Pregnancy-Associated Polyuria in Familial Renal Glycosuria

Case Report Pregnancy-Associated Polyuria in Familial Renal Glycosuria Hakan R. Toka, MD, PhD,1,2 Jun Yang, MD,2 Chloe A. Zera, MD,3 Jeremy S. Duffield, MD, PhD,4 Martin R. Pollak, MD,1 and David B. Mount, MD, FRCPC2,5 A pregnant woman presented at gestational week 28 with loss of consciousness and profound polyuria. Further characterization revealed osmotic diuresis due to massive glycosuria without hyperglycemia. Glycosuria reduced substantially postpartum, from ⬃100 to ⬃30 g/1.73 m2 per day. DNA sequencing analysis of the SLC5A2 gene encoding the renal glucose transporter SGLT2 showed a homozygous frame-shift mutation (occurring after the glutamine at amino acid 168 and leading to premature termination of the protein at amino acid 186) diagnostic of familial renal glycosuria. Pregnant women with familial renal glycosuria can be at risk of profound polyuria during pregnancy due to the associated increase in glycosuria. These findings also have implications for the use of SGLT2 inhibitors in clinical practice. Am J Kidney Dis. xx(x):xxx. Published by Elsevier Inc. on behalf of the National Kidney Foundation, Inc. This is a US Government Work. There are no restrictions on its use. INDEX WORDS: Familial renal glycosuria; polyuria; natriuresis; vasopressin; SGLT2, SCL5A2.

P

olyuria is caused by either water or solute diuresis.1 Pregnancy-associated water diuresis has several causes, including gestational diabetes insipidus.2 Water homeostasis undergoes dramatic modulation during pregnancy. Pregnancy thus is associated with a reduction in the osmotic threshold for central arginine vasopressin (AVP) release, with a progressive increase in AVP degradation mediated by circulating placental vasopressinase.3,4 Gestational diabetes insipidus occurs when a relative excess of vasopressinase leads to a decrease in circulating AVP and water diuresis.2 Gestational diabetes mellitus (DM), in contrast, causes a solute diuresis. We report a nondiabetic patient with profound pregnancy-associated polyuria due to massive glycosuria from familial renal glycosuria.

CASE REPORT A 30-year-old gravida 2 para 1 at 28 weeks’ gestation developed witnessed loss of consciousness. Physical examination revealed no abnormalities of mother or fetus. Her initial blood pressure was 96/50 mm Hg with a heart rate of 102 beats/min. Ultrasonography and chest computed tomography findings were negative for thromboembolic events. Brain imaging and electroencephalography findings were normal. The patient reported that her vision had gone “suddenly black” and that she had experienced similar episodes during her prior pregnancy, which was notable for glycosuria without DM. The patient’s laboratory data are listed in Tables 1 and 2. She exhibited profound polyuria. She had noticed the abrupt onset of nocturia at 26 weeks. Laboratory data showed solute diuresis from glycosuria and natriuresis. An oral glucose tolerance test result was not consistent with gestational DM, but indicated glucose intolerance. There was generalized aminoaciduria, without phosphaturia or uricosuria. The patient was initiated on a diabetic diet. A clinical diagnosis was made of familial renal glycosuria,5 which is caused by mutations in the SLC5A2 (solute carrier family 5 member 2) gene. Fourteen sets of primer pairs for SLC5A2,6 with a more inclusive Am J Kidney Dis. 2013;xx(x):xxx

