In 1963 Liddle et al.1 described a disorder that simulated primaryaldosteronism, characterized by severe hypertension and hypokalemiabut with negligible secretion of aldosterone. They theorizedthat this was "a disorder in which the renal tubules transportions with such abnormal facility that the end result simulatesthat of a mineralocorticoid excess." We describe a woman withthis syndrome (the index case1) in whom renal failure eventuallydeveloped and who received a cadaveric renal transplant at ourinstitution in 1989. Her disorder resolved after transplantation,with normalization of the aldosterone and renin responses tosalt restriction. The woman's extended pedigree demonstratesautosomal dominant inheritance of severe hypertension and suppressedaldosterone secretion, but hypokalemia is not a constant findingin the affected members of the family.
Case Report
In 1960, the proband, then 16 years of age, had hypertensionand hypokalemic metabolic alkalosis. A brother and sister, 14and 19 years old, respectively, had the same abnormalities.The fact that their urinary aldosterone excretion was low evenwhile they were eating a low-sodium diet (9 mmol per day) excludeda diagnosis of primary aldosteronism. Ingestion or hypersecretionof other mineralocorticoids was excluded by the findings ofhigh sodium:potassium ratios in saliva and sweat, a lack ofeffect of spironolactone on electrolyte excretion and hypertension,and normal urinary excretion of glucocorticoid metabolites1.
The proband's hypertension was poorly controlled, and her renalfunction deteriorated. In 1981 her creatinine clearance was41 ml per minute (0.68 ml per second); dialysis was begun inMay 1989. She underwent transplantation with a cadaveric kidneyin November 1989 and now has excellent renal function with mildhypertension and normokalemia. She is the only family memberto have had renal failure, and its cause is unknown. A biopsyperformed in 19621 revealed only a slight increase in the cellularityof several glomeruli with occasional adhesions.
Methods
For the studies described here, which were performed while shewas hospitalized in the General Clinical Research Center inJuly 1991, the woman was given a diet containing 150 mmol ofsodium per day for four days and then a sodium-restricted diet(9 mmol per day) for four days. Her potassium intake was 60mmol per day. Plasma renin activity and aldosterone concentrationswere measured after she had spent 30 minutes in a supine positionon day 4 of each diet. Electrolytes in serum and urine weremeasured daily. At the time of the study, her serum creatininelevel was 1.0 mg per deciliter (88.4 µmol per liter);sodium, 135 mmol per liter; potassium, 4.3 mmol per liter; bicarbonate,24 mmol per liter; and chloride, 108 mmol per liter. Her creatinineclearance was 77 ml per minute (1.28 ml per second). She wastaking 200 mg of cyclosporine per day, 10 mg of prednisone perday, and 100 mg of azathioprine per day at the time of study.The same tests were carried out in 20 unrelated, stable renal-transplantrecipients who were receiving prednisone and either cyclosporine(10 patients) or azathioprine (10 patients).
Blood pressure was measured in seated subjects, and overnighturinary potassium, sodium, and aldosterone excretion2 and serumelectrolyte levels were determined in the proband and 43 otherfamily members (who were seen as outpatients). No attempt wasmade to control dietary sodium intake before these measurements.Serum and urine electrolytes were measured by flame photometry,and plasma and urinary aldosterone levels and plasma renin activitywere measured by radioimmunoassay.
The studies were approved by the institutional review boardat the University of Alabama at Birmingham, and written informedconsent was obtained from each subject.
Results
In 1962, the proband's urinary sodium excretion could not bereduced maximally by sodium restriction, and she continued tohave hypertension and hypokalemia (Table 1). Liddle et al.1concluded that in this syndrome persistent volume expansionblunted any short-term stimulation of aldosterone secretionby sodium restriction. The administration of triamterene duringsalt restriction decreased urinary potassium excretion, increasedurinary sodium excretion, and corrected the hypertension andhypokalemia. There was no response to spironolactone1.
Table 1. Serial Measurements of Blood Pressure and Electrolyte Excretion in the Proband.
We studied the proband 20 months after renal transplantation.At that time, she had mild hypertension and a normal serum potassiumconcentration. Urinary sodium excretion averaged 145 mmol perday when her dietary intake was 150 mmol per day, and urinarypotassium excretion was not excessive (Table 1). Plasma reninactivity and the plasma aldosterone concentration increasednormally in response to sodium restriction, and the magnitudeof the increases was similar to that in the control transplantrecipients (Table 2). In the original report, the proband hadnegligible urinary aldosterone excretion, which did not increasewith sodium restriction1.
Table 2. Plasma Renin Activity and Plasma Aldosterone Concentrations, Measured in the Supine Position, in the Proband after Renal Transplantation and in Unrelated Renal-Transplant Recipients.
