Diagnosing apparent mineralocorticoid excess in a child with hypertension and nephrocalcinosis: from symptoms to genetics

Abstract

Apparent mineralocorticoid excess (AME) is a rare genetic disorder caused by reduced activity of the 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) enzyme. It is characterized by hypertension, hypokalemia, and low levels of renin and aldosterone. This study presents the case of a 2-year-old female patient who exhibited abdominal distension, hypertension, recurrent hypokalemia with metabolic alkalosis, failure to thrive, polyuria, and features of rickets. Furthermore, the patient presented with nephrocalcinosis and enlarged kidneys with a normal renal Doppler study. The genetic analysis revealed a homozygous mutation in the HSD11B2 gene, confirming the diagnosis of AME. The treatment with amiloride and spironolactone resulted in normalized urine output, stabilized blood pressure, and balanced electrolyte levels. This case emphasizes the importance of considering AME in pediatric patients presenting with unexplained refractory hypertension associated with hypokalemia and nephrocalcinosis, and it underscores the crucial role of genetic testing in diagnosis and management.

Introduction

Apparent mineralocorticoid excess (AME) is an autosomal recessive disorder characterized by the absence or dysfunction of the enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2). The diagnosis of AME is predicated on three primary clinical manifestations: hypokalemia, low plasma renin-aldosterone levels, and hypertension. This report presents a case of AME in a 2.5-year-old female patient who additionally exhibited nephrocalcinosis, renal enlargement, and features consistent with rickets.

Case report

A 2.5-year-old female, the firstborn of non-consanguineous parents, presented with a history of abdominal distension, predominantly in the upper quadrants, since 4 months of age. There was no associated history of jaundice, decreased urine output, pedal edema, or facial puffiness. However, the patient exhibited polyuria and polydipsia from the same age and had not demonstrated appropriate height and weight gain. There was no history of polyphagia, salt craving, loose stools, or skeletal deformities. The child experienced recurrent episodes of hypokalemia with hypertension, necessitating potassium supplementation along with the addition of amlodipine and labetalol for blood pressure control during previous visits to a local clinic at 8 months of age. Her antenatal and birth history were unremarkable, with a birth weight of 2.2 kg and no history of polyhydramnios or oligohydramnios. She was fully immunized and developmentally normal, with no family history of early-onset hypertension, stroke, sudden death or similar complaints.

Upon physical examination, the patient exhibited hypertension, with a blood pressure of 130/90 mmHg while receiving amlodipine at 0.4 mg/kg and labetalol at 30 mg/kg. The anthropometric measurements revealed a weight-for-age z-score of − 2.38 and a height-for-age z-score of − 2.2. The patient presented with pallor, widening of the wrists, and double malleoli. Abdominal examination demonstrated distension and a palpable liver 1 cm below the right costal margin (liver span of 10 cm), which was soft and non-tender; no palpable spleen or shifting dullness was observed on percussion. The external genitalia were normal and the remainder of the systemic examination was unremarkable. Venous blood gas analysis indicated metabolic alkalosis, hypokalemia, and hypochloremia.

Diagnosis and management

The initial considerations encompassed reno-vascular hypertension, apparent mineralocorticoid excess, Liddle syndrome, familial hyperaldosteronism and congenital adrenal hyperplasia. Initial investigations were conducted, as presented in Table 1. The patient continued on amlodipine and labetalol, and enalapril was subsequently added following a normal renal artery Doppler ultrasound. Blood pressure was subsequently controlled with amlodipine at 0.6 mg/kg, enalapril at 0.5 mg/kg, and labetalol at 40 mg/kg. Ophthalmological examination revealed grade 2 hypertensive retinopathy, while electrocardiogram and 2D echocardiogram were within normal limits. The patient exhibited polyuria, with a urine output of 8 ml/kg/h. The serum osmolality was 290 mosm/kg and urine osmolality was 107 mosm/kg. The polyuria resolved upon correction of hypokalemia. The transtubular potassium gradient (TTKG) measured during hypokalemia was 10. Abdominal ultrasound demonstrated bilateral nephromegaly (right kidney 8 cm, left kidney 8.4 cm) with medullary nephrocalcinosis and an elevated spot urine calcium-to-creatinine ratio and normal size and appearance of adrenals. Given the constellation of metabolic alkalosis, hypokalemia, hypertension, and a normal renal artery Doppler, monogenic hypertension was suspected.

Table 1.

