Renal glucosuria in schoolchildren: Clinical characteristics

Renal glucosuria in children

The kidneys play a critical role in maintaining glucose homeostasis. Under normal renal tubular function, most of the glucose filtered from the glomeruli is reabsorbed in the proximal tubules, leaving only trace amounts in the urine. Glycosuria can occur as a symptom of generalized proximal tubular dysfunction or when the reabsorption threshold is exceeded or the glucose threshold is reduced, as seen in familial renal glycosuria (FRG). FRG is characterized by persistent glycosuria despite normal blood glucose levels and tubular function and is primarily associated with mutations in the sodium/glucose cotransporter 5A2 gene, which encodes the sodium-glucose cotransporter (SGLT) 2. Inhibiting SGLTs has been proposed as a novel treatment strategy for diabetes, and since FRG is often considered an asymptomatic and benign condition, it has inspired preclinical and clinical studies using SGLT2 inhibitors in type 2 diabetes. However, patients with FRG may exhibit clinical features such as lower body weight or height, altered systemic blood pressure, diaper dermatitis, aminoaciduria, decreased serum uric acid levels, and hypercalciuria. Further research is needed to fully understand the pathophysiology, molecular genetics, and clinical manifestations of renal glucosuria.

A Case of Tubulointerstitial Nephritis With Uveitis Diagnosed From Isolated Glucosuria Detected During School Urinary Screening

We report a case of tubulointerstitial nephritis with uveitis (TINU) diagnosed from isolated glucosuria detected during school urinary screening. The patient was a 12-year-old girl in whom glucosuria was detected during school urinary screening using a dipstick; however, urinary protein and occult blood were negative. There were no preceding symptoms of infection or medication. The patient visited the Fujita Health University Okazaki Medical Center two weeks after the school urinary screening for further examination. No edema or skin rash was observed. A urine test showed urinary glucose was positive and urinary β2-microglobulin was high; other values were almost normal. Mild renal dysfunction was observed. There was no hyperglycemia or high HbA1c level; therefore, diabetes mellitus was ruled out. Various autoantibody tests were negative, and the angiotensinogen-converting enzyme level was within the normal range. The patient was clinically diagnosed with idiopathic tubulointerstitial nephritis without a renal biopsy. Renal dysfunction tended to improve gradually after the first visit. Three months after the first visit, conjunctival congestion appeared in the right eye, and the patient was diagnosed with uveitis and eventually with TINU. When performing detailed examinations for urinary glucose, it is necessary to differentiate kidney disease as well as diabetes mellitus. Moreover, it is necessary to recognize that even if the urine dipstick test is negative for protein, it may be positive for low-molecular-weight protein.

Clinical features of pediatric renal glucosuria cases due to SLC5A2 gene variants

BACKGROUND

Familial renal glycosuria (FRG) is a rare renal tubular disorder characterized by a variable loss of glucose in the urine despite normal blood glucose levels, which is seen in a condition in which other tubular functions are preserved. In this study, the molecular and clinical characteristics of pediatric FRG cases due to SLC5A2 gene variants were defined.

METHODS

Demographic features, diagnostic tests, and molecular analyses of patients with a diagnosis of FRG cases due to SLC5A2 gene variants were retrospectively analyzed between 2016 and 2019.

RESULTS

The data of 16 patients who were clinically and genetically diagnosed with FRG in a 4-year period were analyzed. Seven (44%) of the cases were female and 9 (56%) were male. The median age at diagnosis was 6 years old (2 months old to 17 years old). Neuromotor development was found to be appropriate for the age in each case. Systemic blood pressure was evaluated as normal. A homozygous pathogenic variant in the SLC5A2 gene was detected in 14 patients in the genetic examination. A heterozygous variant was detected in one patient. In the other patient, two different heterozygous pathological variants were found in the SLC5A2 gene.

CONCLUSIONS

It was revealed that growth and development were normal in children with glucosuria due to variations in the SCL5A2 gene. Renal function tests and urinary amino acid excretion were also within normal values. In our case series, the most common genetic variation in the SCL5A2 gene was the A219T (c.655G>A) variant.