The proband's expanded pedigree is shown in Figure 1. The probandand two siblings were extensively studied in 19621. The probandhad two daughters, one of whom (Subject IV-5) was severely affectedwith Liddle's syndrome. The proband's sister, Subject III-3,had two affected children (Subjects IV-2 and IV-3), whereasboth children of Subject III-5, the proband's brother, wereunaffected. Family members whose conditions were not appropriatelydiagnosed or treated died prematurely or had cerebrovascularaccidents or cardiovascular disease (Subjects II-2, II-3, III-1,and III-13).
Figure 1. Pedigree of the Original Kindred with Liddle's Syndrome.
Subject III-4 (arrow) is the proband. The classification of family members as affected was based on the presence of hypertension, defined as a historically documented diastolic blood pressure of more than 90 mm Hg in the original report1 or the medical records, or measured by us. All the normal subjects had a ratio of urinary aldosterone (in nanograms) to potassium (in millimoles) that was more than 60, as did the proband after renal transplantation. As described in the original report,1 the proband had greatly reduced aldosterone excretion at the age of 16 years.
Hypokalemia was originally described in Subjects III-3, III-4,and III-5,1 but it was not present in all members of this familywho had hypertension. Subject III-1 had hypertension (160/100mm Hg) with normokalemia at 24 years of age and subsequentlyhad a cerebrovascular accident. Subject II-3 had borderlinehypertension (160/88 mm Hg) and a serum potassium concentrationof 3.8 mmol per liter at 35 years of age; he had two affectedchildren (Subjects III-13 and III-14).
To define this syndrome better, we studied the proband againand also studied 43 other family members as outpatients. Thesubjects were classified as affected if they had hypertension(diastolic blood pressure >90 mm Hg) or had hypertensionas compared with age-matched normal subjects. Unaffected memberswere normotensive but had an affected parent and were thereforeat risk. The control subjects, defined as those who were notat risk, included the spouses and children of unaffected familymembers.
Eighteen family members had hypertension, and as a group theirserum potassium concentrations were lower than those of the15 unaffected family members and the 10 subjects who were notat risk (Table 3). There were no significant differences betweenthe affected family members and the other two groups in theovernight creatinine clearance (Table 3) or in height; weight;sex; serum creatinine, sodium, or chloride concentrations; orurinary excretion of creatinine, sodium, potassium, or chloride(data not shown). Overnight rates of urinary aldosterone excretionand aldosterone-excretion rates normalized for potassium contentwere lower in the affected family members than in the othertwo groups (Table 3).
Table 3. Clinical Findings in a Family with Liddle's Syndrome.
Discussion
Liddle et al. proposed that high urinary potassium excretionand low urinary sodium excretion maintained hypokalemia andvolume expansion, causing hypertension and suppressing aldosteroneexcretion1. Triamterene and salt restriction corrected the hypokalemiaand hypertension, but spironolactone was ineffective, a factthat argued against an unidentified mineralocorticoid hormoneas the cause of the syndrome. Renal failure ultimately developedin the proband, and she became normokalemic. She has remainednormokalemic since receiving her renal transplant in 1989. Althoughcyclosporine can raise the serum potassium concentration andhyperkalemia can stimulate aldosterone secretion, we do notattribute the normal plasma renin and aldosterone values inthe proband after transplantation to cyclosporine, since shehad normokalemia. Furthermore, cyclosporine does not interferewith the renin and aldosterone responses to salt restriction3and to the administration of captopril4. Once she had a well-functioninggraft, the response of the proband's renin-aldosterone axisto salt restriction was normal (Table 2), despite the administrationof cyclosporine.
Other studies have confirmed the original description by Liddleet al. and have found that amiloride and triamterene, but notspironolactone, were effective treatments for hypertension andhypokalemia in patients with this syndrome as long as dietarysodium intake was restricted1,5,6,7. Chronic suppression ofaldosterone secretion is a constant finding, and renal biopsyshows atrophy of the juxtaglomerular apparatus and loss of renin-secretinggranules6. Suppression of the renin-angiotensin system is not,however, an integral feature of this disorder7; rather, it simplyreflects the chronic state of expansion of the extracellular-fluidvolume1,5.
Patients with Liddle's syndrome have an enhanced influx of sodiuminto the red cells,6,8 but there is no generalized increasein the permeability of the cell membrane to sodium, becausethe ratio of sodium to potassium in saliva and sweat is normal,1,5and fecal potassium wasting is not a problem1. The ameliorationof the syndrome by renal transplantation suggests that the disorderis not caused by an unidentified mineralocorticoid and providesevidence of a specific transport defect in the segments of thedistal nephron that regulate sodium and potassium excretionand respond to aldosterone, amiloride, and triamterene9.
