renal glycosuria include:
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Benign glycosuria.
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Nondiabetic glycosuria.
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Renal glucosuria.
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Primary renal glycosuria.
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Familial renal glycosuria.
What Is the Epidemiology of Renal Glycosuria?
It is estimated that it occurs in about 1 in 33,000 individuals among the general population. It does not show any gender discrimination affecting males and females equally. It is suggested to be more prevalent in conditions such as starvation and pregnancy. It can be inherited as both autosomal dominant and autosomal recessive inheritance patterns.
What Is the Difference Between Physiologic And Pathologic Glycosuria?
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Physiologic Glycosuria: It is a transient condition that is characterized by the excretion of sugar in the urine that occurs when a person consumes an excessive amount of carbohydrates. The presence of a small amount of glucose up to 0. 25 mg/ml in the random fresh urine is considered normal as it can occur due to overconsumption of carbohydrates or other physiological conditions.
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Pathologic Glycosuria: It is characterized by the excessive excretion of sugar in the urine due to improper kidney function or other mechanisms that are involved in normal glucose metabolism and excretion. The diagnosis of pathologic glycosuria is made when there is more than 0. 25 mg/ml of glucose in the random fresh urine.
What Is the Pathophysiology of Renal Glycosuria?
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Kidneys play an important role in glucose reabsorption and excretion. The glomerulus filters the glucose present in the blood, which is then reabsorbed by the renal tubules. Usually, the renal tubules of the properly functioning kidneys would reabsorb almost all the glucose filtered by the glomeruli leaving less than 25 mg/dl of glucose in the urine. This capacity of the renal tubules to reabsorb the glucose filtered by the glomeruli and prevent its excretion in the urine is called the renal threshold.
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When the amount of glucose filtered by the glomeruli exceeds the amount of glucose reabsorbed by the tubules, violating the renal threshold, the excessive unabsorbed glucose would be eliminated in the urine. This may occur due to two reasons, either due to the increased plasma sugar levels which occur in patients with diabetes mellitus or when the reabsorbing capacity of the renal tubules is affected due to any disease conditions affecting the kidneys.
What Is Transport Maximum for Glucose (TmG)?
TmG is the maximum capacity or point at which the increase in the concentration of glucose would not result in its excretion in the urine. If this capacity or point is crossed, the glucose will be excreted in the urine. In healthy adults and children, this value ranges from 260 to 350 mg/minute.
What Are the Types of Renal Glycosuria?
There are three subtypes of renal glycosuria; they are as follows:
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Renal Glycosuria, Type A - Is characterized by a low renal threshold and reduced TmG.
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Renal Glycosuria, Type B - Is characterized by a low renal threshold and normal TmG.
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Renal Glycosuria, Type 0- Is characterized by the complete absence of renal tubular reabsorption.
What Is the Etiology of Renal Glycosuria?
The causes of renal glycosuria include:
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Membrane Transport Disorders - These are usually inherited disorders affecting the transport of glucose across the cell membrane. These disorders commonly occur due to harmful genetic mutations affecting the membrane transport of glucose. In this condition, the body starts to recognize the low levels of glucose as normal and begins to excrete the glucose in the urine; hence the normal renal threshold is reduced to low levels.
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SLC5A2 Gene Mutation - The renal sodium-glucose cotransporter gene is responsible for mediating the activity of sodium-glucose cotransporters SGLT1 and SGLT2. These are the membrane proteins that mediate the reabsorption of glucose from the proximal convoluted tubules of the kidney. Genetic mutations in the SLC5A2 gene would result in loss of function of the SGLT1 and SGLT2, resulting in impaired reabsorption of glucose by the renal tubules.
What Are the Signs And Symptoms of Renal Glycosuria?
The majority of cases of renal glycosuria do not produce any apparent symptoms; only a few cases present with symptoms, and they are as follows:
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Polyuria (increased urine output).
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Polydipsia (excessive thirst).
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Enuresis (involuntary urination).
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Mild delays in growth and development during puberty.
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Dehydration (loss of excess body fluid).
How Is Renal Glycosuria Diagnosed?
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History: A thorough history of the symptoms should be collected from the patient as it provides a major clue in the diagnosis of the condition.
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Urinalysis:
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Urine Sugar Estimation - This would indicate the presence of excessive sugar in the urine to values more than 25 mg/dl.
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Blood Test:
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Blood Sugar Levels - This would indicate normal or low blood sugar levels.
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Genetic Testing:
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SLC5A2 Genetic Studies - This would indicate the mutation in the SLC5A2 gene.
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How Is Renal Glycosuria Treated?
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There is no specific treatment for renal glycosuria as it does not produce any life-threatening issues.
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The patients are advised to undergo routine urine tests to estimate their urine sugar levels and blood sugar levels.
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The patients should be advised to check for diseases such as diabetes mellitus, which is one of the major reasons for glycosuria, and hypoglycemics should be prescribed to prevent further complications.
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Genetic counseling - The affected person, as well as the family members, should be properly educated about the benign nature of the condition, and they should be reassured, as it would provide big mental support.
Conclusion:
Renal glycosuria is a rare disorder that is inherited as an autosomal dominant or recessive pattern. This condition is marked by the excessive excretion of simple sugars in the urine. The genetic mutations in the SLC5A2 gene play an important role in the etiology of this condition. The prognosis of this condition is good as it runs a benign course. The health care providers advise the patient to undergo routine urine and blood tests to keep the condition in check and also to rule out other complications.