Baseline investigations of the index patient

Investigation
Hemoglobin	9.4 g/dl
Total Leukocyte count	11,210/μl
Platelet count	4,88,000/μl
MCV/MCH/MCHC	71 fl/25 pg/cell/28 g/dl
Urea/Creatinine	12 mg/dl/0.32 mg/dl
Sodium/ Potassium/Chloride	148 meq/L/4 meq/L/108 meq/L
Protein/albumin	6.9 g/dl/4.2 g/dl
Total Bilirubin/ Direct Bilirubin	0.5 mg/dl/0.06 mg/dl
ALT/AST/ALP	35 IU/L/29 IU/L/231 IU/L
Serum Magnesium	2.8 mg/dl
Serum osmolarity	290 mosm/Kg
Urine osmolarity	107 mosm/Kg
Urine Routine microscopy	Protein negative WBC nil/hpf RBC nil/hpf
Spot urine protein creatinine ratio	0.37 (mg/mg)
Spot urine calcium creatinine ratio	1.08 (mg/mg)
Vitamin D / Intact PTH	10 ng/ml/112 pg/ml
Calcium/Phosphate	9.1 mg/dl/4.9 mg/dl
Iron/TSAT/TIBC/Ferritin	62 μ/dl/15.5%/398 μ/dl/282 ng/ml
Vitamin B12/ Folate	102 pg/ml/21 ng/ml

MCV Mean corpuscular volume, MCH Mean corpuscular hemoglobin, MCHC Mean corpuscular hemoglobin concentration, ALT Alanine transaminase, AST Aspartate transaminase, ALP Alkaline phosphatase, iPTH intact parathormone, TSAT Transferrin saturation, TIBC Total iron binding capacity

Renin and aldosterone levels could not be measured. However, a clinical exome analysis identified a homozygous novel missense variant in the HSD11B2 gene in exon 3 (c.577 T > G; p.Phe193Val), classified as a variant of unknown significance (VUS) according to ACMG guidelines, as it had not been previously reported, although the phenotype was consistent.

Multiple computational predictions suggest that this mutation is likely pathogenic, with RAVEL score and PROVEAN predicting it as “pathogenic moderate,” and SIFT and LRT classifying it as “damaging.” Additionally, the reference codon (Phenylalanine at position 193) is highly conserved across species, supporting the functional importance of this residue (Fig. 1). This variant has been submitted to ClinVar (Accession no.: SCV005199910). The parental segregation analysis revealed that the same HSD112 gene variant was present in heterozygous form in both asymptomatic parents. The patient was initiated on amiloride, titrated to a maximum dose of 0.3 mg/kg/day, and spironolactone at 3 mg/kg/day.

Fig. 1.

A. In silico prediction of the variant using multiple computational predictions, B. Individual scores of various tools and their predictions, C. Snapshot showing conserved amino acids throughout different species

Follow-up and outcome

The patient's urine output normalized, polydipsia resolved, and appetite improved. Anemia ameliorated with iron and vitamin B12 supplementation. Nutritional rehabilitation consisted of a salt-restricted, high-protein, and high-calorie diet, which resulted in weight gain. The growth of the child has been illustrated in Fig. 2. The manifestations of rickets improved following the correction of vitamin D levels and nutritional rehabilitation. The patient remained normotensive while receiving antihypertensive medication. Amiloride and spironolactone were continued and were well-tolerated, with no adverse events. The serum electrolytes remained stable during the follow-up period. Hypercalciuria improved with normalization of the urine calcium creatinine ratio after 1.5 years of treatment. Repeat abdominal ultrasound revealed normal-sized kidneys (7.5 and 7.4 cm) with nephrocalcinosis (Fig. 3). The trends in biochemical investigations with treatment have been outlined in Table 2. Genetic counseling was provided for the family.

Fig. 2.

WHO growth chart depicting the trend of height and weight of the child

Fig. 3.

Ultrasound of the kidney showing bilateral nephrocalcinosis

Table 2.

Trend of investigations of the index patient on follow-up

Age (months)	33	35	38	44	46	49	53	57	61
Blood pressure (mm of Hg)	110/76	100/70	88/60	100/62	90/60	90/60	80/56	82/60	106/62
Height (cm)	85	87.7	90.2	92.6	94.4	96.4	98.9	101	105
Weight (Kg)	10	11	11.5	12.3	13.5	13.5	14.6	16.4	16.2
Creatinine (mg/dl)	0.4	0.4	0.49	0.45	0.47	0.52	0.5	0.48	0.5
Potassium (Meq/l)	2.5	3.5	4.4	4.3	4.2	3.8	4.2	4.6	5.2
pH	7.4	7.4	7.43	7.43	7.35	7.41	7.39	7.4	7.41
Bicarbonate	32	22	27	27.9	22.8	25.6	26.4	25	24
Urine Calcium Creatinine ratio (mg/mg)	1.8			0.6					0.2
Medication
Amlodipine (mg/kg/day)	0.6	0.5	0.5	0.5	0.2	0.3	0.2	0.2	0.2
Labetalol (mg/kg/day)	40	30	20	10	–	–	–	–	–
Enalapril (mg/kg/day)	0.5	0.5	0.5	0.5	0.5	0.2	–	–	–
Amiloride (mg/kg/day)	0.3	0.3	0.3	0.3	0.3	0.3	0.3	0.3	0.3
Spironolactone (mg/kg/day)	1	3	3	3	3	3	3	3	3

