Inherited tubulopathies

A child who loses salt cannot hold their blood pressure, their potassium or their growth together for long, and the inherited tubulopathies are the prototypic salt-losing and potassium-shifting disorders of childhood. Each maps onto one segment of the nephron, and each segment has a characteristic transporter whose inherited failure produces a predictable biochemistry. Bartter is the thick ascending limb defect, the loop-diuretic equivalent, with hypercalciuria and nephrocalcinosis. Gitelman is the distal convoluted tubule defect, the thiazide equivalent, with hypocalciuria and hypomagnesaemia. Liddle is the collecting duct epithelial sodium channel gone into overdrive, and it is the one that raises the blood pressure. Fanconi is different in kind, a wholesale failure of the proximal tubule that loses glucose, phosphate, amino acids and bicarbonate and causes a metabolic acidosis rather than an alkalosis. [5] [6]

The bedside power of the topic comes from two branching questions. First, is the blood pressure high or normal and low, because a hypokalaemic alkalosis with hypertension points straight to Liddle while the same biochemistry with a normal or low blood pressure points to Bartter or Gitelman. Second, where do the renin and aldosterone sit, because Liddle suppresses both, primary hyperaldosteronism raises the aldosterone but not the renin, and Bartter and Gitelman raise both. Nail this two-step branch and you have answered the spine of every tubulopathy viva before you reach the genes. [7] [10]

Overview & Definition

An inherited tubulopathy is a monogenic disorder in which a single transporter or channel along the nephron fails, producing a predictable pattern of electrolyte and fluid loss. The defining biochemistry is determined by which segment broke. The salt-losing syndromes, Bartter and Gitelman, and the sodium-retaining syndrome, Liddle, all produce a hypokalaemic metabolic alkalosis. Fanconi syndrome stands apart, because a generalised proximal tubular failure wastes bicarbonate and produces a normal anion gap metabolic acidosis with glycosuria, phosphaturia and aminoaciduria. [5] [6]

The four syndromes are best held against the segment of nephron each one breaks. Bartter syndrome is the inherited failure of salt reabsorption in the thick ascending limb of the loop of Henle, and it mimics a loop diuretic given for life. Gitelman syndrome is the failure of the thiazide-sensitive sodium chloride cotransporter in the distal convoluted tubule, and it mimics a thiazide diuretic. Liddle syndrome is a gain-of-function of the epithelial sodium channel in the collecting duct, so the kidney retains sodium and loses potassium without any aldosterone driving it. Fanconi syndrome is a diffuse failure of proximal tubular reabsorption, so everything the proximal tubule normally reclaims, glucose, phosphate, amino acids and bicarbonate, is spilled into the urine. [3] [4]

What unifies the topic clinically is that all four present in childhood with electrolyte disturbance and growth failure, and that each has a treatment aimed at the segment that broke. The magnesium and potassium-sparing diuretic strategy suits Gitelman, the prostaglandin synthesis inhibitor strategy suits antenatal Bartter, the amiloride strategy suits Liddle, and the bicarbonate, phosphate and cause-specific strategy suits Fanconi. The examiner rewards the candidate who can move fluently from the bedside biochemistry to the segment, the gene and the treatment, and that fluency is what this page builds. [1] [2]

References12Show ledgerHide ledger

1. [1]Konrad M, et al Diagnosis and management of Bartter syndrome: executive summary of the consensus and recommendations from the European Rare Kidney Disease Reference Network Working Group for Tubular Disorders. Kidney Int, 2021.PMID 33509356
2. [2]Blanchard A, et al Gitelman syndrome: consensus and guidance from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference. Kidney Int, 2017.PMID 28003083
3. [3]Fulchiero R, et al Bartter Syndrome and Gitelman Syndrome. Pediatr Clin North Am, 2019.PMID 30454738
4. [4]Foreman JW Fanconi Syndrome. Pediatr Clin North Am, 2019.PMID 30454741
5. [5]Kleta R, et al Salt-Losing Tubulopathies in Children: What's New, What's Controversial? J Am Soc Nephrol, 2018.PMID 29237739
6. [6]Iancu D, et al Inherited Renal Tubulopathies-Challenges and Controversies. Genes (Basel), 2020.PMID 32150856
7. [7]Kermond R, et al A clinical approach to tubulopathies in children and young adults. Pediatr Nephrol, 2023.PMID 35585366
8. [8]Do C, et al Metabolic Alkalosis Pathogenesis, Diagnosis, and Treatment: Core Curriculum 2022. Am J Kidney Dis, 2022.PMID 35525634
9. [9]Tetti M, et al Liddle Syndrome: Review of the Literature and Description of a New Case. Int J Mol Sci, 2018.PMID 29534496
10. [10]Athimulam S, et al Low-Renin Hypertension. Endocrinol Metab Clin North Am, 2019.PMID 31655771
11. [11]Albuquerque ALB, et al Inherited Fanconi syndrome. World J Pediatr, 2023.PMID 36729281
12. [12]Elmonem MA, et al Cystinosis: a review. Orphanet J Rare Dis, 2016.PMID 27102039