Hereditary tubulopathies accompanying polyuia

Tubulopathies are a group of heterogeneous diseases that are manifested in the malfunction of the renal tubules. This review addresses tubulopathies associated with polyuria syndrome, namely renal glucosuria syndrome, nephrogenic diabetes insipidus and pseudohyperaldosteronism. Types of renal glucosuria are described, namely: type A, type B and the most severe type 0. Type A is characterized by a low filtration threshold and low glucose reabsorption. The type of inheritance is autosomal recessive. Type B, autosomal dominant, is characterized by uneven activity of glucose transport, in which its reabsorption is reduced only in some nephrons. That is, normal reabsorption of glucose is maintained, but the filtration threshold of the latter is reduced. Type 0 with a severe course is characterized by complete inability of epithelial cells of the proximal tubules to reabsorb glucose. Nephrogenic diabetes insipidus is a rare inherited disease caused by impaired response of the renal tubules to antidiuretic hormone (ADH). Depending on the degree of inability to concentrate urine, there are complete and partial forms. It is divided into nephrogenic diabetes insipidus type I (X-linked recessive); nephrogenic diabetes insipidus type II (autosomal recessive and autosomal dominant) and nephrogenic diabetes insipidus syndrome with dementia and intracerebral calcifications (type of inheritance remains unknown). Children with autosomal recessive type of inheritance suffer from the more severe disease course. Pseudohypoaldosteronism is characterized by a special condition of the renal tubules which is due to insufficient sensitivity of the tubular epithelium to aldosterone, which in turn leads to hyperaldosteronism, the development of hyponatremia, metabolic acidosis with hyperkalemia, polydipsia and polyuria, decreased sodium reabsorption and retardation of the child's physical development. The classification includes three syndromes of pseudohypoaldosteronism, namely: type I (PHA1), which is divided into PHA1A (autosomal dominant, renal), PHA1B (autosomal recessive, systemic); type II (PHA2; Gordon’s syndrome), type III (secondary), which develops as a result of renal pathology.

Can we contribute to the diagnosis of diabetes and regulation of blood glucose by increasing the urologists’ awareness of glucosuria?

Aims:

Diabetes mellitus is a progressive, chronic, systemic, metabolic disease that must be managed effectively. Its prevalence is increasing rapidly. We investigated whether urologists’ awareness and recognition of glucosuria contributed to the diagnosis of diabetes and regulation of blood glucose.

Methods:

A total of 39,053 patients were retrospectively evaluated between January 2018 and February 2019. Of them, 16,211 had undergone urinalysis for varied reasons. Glucosuria was semi-quantitatively measured as (+), (++), (+++), and (++++). Patients were assessed in terms of whether they had been referred to endocrinology or internal medicine departments within the 15 days and the presence/absence of a previous or new diagnosis of diabetes mellitus by measuring blood glucose and HgbA1c levels.

Results:

Glucosuria was detected in 665 patients (4.1%), of whom 495 were included in the study. 417 (84.2%) had been previously diagnosed with diabetes mellitus, and 56 (11.3%) newly received a diabetes mellitus diagnosis. Blood glucose and HbA1c values were normal in 22 (4.4%) patients with glucosuria. HgbA1c value was determined as 7 or above in 381 (91.3%) of 417 cases with a previous diabetes mellitus diagnosis.

Conclusion:

Referring all patients detected to have glucosuria in the spot urine test at any time regardless of fasting/non-fasting to the relevant departments can contribute to the diagnosis and treatment of diabetes mellitus disease.

Clinical and genetic analysis in a family with familial renal glucosuria: Identification of an N101K mutation in the sodium-glucose cotransporter 2 encoded by a solute carrier family 5 member 2 gene

We report the identification of a mutation in the solute carrier family 5 member 2 (SLC5A2) gene, which encodes sodium-glucose cotransporter 2, in a family with familial renal glucosuria. The proband was a 26-year-old Japanese man referred to the diabetes division with repeated glucosuria without hyperglycemia. His mother, uncle and grandfather also had a history of glucosuria. A heterozygous missense mutation (c.303T>A:p.N101K) in SLC5A2 was identified in the patient and his mother, but not in 200 chromosomes from 100 healthy and unrelated individuals, or in 3,408 Japanese individuals in the Tohoku Medical Megabank. Furthermore, bioinformatics software predicted that this lesion would be pathogenic. We infer that the mutation led to clinically relevant sodium-glucose cotransporter 2 dysfunction. The patient showed no symptoms of hypoglycemia, but continuous glucose monitoring confirmed asymptomatic hypoglycemia.

Foveal avascular zone area analysis in juvenile-onset type 1 diabetes using optical coherence tomography angiography

PURPOSE

Optical coherence tomography angiography (OCTA) was performed on patients with juvenile-onset type 1 diabetes (T1DM) but with no diabetic retinopathy to measure the foveal avascular zone (FAZ) area.