Discussion

AME is caused by a mutation in the HSD112 gene, which encodes the enzyme 11β-HSD2, predominantly expressed in the collecting duct and the epithelium of the colon [1]. Two isoforms of 11β-HSD regulate the metabolism of cortisol. A complete or partial loss of activity of the 11β-HSD2 isoform results in elevated cortisol levels, which excessively stimulate mineralocorticoid receptors, leading to hypertension, metabolic alkalosis, hypokalemia, and increased sodium reabsorption [2, 3]. A complete absence of activity results in the classical form of the disease, which manifests in infancy with symptoms such as low birth weight, failure to thrive, polydipsia, polyuria, and refractory hypertension, as observed in our case [4, 5]. The milder type 2 form typically manifests later, often during adolescence or adulthood. Previous reported cases of 11β-HSD2 mutation are presented in Table 3.

Table 3.

Previous reported cases of HSD11B2 mutation with phenotype

Patient	Age/Sex	$\downarrow$ K(meq/L)	HTN	MA (Bicarb-onate – mmol/L)	PRA/PAC	$\uparrow$ Cortisol-cortisone ratio**	Location	Variant	Refer-ence
1	11y/M	2.3	175/134	38	–	27.9*	Exon 3	p.Arg208Cys	[20]
2	9y/F	2.7	130/90	33	–	8.9*	Exon 3	P.Arg186Cys	[20]
3	10y/M	2.6	170/95	31	–	33*	Exon 4	p.Asp244Asn p.Leu250Arg	[20]
4	11y/M	2.1	180/112	38	–	26.8*	Exon 4	p.Leu250Pro p.Leu251Ser	[20]
5	3y/F	2.3	140/90	30	–	32.1*	Exon 5	E356-1	[20]
6	14y/M	3.5	170/115	29	–	9	Exon 5	p.Arg337His del(Tyr338)	[20]
7	15y/F	2.8	220/160	–	–	8.9*	Exon 5	p.Arg337Cys	[20]
8	3y/M	2.8	143/86	34	–	13.8*	Exon 5	E286-1	[20]
9	13y/M	2.9	161/119	33	$\downarrow$	4.9*	Exon 4 Exon 5	p.Ala237val p.Ala328Val	[10]
10	22 m/F	2.7	160/120	33.9	$\downarrow$	42*	Exon2	Leu114del(6nt)	[16]
11	4y/M	3	140/90	–	$\downarrow$	14.5	Exon 4	p.Asp223Asn	[21]
12	21y/M	1.7	235/125	–	–	13.57*	Exon 4	p. Pro225Pro p.Tyr226Asn	[22]
13	16y/F	2.5	220/120	–	–	1.93*	Exon 5	p.Arg359Trp	[22]
14	16y/M	1.8	136/98	–	–	7.2*	Exon 4 Exon 4	p.Cys 232Tyr p.Leu 376Pro	[22]
15	1.7y/M	1.5	155/71	33	–	3.1	Exon 1	p.Arg74Gly Pro75del(1nt)	[23]
16	3.8y/M	2.5	169/101	39	–	2	Exon 3	p.Arg221Val	[23]
17	1.8y/M	2.1	148/88	28	–	3.2	Exon 5	Val322ins9nt	[23]
18	13y/M	3.4	200/100	No	$\downarrow$	4*	Exon 2 Exon 5	p.Asp 144 Val; p.Phe367del	[24]
19	2y/M	2	180/120	Yes	$\downarrow$	26*	Exon 5	p.Glu 342 fs	[24]
20	2y/M	1.4	150/80	Yes	$\downarrow$	13*	Exon 3	p.Arg213Cys	[24]
21	4 m/F	3.6	140/100	No	$\downarrow$	2.4*	Exon 3	p.Phe185Ser	[24]
22	6y/M	2.9	160/100	No	$\downarrow$	42*	Exon 5	p.Ala328Val	[24]
23	11 m/F	$\downarrow$	135/70	Yes	$\downarrow$	45*	Exon 5	p.Cys1228Thr	[19]
24	N/A						Exon 4	p.Pro227Leu	[25]
25	N/A						Exon 4	p.Thr267Arg	[25]
26	N/A						Exon 5	p.Tyr299del	[25]
27	9mon/F	3.2	$\uparrow$	31.1	$\downarrow$	20*	Exon 5	p.Glu301Argfs*56	[1]
28	17y/M	2.87	170/100	yes	$\downarrow$	–	Exon2 Exon 5	c.343_348del c.1099_1101del	[26]

