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renal tubular acidosis (RTA) type II (proximal RTA)

Etiology: 1) genetic forms - carbonic anhydrase-2 deficiency 2) associated conditions: a) amyloidosis b) multiple myeloma c) autoimmune disorders including: 1] Sjogren's syndrome 2] systemic lupus erythematosus d) chronic active hepatitis e) interstitial nephritis f) renal transplantation g) cystinosis h) Wilson's disease i) Fanconi syndrome with aminoaciduria, glucosuria, phosphaturia hypophosphatemia, hypouricemia may result in RTA II j) vitamin D deficiency [3] k) renal tubular proteinuria [3] 3) pharmacologic agents associated with isolated RTA-2 a) carbonic anhydrase inhibitors (acetazolamide) b) sulfanilamide c) topiramate d) ifosfamide e) tenofovir, cidofovir f) tacrolimus g) cyclosporine h) tetracycline (outdated) i) cisplatin (Fanconi syndrome) [3] 4) heavy metal toxicity - cadmium, copper, lead, mercury 5) other toxins - toluene Epidemiology: autosomal recessive form rare Pathology: - defect in proximal tubule resorption of HCO3- Genetics: 1) autosomal recessive form caused by mutation in SLC4A4 gene associated with severe renal tubular acidosis 2) autosomal dominant form 3) X-linked form ? Clinical manifestations: 1) osteopenia (not as severe as type I) 2) no nephrolithiasis 3) growth retardation, short stature 4) mental retardation 5) bilateral glaucoma 6) cataracts 7) band-keratopathy Laboratory: 1) metabolic acidosis a) urine pH: generally < 5.5 as serum HCO3- declines [3], but may be > 5.5 b) serum HCO3-: 14-20 meq/L, ~16-18 meq/L [3] c) anion gap is normal d) normal or negative urinary anion gap [3] 2) serum aldosterone normal to high 3) hypokalemia (may be normal) 4) aminoaciduria, glycosuria despite normal glucose, phosphaturia, hypophosphatemia (Fanconi syndrome) 5) normal 24 hour urine citrate Management: 1) attempt to treat the underlying cause 2) HCO3- or citrate: 5-15 meq/kg/day may be required a) citrate may cause fewer side effects than HCO3- b) HCO3- wasting occurs with HCO3- therapy [3] c) HCO3- may not correct acidosis [3] 3) K+ replacement (HCO3- administration may cause hypokalemia) - a potassium-sparing diuretic may reduce renal potassium wasting 4) thiazide diuretics a) may increase proximal tubule resorption b) inhibits Ca+2 excretion into the urine c) may induce hypovolemia reducing GFR decreasing glomerular filtration of HCO3-

General

renal tubular acidosis (RTA)

Database Correlations

OMIM 604278

References

  1. Manual of Medical Therapeutics, 28th ed, Ewald & McKenzie (eds), Little, Brown & Co, Boston, 1995
  2. Harrison's Principles of Internal Medicine, 13th ed. Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 1324
  3. Medical Knowledge Self Assessment Program (MKSAP) 15, 16, 17, 18, 19. American College of Physicians, Philadelphia 2009, 2006, 2015, 2018, 2021. - Medical Knowledge Self Assessment Program (MKSAP) 19 Board Basics. An Enhancement to MKSAP19. American College of Physicians, Philadelphia 2022
  4. Liamis G, Milionis HJ, Elisaf M. Medication-induced hypophosphatemia: a review. QJM. 2010 Jul;103(7):449-59. PMID: 20356849