From the Guidelines
Renal magnesium wasting in the context of a family history and chronic hypomagnesemia is a condition where the kidneys fail to properly reabsorb magnesium, leading to excessive urinary magnesium excretion despite low blood magnesium levels. This condition is likely to represent a hereditary renal magnesium disorder. Patients typically present with persistent hypomagnesemia, normal urinary output, and inappropriately high urinary magnesium excretion. Several genetic disorders can cause this condition, including Gitelman syndrome, Bartter syndrome, and mutations in genes encoding magnesium transporters like TRPM6 1.
Key Characteristics
- Persistent hypomagnesemia
- Normal urinary output
- Inappropriately high urinary magnesium excretion
- Family history of renal magnesium wasting
Management
- Lifelong oral magnesium supplementation, typically magnesium oxide (400-800 mg 2-4 times daily) or magnesium chloride (64-200 mg elemental magnesium 2-4 times daily), adjusted based on serum levels and symptom control
- Severe cases may require periodic intravenous magnesium sulfate
- Patients should be monitored for symptoms like muscle cramps, seizures, cardiac arrhythmias, and tetany
- Dietary adjustments to increase magnesium-rich foods (nuts, whole grains, leafy vegetables) can complement supplementation
Underlying Pathophysiology
The underlying pathophysiology involves defective magnesium transport proteins in the renal tubules, particularly in the thick ascending limb of Henle's loop or distal convoluted tubule, where most magnesium reabsorption occurs. Diuretics can also cause the depletion of important cations (potassium and magnesium), which can predispose patients to serious cardiac arrhythmias, particularly in the presence of digitalis therapy 1.
Genetic Counseling
Genetic counseling is recommended for affected families to understand inheritance patterns and risks to offspring. This can help identify individuals who may be at risk of developing renal magnesium wasting and allow for early intervention and management.
From the Research
Definition of Renal Magnesium Wasting
Renal magnesium wasting refers to the excessive loss of magnesium in the urine due to impaired renal reabsorption or increased renal excretion of magnesium [(2,3)]. This can be caused by genetic or acquired renal disorders, certain medications such as loop diuretics, or other factors [(2,3)].
Causes of Renal Magnesium Wasting
Some of the causes of renal magnesium wasting include:
- Genetic disorders such as Barter syndrome and Gitelman syndrome 2
- Use of certain medications such as loop diuretics and thiazide diuretics [(2,4)]
- Familial renal magnesium wasting, which is associated with hypercalciuria, nephrocalcinosis, and nephrolithiasis 2
- Primary hypomagnesemia with secondary hypocalcemia, a rare autosomal recessive disorder characterized by impaired intestinal absorption of magnesium and renal magnesium wasting 5
Diagnosis of Renal Magnesium Wasting
The diagnosis of renal magnesium wasting can be made by measuring the fractional excretion of magnesium and urinary calcium-creatinine ratio 2. A fractional excretion of magnesium above 2% in a subject with normal kidney function indicates renal magnesium wasting 2.
Treatment of Renal Magnesium Wasting
Treatment of renal magnesium wasting typically involves oral magnesium supplements [(2,6)]. In some cases, parenteral magnesium may be necessary for symptomatic patients with severe magnesium deficiency [(2,3)]. The potassium-sparing diuretic amiloride has also been shown to be effective in treating idiopathic renal magnesium wasting [(6,4)].