The epithelial sodium channel is a multimer that includes anidentified membrane-spanning protein,10 regulatory subunits,and a G protein sensitive to pertussis toxin11,12. Constitutiveactivation of any component of this complex could cause Liddle'ssyndrome. Constitutive activation of the mineralocorticoid receptor,specifically in the collecting tubule, could also explain thesyndrome.
This pedigree (Figure 1) clearly demonstrates autosomal dominantinheritance. The male-to-male transmission between SubjectsII-3 and III-13, II-5 and III-17, III-17 and IV-18, and II-6and III-20 is evidence against X-linked inheritance. Liddleet al. reported that the proband's mother (Subject II-1) andmaternal grandmother (Subject I-1) had hypertension and diedprematurely1. We learned that the maternal grandfather (SubjectI-2) remarried and had six additional, unaffected children;this is consistent with the assumption that Subject I-1 wasthe source of the genetic abnormality in this family.
The phenotype consists of hypertension, a low rate of urinaryaldosterone excretion, and a low ratio of aldosterone to potassiumin the urine. Variation in the severity and onset of hypertensionimplies variable penetrance of the gene or genes involved. Althoughthe onset of hypertension usually occurs during the teenageyears, some affected family members (Subjects IV-14 and IV-18)were younger. The value of these measurements will be establishedonce the causal mutation is identified. There are normotensive,normokalemic family members who have low aldosterone-excretionrates and ratios of aldosterone (in nanograms) to potassium(in millimoles) below 60 (0.166 nmol of aldosterone per millimoleof potassium) (Subjects III-16, IV-4, IV-11, and IV-15), suggestingthat the primary effect of the gene may antedate overt hypertension.This finding makes it unlikely that reduced aldosterone excretionresults from hypokalemia or hypertension13,14.
Hypokalemia is not a universal finding among affected membersof this family. Three living family members (Subjects II-6,III-11, and III-13) and one described by Liddle et al.1. (SubjectIII-1) had hypertension with serum potassium concentrationsgreater than 4.0 mmol per liter. Only one of them, Subject III-11,was taking triamterene at the time of the study. Subjects III-2and II-3 had hypertension but had serum potassium concentrationsof 3.6 and 3.8 mmol per liter, respectively1. Primary aldosteronismis usually associated with hypokalemia,15 but it is less frequentamong patients with other mineralocorticoid-excess syndromes.For example, in a large kindred with glucocorticoid-remediablealdosteronism, the mean serum potassium concentration was 4.3mmol per liter in 12 affected and 18 unaffected family members16.It is unknown whether familial syndromes1,16,17 account fora substantial number of patients with low-renin hypertension.The usefulness of spontaneous hypokalemia as a sign of mineralocorticoidexcess is questionable, and direct measurements of the excretionof electrolytes and steroidal metabolites are necessary, atleast in the familial hypertensive syndromes.
Supported by a General Clinical Research Center core grant (5M01 RR00032) from the National Center for Research Resources,by a George M. O'Brien Kidney and Urologic Disease ResearchGrant (P50-DK39258) from the National Institute of Diabetesand Digestive and Kidney Diseases, and by the Department ofVeterans Affairs Research Service.
We are indebted to Drs. Arnold G. Diethelm and Guru Prakashfor their ongoing care of the proband; to James K. Bubien, Ph.D.,and Richard P. Lifton, M.D., Ph.D., for their interest and suggestions;to the physicians who helped us with the collection of datafrom family members: Judy Cheng, M.D., Carlton Clark, M.D.,Kirit K. Joshi, M.D., Frederick Koehler, M.D., Bradley Merritt,M.D., William Nolin, M.D., John Shilling, M.D., Daniel Sicca,M.D., and Ted Williams, M.D.; and to Patsy Jones, R.N., Mrs.Lee McGuire, Mrs. Juanita Baggett, and Connie Gibson, M.T. (A.S.C.P.),S.H., for their assistance.
Source Information
From the Departments of Medicine (M.B.-V., J.J.C., D.G.W.) and Physiology (D.G.W.), the General Clinical Research Center (J.J.C.), and the Nephrology Research and Training Center (M.B.-V., J.J.C., D.G.W.), University of Alabama at Birmingham, and the Veterans Affairs Medical Center (D.G.W.), both in Birmingham, Ala. Presented in preliminary form at the 25th Annual Meeting of the American Society of Nephrology, Baltimore, November 15-18, 1992 (J Am Soc Nephrol 1992;3:517a. abstract).
Address reprint requests to Dr. Warnock at the Division of Nephrology, University of Alabama at Birmingham, UAB Station, Birmingham, AL 35294-0007.
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