reverse primer for exon 8, were used for polymerase chain reaction amplification of genomic DNA followed by bidirectional sequencing. This revealed a homozygous single-nucleotide deletion in exon 5, the cytosine at position 506 of the coding sequence, causing a frame shift occurring after the glutamine at amino acid 168, with premature truncation of the protein at amino acid 186. A heterozygous carrier of this particular mutation has been reported previously, exhibiting severe glycosuria compared with heterozygotes for other mutations.7 DNA from the patient’s older son was sequenced, showing that he was heterozygous for the mutation (Fig 1A). Given the patient’s homozygosity for this rare mutation, her family history was revisited; she reported that her parents are first cousins. The patient underwent a 4-hour water deprivation test that failed to increase urine osmolality (Table 3). Serum AVP levels remained undetectable during the test, with no urinary response to intravenous desmopressin acetate (DDAVP). She was maintained on oral DDAVP treatment until delivery (see Discussion). Due to orthostatic symptoms at 29 weeks, with an increase in renin and aldosterone levels, she also was started on oral salt tablets. Her urine output decreased to 2-3 L/d and she delivered a healthy male infant after induction of labor at term. Her glycosuria decreased postpartum.

From the 1Division of Nephrology, Beth Israel Deaconess Medical Center; Divisions of 2Nephrology and 3Obstetrics, Brigham and Women’s Hospital, Boston, MA; 4Division of Nephrology and Lung Biology, University of Washington, Seattle, WA; and 5Division of Nephrology, VA Boston Healthcare System, Boston, MA. Received January 10, 2013. Accepted in revised form May 15, 2013. Address correspondence to David B. Mount, MD, FRCPC, VA Boston Healthcare System, Boston, MA 02132. E-mail: david. [email protected] Published by Elsevier Inc. on behalf of the National Kidney Foundation, Inc. This is a US Government Work. There are no restrictions on its use. 0272-6386/$0.00 http://dx.doi.org/10.1053/j.ajkd.2013.05.018 1

Toka et al Table 1. Laboratory Data Parameter

28 Weeks’ Gestation

3 mo Postpregnancy

Reference Range

WBC count (⫻103/␮L) Hemoglobin (g/dL) Hematocrit (%) Platelets (⫻103/␮L) Sodium (mmol/L) Chloride (mmol/L) Potassium (mmol/L) Bicarbonate (mmol/L) SUN (mg/dL) Creatinine (mg/dL) Glucose (mg/dL) Calcium (mg/dL) Magnesium (mg/dL) Phosphate (mmol/L) Albumin (g/dL) Osmolality (mOsm/kg) Uric acid (mg/dL) Hemoglobin A1c (%) TSH (mlU/L) Aldosterone (ng/dL) Renin (ng/mL/h) AVP (pg/mL) Urine specific gravity Urine pH Urine protein Urine glucose Urine bilirubin Urine urobilirubin Urine ketones Glucose tolerance test Fasting glucose level (mg/dL) Glucose level at 1 h (mg/dL) Glucose level at 2 h (mg/dL) Glucose level at 3 h (mg/dL)

7.7 11.8 35.2 231 136 107 3.3 21 6 0.6 74 8.6 1.8 3.7 3.4 287 5.1 5.1 1.0 28; 100 (29 wk) 8.8; 10.6 (29 wk) ⬍0.5 1.025 6.0 Undetectable 3⫹ Undetectable Undetectable Undetectable

9.2 12.4 36.6 187 141 105 3.8 27 15 0.73 61 9.6 2.2 3.3 4.7 293 Not tested Not tested Not tested 5.1 2.1 17 1.023 5.5 Undetectable 3⫹ Undetectable Undetectable Undetectable

4-10 11.5-16.4 36-48 150-450 130-135a; 136-145 98-107 3.4-5 22-31 6-23 0.5-1.2 70-100 98-107 1.8-2.5 2.4-5 3.7-5.4 268-280a; 278-297 1.8-6.7 4.2-5.8 0.5-5 4-31 0.2-1.6 0-4.7 1.003-1.035 4.5-8 Undetectable Undetectable Undetectable Undetectable Undetectable

