Summary 

Renal glycosuria is a rare type of condition in which glucose of the body starts getting excreted in the form of urine even if the body has normal or low glucose levels. While the kidney is functioning properly, glucose of the body starts getting excreted in the form of urine when the body has strangely high levels of glucose present in the blood of the body. Even so, in patients of renal glycosuria, glucose is excreted from the body in the form of urine because of inappropriate working of renal tubules. Renal tubules are particularly the elementary part of the filtration unit of the kidney. It is observed that in most of the cases of renal glycosuria there are not any types of symptoms or severe side effects visible in the patients of renal glycosuria. But in some of the critical cases the symptoms like polyuria, enuresis and delays in growth and maturation during public age have been noticed. The renal glycosuria is caused because of genetic changes in the SLC5A2 genes.

Introduction 

Renal glycosuria also known as nondiabetic glycosuria is a type of rare disorder in which general glucose of sugar is excreted from the body in the form of urine during the process of urination. This process even  takes place even when blood contains low or normal levels of glucose in it. Usually when the person’s kidneys are working properly then the glucose will be also released into the kidneys when the levels of glucose are very high in their blood. Even so, in the patients of renal glycosuria,  glucose is excreted in the form of urine because of the inappropriate working of renal tubules of kidneys, renal tubules are the primary components of the kidneys which performs the crucial function of filtering blood. Most of the people affected with this disorder don’t experience any type of specific symptoms or severe side effects. Reasons behind the occurrence of renal glycosuria by itself can be inherited in two types of patterns: an autosomal dominant pattern or an autosomal recessive pattern. 

Signs and symptoms of renal glycosuria

In the patients of renal glycosuria, glucose is excreted from their body in the form of urine during the process of urination. However, even if they have normal or low glucose levels in their blood. While the  blood travels from the kidneys, substances like calcium, glucose, sodium, water,  etc get filtered from its liquid portion. After this whole process newly filtered blood transported through tunes know renal tubules in the kidneys. The substances which can be helpful for the body such as sodium, water,calcium and glucose are then reabsorbed and get back to the bloodstream. The substances which are useless or harmful for the body will be left in the form of urine. In a person with completely healthy and functioning kidneys, glucose is only secreted when their  blood contains high levels of glucose in it. Although, in patients of renal glycosuria extra glucose of the body is excreted and the kidneys get trouble in reabsorbing glucose. 

Most patients of renal glycosuria are asymptomatic, which means they do nor consist of any specific symptoms. But, in some cases of renal glycosuria patients had reported symptoms like polyuria and polydipsia. In few critical cases of renal glycosuria some other symptoms such as involuntary urination also known as enuresis and mild delays in getting mature and grown while the time of puberty are also observed. If a patient of renal glycosuria gets pregnant or starving then this can result in causing low levels of fluid containment in their body (dehydration). It also causes specific chemicals substances (ketone bodies) build up in tissues. Additionally, fluids also build up because of excessive breakdown of fats, this process is known as ketosis. 

Causes 

The reason which is responsible for causing renal glycosuria is a genetic issue of membrane transport for that is an  abnormal renal transport syndrome. Disorders of membrane transport are noticeable by issue of movement that is transport of all the substances beyond the outermost layer of the cell which is known as cell membrane. It is possible that this can lead to dangerous genetic changes (mutation) which will cause specific proteins of the membrane to not form properly.

Due to the improper working of the renal tubules the deficiency of glucose levels in the body is caused. Along with the time the body starts to adopt these low levels of glucose as the recent normal levels and considers normal levels of glucose as excessive high levels, leading the body to excrete the glucose in the form of urine when levels are not extended. For some persons there is a decrease in maximum rate where the glucose can be absorbed again into the bloodstream. Renal glycosuria is particularly of two subtypes. Type A and Type B. Type A consists of a low renal threshold and decreased tubular maximum for glucose. Type B consists of a low renal threshold and normal tubular maximum for glucose. Additionally, there is also one more type of renal glycosuria which is type 0. This type of renal glycosuria doesn’t have renal tubular glucose reabsorption.  

The elementary reason behind the cause of renal glycosuria is dangerous change (mutation) in SLC5A2 gene. SLC5A2 gene is also known as the renal sodium- glucose cotransporter gene. 