STUDY DESIGN

Retrospective single-facility study METHODS: Twenty-nine patients (58 eyes) with juvenile-onset T1DM were studied. Images (3 mm x 3 mm cube centered on the fovea) were acquired using an OCTA device. Age at examination was 16.1 ± 8.7 years; onset age was 6.4 ± 3.5 years; duration of diabetes was 9.7 ± 8.3 years. Twenty-four age-matched healthy individuals were studied as controls.

RESULTS

FAZ area was significantly larger in T1DM patients than in controls (0.29 ± 0.09 vs. 0.25 ± 0.08 mm², P = 0.0234). Parafoveal vessel density was not significantly different between patients and controls (50.43 ± 4.24 vs. 50.07 ± 4.64, P = 0.8842). By generalized linear model analysis, annual HbA1c (P = 0.0190), number of serious hypoglycemic attacks (P = 0.0210), and onset age (P = 0.0447) were identified as variables significantly associated with FAZ area. Age, gender, duration of disease, total cholesterol, high or low-density lipoprotein, triglycerides, and body mass index were not significantly associated with FAZ area.

CONCLUSION

Patients with juvenile-onset T1DM and no diabetic retinopathy had increased FAZ, but no significant difference in parafoveal vessel density compared to healthy controls. Larger FAZ area was associated with higher annual HbA1c, more episodes of severe hypoglycemic attacks, and older onset age.

Renal glucosuria is associated with lower body weight and lower rates of elevated systolic blood pressure: results of a nationwide cross-sectional study of 2.5 million adolescents

BACKGROUND

Gene coding mutations found in sodium glucose co-transporters (SGLTs) are known to cause renal glucosuria. SGLT2 inhibitors have recently been shown to be effective hypoglycemic agents as well as possessing cardiovascular and renal protective properties. These beneficial effects have to some extent, been attributed to weight loss and reduced blood pressure. The aim of the current study was to evaluate the prevalence of renal glucosuria amongst a large cohort of Israeli adolescents and to investigate whether renal glucosuria is associated with lower body weight and lower blood pressure values.

METHODS

Medical and socio-demographic data were collected from the Israeli Defense Force's conscription center's database. A cross-sectional study to evaluate the association between conscripts diagnosed as overweight [BMI percentiles of ≥ 85 and < 95 and obesity (≥ 95 BMI percentile)] and afflicted with renal glucosuria was conducted. In addition, we assessed the association of renal glucosuria with elevated diastolic and systolic blood pressure. Multinomial regression models were used.

RESULTS

The final study cohort comprised 2,506,830 conscripts of whom 1108 (0.044%) were diagnosed with renal glucosuria, unrelated to diabetes mellitus, with males twice as affected compared to females. The adjusted odds ratio for overweight and obesity was 0.66 (95% CI 0.50-0.87) and 0.62 (95% CI 0.43-0.88), respectively. Adolescents afflicted with renal glucosuria were also less likely to have an elevated systolic blood pressure of 130-139 mmHg with an adjusted odds ratio of 0.74 (95% CI 0.60-0.90).

CONCLUSIONS

Renal glucosuria is associated with lower body weight and obesity as well as with lower rates of elevated systolic blood pressure.

A novel compound heterozygous mutation in SLC5A2 contributes to familial renal glucosuria in a Chinese family, and a review of the relevant literature

Familial renal glucosuria (FRG) is a rare condition that involves isolated glucosuria despite normal blood glucose levels. Mutations in the solute carrier family 5 member 2 (SLC5A2) gene, which encodes sodium-glucose cotransporter 2 (SGLT2), have been reported to be responsible for the disease. Genetic testing of the SLC5A2 gene was conducted in a Chinese family with FRG. A number of online tools were used to predict the potential effect of the identified mutations on SGLT2 function. Additionally, the SLC5A2 mutations previously reported in PubMed were summarized. A novel compound heterozygous mutation (c.514T>C, p.W172R; c.1540C>T, p.P514S) of the SLC5A2 gene in a Chinese child with FRG was identified. In total, 86 mutations of the SLC5A2 gene have been reported to be associated with FRG. The novel compound heterozygous mutation (c.514T>C, p.W172R; c.1540C>T, p.P514S) of the SLC5A2 gene may be responsible for the onset of FRG. The present study provides a starting point for further investigation of the molecular pathogenesis of the SLC5A2 gene mutation in patients with FRG.