90 169 166 90

Not tested Not tested Not tested Not tested

54-94 54-179 54-154 54-139

Note: Conversion factors for units: SUN in mg/dL to mmol/L, ⫻0.357; creatinine in mg/dL to ␮mol/L, ⫻88.4; glucose in mg/dL to mmol/L, ⫻0.0551; calcium in mg/dL to mmol/L, ⫻0.2495; phosphate in mmol/L to mg/dL, ⫻3.097; uric acid in mg/dL to ␮mol/L, ⫻59.48; aldosterone in ng/dL to nmol/L, ⫻0.02774; glucose in mg/dL to mmol/L, ⫻0.05551. Abbreviations: AVP, arginine vasopressin; SUN, serum urea nitrogen; TSH, thyroid-stimulating hormone; WBC, white blood cell. a Pregnancy-associated normal values.

DISCUSSION This report describes pregnancy-associated polyuria in a woman with familial renal glycosuria, who presented with massive solute diuresis.1 The diagnosis was established by mutational analysis of the SCL5A2 gene, which encodes the renal glucose transporter SGLT2.5 Although pregnancy is known to increase glucose excretion in familial renal glycosuria,5 to our knowledge this is the first detailed characterization of an affected patient with pregnancyassociated polyuria. The human kidney reabsorbs nearly 100% (⬃140 g/d) of glucose from the glomerular filtrate. In the 2

early proximal tubule,8 apical SGLT2 proteins reabsorb glucose via sodium-dependent glucose cotransport; the homologous transporter SGLT1 mediates reabsorption in the late proximal tubule9 (Fig 1B). Classically, SGLT2 is “low affinity, high capacity” transporter, with SGLT1 the “high affinity, low capacity” transporter.10 The 2 transporters do not differ in substrate affinities, however, do differ in coupling ratios; SGLT1 transports 2 sodium ions per glucose whereas SGLT2 transports only 1 sodium. This coupling ratio endows SGLT1 with greater concentrative ability, such that it plays a significant quantitative role in renal glucose absorption.10 SGLT2-knockout mice Am J Kidney Dis. 2013;xx(x):xxx

Familial Renal Glycosuria in Pregnancy Table 2. Twenty-Four–Hour Urine Collections Pregnancy (gestational wk)

BP (mm Hg) Pulse (beats/min) Weight (lb) Volume (mL) Glucose (g/1.73 m2) Osmolality (mOsm/kg) Sodium (mmol/d) RTG (mg/dL) Creatinine (mg) CCr (mL/min) Urate (mg) Phosphate (mg)

Postpartum

28

29

30

37

40

ⴙ3 mo

ⴙ1.5 y

106/70 100 149 6,850 100 366 390 — — — — —

101/62 — 151.5 4,150 57 404 278 43 1,083 156 726 598

98/65 102 152.2 3,950 80 420 190 44 1,422 197 — —

106/67 — 157.4 2,950 — 434 171 — 1,165 — — —

117/76 — 155.8 4,225 58 365 270 — — — — —

99/68 73 137 2,300 31 526 — 59 1,446 137 667 —

104/73 81 131 1,900 35 — 167 — 932 104 509 480

Note: CCr calculated using the following formula: Urine Cr ⫻ Urine volume/(Serum Cr ⫻ time min). The threshold for RTG also was calculated, as serum glucose ⫺ [(Urine glucose ⫻ Serum Cr)/Urine Cr]. Reference ranges for urate and phosphate are 0-800 mg and 500-1,200 mg, respectively. Conversion factor for glucose in mg/dL to mmol/L, ⫻0.05551. Abbreviations: BP, blood pressure; CCr, creatinine clearance; Cr, creatinine; RTG, renal threshold for glucose (excretion).