^*THF + aTHF/THE indicates tetrahydrocortisol allo-tetrahydrocortisol/ tetrahydrocortisone; Normal urinary 5 $\propto$ -THF + THF/THE = 0.7–1.2

^**Normal urinary 5 $\propto$ -THF/THF ratio: 0.7–1.4;

M male, F Female, K potassium, HTN Hypertension, MA Metabolic Alkalosis, PRA Plasma Renin Activity, PAC Plasma Aldosterone Concentration, y Year, mon Month, N/A not available

The patient presented with polyuria and low urine osmolality, likely secondary to hypokalemia, which resolved upon correction of the electrolyte disturbance. A urine-concentrating defect has been documented in AME as a potential reversible manifestation of acquired nephrogenic diabetes insipidus [6, 7]. Chronic hypokalemia can result in nephrocalcinosis and renal cyst formation. It is hypothesized that chronic hypokalemia increases intrarenal ammonium ion levels, potentially causing interstitial nephritis and dystrophic nephrocalcinosis. This may elucidate the presence of enlarged kidneys with nephrocalcinosis observed in this case. While chronic hypokalemia has also been associated with renal cyst formation in patients with AME, this was not observed in the present patient [8–10]. Research on animal models shows that hypokalemia lasting 3 to 4 weeks can cause significant renal tubular injury, including vacuolation of tubular cells and hyaline substance accumulation, leading to impaired calcium reabsorption and often irreversible damage [11, 12]. In humans, the duration of hypokalemia required to induce irreversible changes in renal tubular calcium handling is less well-defined. However, clinical studies have reported that patients with chronic hypokalemia lasting for several years develop progressive renal insufficiency, interstitial fibrosis, and tubular atrophy, which are associated with impaired calcium handling. [13] While some changes in renal tubular calcium handling are irreversible, early intervention with potassium supplementation and correction of the underlying cause of hypokalemia can prevent further progression of renal damage [13, 14]. Hypercalciuria observed in our case is consistent with findings from previous reports and is likely attributable to chronic hypokalemia affecting the renal tubular handling of calcium [1, 15, 16].

Diagnosis typically involves identifying low levels of renin and aldosterone and an elevated urine cortisol-to-cortisone ratio. Furthermore, a 24-h urinary steroid metabolite profile can be conducted to assess elevated levels of cortisol and cortisone metabolites, such as tetrahydrocortisol and allo-tetrahydrocortisol. This urinary steroid profile is crucial for differentiating AME from other conditions such as Liddle syndrome, which also presents with low renin and aldosterone levels but maintains a normal urinary steroid profile. However, genetic testing would be confirmatory [4]. The absence of a significant family history, the examination revealing normal external genitalia, the lack of hypoglycemia, and the abdominal ultrasound demonstrating normal adrenal glands and internal genitalia suggest that primary hyperaldosteronism, Liddle syndrome, and congenital adrenal hyperplasia would be less likely possible diagnoses for our case.

Due to the unavailability of endocrine testing at a reasonable cost and the accessibility of genetic testing, we proceeded directly with the later in light of the classical presentation observed, secondary to financial constraints. This represents a limitation of the current case report. Nevertheless, the clinical presentation and the response to spironolactone and amiloride substantiate the diagnosis of aldosterone-mediated excess in the absence of endocrine testing. Timely diagnosis and intervention in AME are critical, as they can substantially delay the progression of renal dysfunction and mitigate end-organ damage induced by chronic hypertension. Long-term sequelae, as documented in various studies, encompass renal dysfunction as well as cardiac, neurological, ophthalmological, and other end-organ complications, including chronic kidney disease resulting from prolonged uncontrolled hypertension [17]. These adverse outcomes are particularly pronounced in cases with delayed diagnosis and treatment [18, 19].

Conclusion

This case underscores the significance of considering AME in pediatric patients presenting with refractory hypertension, hypokalemia, and associated complications such as nephrocalcinosis. The identification of a homozygous mutation in the HSD11B2 gene in our patient, in conjunction with the clinical presentation, emphasizes the critical role of genetic testing in diagnosing AME. Efficacious management with medications such as amiloride, spironolactone, and supportive care resulted in substantial clinical improvement in our patient. Prompt diagnosis and appropriate treatment are imperative to prevent the progression of renal impairment and mitigate long-term complications associated with chronic hypertension. This case reinforces the necessity for heightened awareness and timely intervention in AME to improve outcomes and prevent end-organ damage.