A number of inheritance patterns are  proclaimed for renal glycosuria, and some more research is required to clear the pattern of inheritance. Generally it is observed that most of the renal glycosuria cases are inherited in autosomal recessive manner. Dormant genetic disorders appear when a dysfunctioning gene from both the parents is inherited by an individual. In the case, if an individual inherits one functioning gene and one non functioning gene for the condition, then the individual can be a carrier for the condition, however commonly symptoms are not visible. The risk of transferring dysfunctional genes by both carrier patients and as a result have an affected child is twenty five percent with each pregnancy. Having a child who is a carrier just like parents is around fifty percent with each pregnancy. The chances of having a child getting a functioning gene from their parents is twenty-five percent. The risks are common for both males and females. 

Autosomal dominant inheritance included with reduced penetrance has also been proclaimed. The meaning of reduced penetrance is a person suffering from genetic mutation with developed symptoms or non developed symptoms. Dominant genetic disorder happens when entirely a separate copy of a dysfunctional gene is needed to cause a specific disease. The dysfunctional gene can be inherited from the parents or can be the outcome of a change (mutated) gene in the affected person. The risk of transferring dysfunctional genes by the affected parents to an offspring is fifty percent in each pregnancy. The risks are common for both males and females.

It is possible that Individual who inherits dual copy of genes for renal glycosuria  (homozygosity) may encounter more critical symptoms, as compared with those who inherits single copy of gene mutation for renal glycosuria and a another copy with a diverse gene mutation for renal glycosuria in the same gene (compound heterozygotes). On the basis of such demonstration, a codominant inheritance pattern along with lowered penetrance has been currently offered as the best fit. Codominance happens when both the copies of genes are similarly explicit, with not either being dominant or recessive. 

A and B types of renal glycosuria have appeared in the members of the same family. In these types of cases, both the parents may consist of normal or either irregular renal tubular transportation of glucose. These types of exhibition provoke experts for recommending that other types of genetic or non genetic disorder may be responsible for causing renal glycosuria. 

Population affected from renal glycosuria 

There are around 1,33,000 patients of renal glycosuria all over the world. This disorder affects both males and females equally. It has been observed that most of the patients of renal glycosuria are not having any type symptoms visible in them (asymptomatic). In some severe cases of renal glycosuria some symptoms like dehydration and ketosis can be observed. These types of symptoms mostly occur when the patient is pregnant or starving. 

Disorders related to renal glycosuria 

Some of the features of these disorders can be most probably similar to the features of renal glycosuria comparison of both can be helpful in order to perform diagnosis correctly. 

One of the most common disorders of high glucose level in blood is diabetes mellitus. This disorder is caused because of less amount of insulin in the body or because of instability in the use of insulin. Insulin is particularly a type of hormone which helps the transportation of glucose into the cells for fulfilling  the energy requirement of the body. Insulin also gets into the liver and fat cells to get stored. If the amount of insulin is less in the body then it can increase the levels of glucose in that body (hyperglycaemia) and it can also increase the levels of glucose in the urine (glycosuria). Less amounts of insulin can cause fat metabolism and loss of functions to specific blood vessels. Some symptoms which can be included are polyuria, polydipsia and polyphagia. If these symptoms will not be treated properly then it is heavily possible that other complications might develop. However, the proper reason for the development of diabetes mellitus is not clear. Although, according to some researchers, genetic factors play a crucial role in the development of diabetes mellitus. 

One more genetic disorder similar to renal glycosuria is fanconi syndrome. Fanconi syndrome is a type of kidney condition, which occurs by its own as a part of genetic disorder, mostly cystinosis. It can be even caused due to other environmental factors such as kidney transplantation, drug toxicity, deficiency of vitaminD and exposure with heavy metals such as lead. The main reason behind its occurrence is the dysfunctional first portion of renal tubules which is known as proximal renal tubules. Its findings may consist of high acidic levels of blood and high levels of bicarbonates, glucose, phosphates and specifically amino acids in the urine. 

Hypophosphatemic rickets means a collection of conditions of proximal renal tubular dysfunction. They are noticeable by the reduction of phosphate and highly decreased levels of the active form of vitamin D. Some more complications such as decreased intestinal absorption of and bone related issues. Symptoms of these conditions include excess removal of phosphate from the body through the urine and extremely low phosphate levels in blood. Few other symptoms included in it our osteomalacia (bone softening) and pain bowing of legs. This condition can be  genetic or either developed because of a certain type of cancer. 

Diagnosis 

For the diagnosis of renal glycosuria some types or laboratory tests of blood and urine are performed. In the diagnosis test the levels of glucose in both urine and blood are checked. Generally it is recommended not to eat anything the night before the diagnosis. After completing this test, the patient will be ordered to have another test. This genetic testing for  changes (mutation) in the SLC5A2 gene will help the patients to determine risk of renal glycosuria In their family members.