thus reabsorb approximately one-third of filtered glucose,11 indicating a substantial reabsorptive contribution from SGLT1.9 The incomplete inhibition of renal tubular glucose reabsorption by SGLT2 inhibitors12,13 A

also is consistent with significant SGLT1-dependent glucose reabsorption. Multiple mutations in the SCL5A2 gene have been associated with familial renal glycosuria.5 The excreB

wildtype

Proximal Tubule

apical

2 K+

SGLT2

ATP

1 Na+ Gluc

patient

Gluc Glut2

S1 / S2

son

SLC5A mutation or SGLT2 inhibition

2 K+

SGLT1

ATP

2 Na+ Gluc S3

AA 168 169 170 171 ……184 185 186… …. CAG GCT CTG GGC …. ATC ACC ATG.. ….. Gln Ala Leu Gly …….Ile Thr Met…

Glycosuria

3 Na+

3 Na+ Gluc Glut1

basolateral

….CAG GTC TGG GCT .….TCA CCA TGA ….. Gln Val Trp Ala ……Ser Pro STOP

Figure 1. (A) DNA sequencing of SLC5A2 shows deletion of a single cytosine nucleotide in the patient and her son. The effect on the amino acid (AA) sequence is shown in the box below. AA 169 (alanine) is encoded by codon GCT. In our patient, a single homozygous base pair deletion in this codon causes a frame shift leading to a stop codon at AA residue 186. The patient’s son is heterozygous for the deletion, leading to overlapping DNA sequences of exon 5 after the mutation. (B) Schematic illustration of renal glucose (gluc) reabsorption across the proximal tubule. The sodium (Na⫹)/glucose cotransporter SGLT2 mediates apical uptake of glucose in proximal tubule segments S1 and S2, whereas SGLT1 is expressed in S3 segments. SGLT1 and SGLT2 differ in Na⫹:glucose coupling ratios. Intracellular glucose leaves proximal tubule cells via the basolateral glucose transporters GLUT 1 and 2. Abbreviation: ATP, adenosine triphosphate. Am J Kidney Dis. 2013;xx(x):xxx

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Toka et al Table 3. Water Deprivation Test

At start Hour 1 Hour 2 Hour 3 Hour 4 Hour 5 Hour 6 Hour 7 Hour 8

Weight (lb)

Serum Sodium (mmol/L)

Serum Osmolality (mOsm/kg)

Urine Osmolality (mOsm/kg)

AVP (pg/mL)

148 147.5 147 147 146.25

138 139 142 140 141 139 137 139 140

286 293 297 — — — — — —

426 452 485 533 492 475 500 471 411

0.7 — 1.0 0.7 ⬍0.5 — 0.5 0.5 ⬍0.5

Note: The patient underwent a 4-hour water deprivation test at 28 gestational weeks. At time “0,” serum chemistry, serum osmolality, and AVP levels were obtained on ice and repeated every hour of the test. After 4 hours, the patient received 1 dose of 2 ␮g of DDAVP intravenously. Reference range for AVP is 0-4.7 pg/mL. Abbreviations: AVP, arginine vasopressin; DDAVP, desmopressin acetate.

tion of glucose only rarely approaches the filtered load in familial renal glycosuria, even in patients with a predicted complete loss of SGLT2 function.5 Again, this is consistent with residual mechanisms for glucose reabsorption. The generalized aminoaciduria observed here has been reported previously in familial renal glycosuria14 and pregnancy.15 The patient’s antepartum glucose excretion was approximately 3 times higher than postpartum. Notably, pregnancy-associated glycosuria in the absence of DM is well described, occurring in as much as 6% of pregnancies16 and reaching up to 10-20 g/d of glucose.17 Glucose titration studies indicate a significant reduction in the tubular maximum of reabsorption, consistent with acquired inhibition.18 In this patient with familial renal glycosuria, the antepartum renal threshold for glucose was lower; it is conceivable but speculative that pregnancy caused inhibition of residual SGLT2-independent glucose reabsorption, leading to glucose excretion that more closely approached the filtered load. The patient’s antepartum creatinine clearance was significantly higher than her postpartum creatinine clearance; this glomerular hyperfiltration likely was a significant factor in her glycosuria, by increasing the filtered load of glucose. This also explains the onset of her symptoms at the beginning of the third trimester, when hyperfiltration becomes maximal.19 Additionally, we hypothesize that pregnancy-associated insulin resistance caused an increase in glucose production, further augmenting the filtered load. Normal pregnancy is associated with a 50% decrease in insulin-mediated glucose disposal, inducing a 200%-250% increase in insulin secretion to maintain euglycemia; women with underlying insulin resistance develop gestational DM.20 Our patient did not meet criteria for gestational DM. However, her oral glucose tolerance test indicated impaired glucose tolerance, with 1- and 2-hour glucose values ⬎160 mg/dL. This is particularly significant in the 4

