✅ Model Answer:
• Diagnosis: Antenatal Bartter syndrome (type I – NKCC2 or type II – ROMK).
• Evidence: Polyhydramnios, premature delivery, severe salt wasting, hypokalemic alkalosis, hypercalciuria (Ca:Cr 0.5), nephrocalcinosis, normal BP.
• Next step: Genetic testing (SLC12A1, KCNJ1). Start aggressive electrolyte replacement (potassium chloride 4-6 mEq/kg/day, sodium chloride, magnesium), indomethacin (1-2 mg/kg/day) to reduce prostaglandin-mediated salt wasting. Monitor electrolytes, growth, and renal function.

✅ Model Answer:
• Type I: SLC12A1 (NKCC2 – Na-K-2Cl cotransporter) – accounts for ~60% of antenatal Bartter.
• Type II: KCNJ1 (ROMK – renal outer medullary potassium channel) – accounts for ~20%.
• Inheritance: Autosomal recessive (both types).
• Pathophysiology: Loss-of-function mutations in NKCC2 or ROMK impair salt reabsorption in the thick ascending limb of Henle's loop → salt wasting, volume contraction, secondary hyperaldosteronism → hypokalemic metabolic alkalosis. Increased prostaglandin E2 production worsens salt wasting. Hypercalciuria and nephrocalcinosis occur due to impaired calcium reabsorption (passive paracellular pathway).
• Polyhydramnios: Due to fetal polyuria (salt wasting leads to increased urine output in utero).
• Prematurity: Common due to polyhydramnios.

✅ Model Answer:
• Antenatal:
- Polyhydramnios.
- Premature delivery (often before 34 weeks).
• Neonatal:
- Severe salt wasting: Dehydration, poor feeding, vomiting, failure to thrive.
- Hypokalemic metabolic alkalosis (K <3.0, HCO3 >30).
- Hypercalciuria (Ca:Cr >0.2) → nephrocalcinosis.
- Polyuria, polydipsia.
- Normal blood pressure.
- Growth failure.
• Type II (ROMK): May have transient hyperkalemia in the neonatal period (due to impaired K secretion) before hypokalemia develops.
• Type I: More severe salt wasting than type II.

✅ Model Answer:
• Biochemical:
- Serum K: Low (<3.0 mEq/L).
- Serum Na: Normal or low.
- HCO3: Elevated (metabolic alkalosis).
- Serum Cl: Low (hypochloremia).
- Serum Ca: Normal.
- Urine Ca:Cr: >0.2 (hypercalciuria).
- Plasma renin and aldosterone: Elevated.
- Urine Cl: >20 mEq/L (salt wasting).
• Imaging: Renal ultrasound – nephrocalcinosis (medullary), renal stones.
• Prenatal ultrasound: Polyhydramnios.
• Genetic testing: SLC12A1, KCNJ1 (confirmatory).
• Differential: Distinguish from other Bartter types, Gitelman, and PHA1.

✅ Model Answer:
• Electrolyte replacement:
- Oral potassium chloride: 4-6 mEq/kg/day (higher doses may be needed).
- Magnesium supplementation: If hypomagnesemia is present.
- Sodium chloride: May be needed in severe salt wasting (1-2 mEq/kg/day, up to 10-20 mEq/kg/day).
• Prostaglandin synthetase inhibitors (indomethacin):
- Dose: 1-2 mg/kg/day (divided q12h).
- Mechanism: Reduces prostaglandin E2-mediated salt wasting and improves growth.
- Monitor: Renal function (creatinine), GI side effects (ulcers, bleeding).
• Nutritional support: Calorie supplementation to promote growth.
• Avoid: NSAIDs in patients with renal impairment.
• Monitor: Electrolytes, growth, renal function, and nephrocalcinosis.

✅ Model Answer:
• Growth failure: Poor weight gain, short stature.
• Nephrocalcinosis: Calcium deposition in the renal medulla → can lead to CKD.
• Nephrolithiasis: Renal stones (calcium oxalate/phosphate).
• Chronic kidney disease (CKD): Progressive renal impairment (especially with NSAID use and nephrocalcinosis).
• Hypokalemia: Muscle weakness, cramps, arrhythmias.
• Dehydration: Recurrent, severe, especially in infancy.
• Polyuria/polydipsia: Nephrogenic diabetes insipidus-like presentation.
• Prematurity-related complications: Respiratory distress, intraventricular hemorrhage, etc.

✅ Model Answer:
• Prognosis:
- Variable: Depends on the genetic subtype and severity.
- Type I (NKCC2): More severe; often requires intensive electrolyte and fluid management.
- Type II (ROMK): May have a milder course.
- Growth: Can improve with indomethacin and electrolyte replacement.
- Renal function: May decline over time (nephrocalcinosis, NSAID nephrotoxicity).
- Quality of life: Good with multidisciplinary care.
• Long-term follow-up:
- Monitor electrolytes, BP, renal function.
- Monitor growth and nutrition.
- Monitor for nephrocalcinosis (renal ultrasound).
- Avoid NSAIDs in renal impairment.
- Genetic counseling.

✅ Model Answer:
• Antenatal Bartter (type I/II):
- Gene: NKCC2 (type I) or ROMK (type II).
- Age of onset: Antenatal (polyhydramnios, prematurity).
- Salt wasting: Severe.
- Nephrocalcinosis: Common.
- Hypercalciuria: Present.
- Growth failure: Severe.
- Treatment: K, Mg, Na, indomethacin.
• Classic Bartter (type III – ClC-Kb):
- Gene: CLCNKB.
- Age of onset: Childhood (later).
- Salt wasting: Milder.
- Nephrocalcinosis: Less common.
- Hypercalciuria: Mild.
- Growth failure: Milder.
- Treatment: K, Mg, indomethacin (less often).
• Key differences: Antenatal Bartter presents with polyhydramnios, prematurity, and severe salt wasting; classic Bartter presents in childhood with milder symptoms.