Gitelman syndrome
What is it?
Gitelman syndrome is an autosomal recessive kidney tubule disorder characterized by low blood levels of potassium and magnesium, decreased excretion of calcium in the urine, and elevated blood pH. The disorder is caused by disease-causing variants in both alleles of the SLC12A3 gene. The SLC12A3 gene encodes the thiazide-sensitive sodium-chloride cotransporter (also known as NCC, NCCT, or TSC), which can be found in the distal convoluted tubule of the kidney. The distal convoluted tubule of the kidney plays an important homeostatic role in sodium and chloride absorption as well as of the reabsorption of magnesium and calcium.
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Additional names
This group contains additional names:
- GS
Signs & symptoms
Affected individuals may not have symptoms in some cases. Symptomatic individuals present with symptoms identical to those of patients who are on thiazide diuretics, given that the affected transporter is the exact target of thiazides.
Clinical signs of Gitelman syndrome include a high blood pH in combination with low levels of chloride, potassium, and magnesium in the blood and decreased calcium excretion in the urine. Individuals affected by Gitelman syndrome often complain of severe muscle cramps or weakness, numbness, thirst, waking up at night to urinate, salt cravings, abnormal sensations, chondrocalcinosis, or weakness expressed as extreme fatigue or irritability. Though cravings for salt are most common and severe, cravings for sour foods (e.g. vinegar, lemons, and sour figs) have been noted in some persons affected. More severe symptoms such as seizures, tetany, and paralysis have been reported. Abnormal heart rhythms and a prolonged QT interval can be detected on electrocardiogram and cases of sudden cardiac death have been reported due to low potassium levels. Quality of life is decreased in Gitelman syndrome
Diagnosis
Diagnosis of Gitelman syndrome can be confirmed after eliminating other common pathological sources of hypokalemia and metabolic alkalosis. A complete metabolic panel (CMP) or basic metabolic panel (BMP) can be used to evaluate serum electrolyte levels. Renin and aldosterone can be tested in the blood. Electrolyte measurement and aldosterone levels can be done via urine. The pathognomonic clinical markers include low serum levels of potassium, sodium, chloride, and magnesium in the blood as a result of urinary excretion. Urinary fractional excretion potassium is high or inappropriately normal in the context of hypokalaemia, and high levels of urinary sodium and chloride are observed. Other clinical indicators include elevated serum renin and aldosterone in the bloodstream, and metabolic alkalosis. The symptomatic features of this syndrome are highly variable ranging from asymptomatic to mild manifestations (weakness, cramps) to severe symptoms (tetany, paralysis, rhabdomyolysis). Symptom severity is multi-factorial, with phenotypic expression varying amongst individuals within the same family. Genetic testing is another measure of identifying the underlying mutations which cause the pathologic symptoms of the disease. This mode of testing is available at select laboratories.
Treatment
Most asymptomatic individuals with Gitelman syndrome can be monitored without medical treatment. Dietary modification of a high salt diet incorporated with, potassium and magnesium supplementation to normalize blood levels is the mainstay of treatment. Large doses of potassium and magnesium are often necessary to adequately replace the electrolytes lost in the urine.Diarrhea is a common side effect of oral magnesium which can make replacement by mouth difficult but dividing the dose to 3-4 times a day is better tolerated. Severe deficits of potassium and magnesium require intravenous replacement. If low blood potassium levels are not sufficiently replaced with replacement by mouth, aldosterone antagonists (such as spironolactone or eplerenone) or epithelial sodium channel blockers such as amiloride can be used to decrease urinary wasting of potassium.
In patients with early onset of the disease such as infants and children, indomethacin is the drug of choice utilized to treat growth disturbances. Indomethacin in a study by Blanchard et al. 2015 was shown to increase serum potassium levels, and decrease renin concentration. Adverse effects of indomethacin include a decrease in the glomerular filtration rate, and gastrointestinal disturbances.
Cardiac evaluation is promoted in the prevention of dysrhythmias and monitoring of QT interval activity. Medications that extend or prolong the QT interval (macrolides, antihistamines, beta-2 agonists) should be avoided in these patients to prevent cardiac death.
☝️ This is not a substitute for professional medical advice. Please consult with your physician before making any medical decision.
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