setting of familial renal glycosuria, given that SLGT2 inhibitors improve oral glucose tolerance test results in type 2 DM.12 The patient also had a substantial, sustained natriuresis. Osmotic diuresis due to glucose is associated with an obligatory natriuresis of 50-70 mEq/L.21 At gestational week 29, serum aldosterone and plasma renin activity were increased compared to week 28, albeit only slightly higher than the normal ranges in the third trimester.22 Orthostatic symptoms improved with salt supplementation. Although sodium excretion has not been detailed in patients with familial renal glycosuria, activation of the renin-angiotensin-aldosterone system has been reported in patients with severe glycosuria.5 The abrupt onset of polyuria in the third trimester, with undetectable AVP and elevated serum sodium levels for pregnancy, suggested gestational diabetes insipidus. Serum AVP levels did not increase with water deprivation. However, notably, AVP assays during pregnancy should include o-phenanthroline, an inhibitor of vasopressinase,23 to prevent in vitro proteolysis of AVP; the presence of this inhibitor is not validated for the AVP assay used. The absence of a significant acute and long-term response of urinary osmolality to DDAVP suggests that the patient did not have gestational diabetes insipidus; however, increased urinary solutes can blunt the response to AVP.21,24 We elected to continue therapy with oral DDAVP until delivery given the progressive increase in third-term vasopressinase levels,3 the induction of AVP during diabetic glycosuric states,25 the antinatriuretic activity of DDAVP,26 the fetal consequences of profound polyuria,27 and the blunting of the AVP response to hypertonicity in late-term pregnancy.4 Ultimately, gestational diabetes insipidus was not believed to have contributed to the polyuria given the decrease in postpartum osmolar excretion (⬃2,600 vs ⬃1,200 mOsm/d) indicative of profound solute diuresis. Am J Kidney Dis. 2013;xx(x):xxx

Familial Renal Glycosuria in Pregnancy

Key principles highlighted by this case include the potential for pregnancy to exacerbate or cause glycosuria in familial renal glycosuria and other nondiabetic patients,17 respectively; the potential for variable glycosuria and polyuria in familial renal glycosuria and by extension during SGLT2 inhibition; the renal resistance to AVP with increased urinary solutes21,24; and the obligate natriuresis induced by glycosuria.21 SGLT2 inhibitors, recently approved for type 2 DM, cause substantial dose-dependent glycosuria.12 It is conceivable that dynamic changes in carbohydrate intake and/or glucose tolerance in patients with type 2 DM treated with SGLT2 inhibitors will transiently lead to increased glycosuria, increased natriuresis, activation of the reninangiotensin-aldosterone system, and hemodynamic or renal compromise. The risk of morbidity could be magnified in patients who are coadministered diuretics and/or renin-angiotensin-aldosterone system inhibitors, with a greater potential for acute renal insufficiency. In this respect, acute renal insufficiency has already been reported in one such patient, 11 days after starting dapagliflozin treatment.28

ACKNOWLEDGEMENTS We thank Jacob M. Koshy and Salvatore DiBartolo III for excellent technical assistance with DNA extraction and sequencing analysis of SLC5A2. Support: Grant 1P01DK070756 from the National Institute of Diabetes and Digestive and Kidney Diseases (Drs Pollak and Mount). Financial Disclosure: The authors declare that they have no relevant financial interests.

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