From the Guidelines
Bartter syndrome type 5 is characterized by specific biochemical abnormalities resulting from mutations in the MAGED2 gene, leading to hypokalemia, metabolic alkalosis, and normal or low blood pressure. The key biochemical features of Bartter syndrome type 5 include:
- Hypokalemia (low potassium levels)
- Metabolic alkalosis (elevated blood pH)
- Normal or low blood pressure despite elevated renin and aldosterone levels
- The gene affected in Bartter syndrome type 5 is MAGED2, which regulates the expression of proteins involved in salt reabsorption in the thick ascending limb of the loop of Henle 1. The mode of inheritance of Bartter syndrome type 5 is X-linked recessive, which is distinct from the autosomal recessive inheritance pattern of other Bartter syndrome types 1. The pathophysiology of Bartter syndrome type 5 involves impaired salt reabsorption in the thick ascending limb, leading to a reduction of calcium reabsorption and hypercalciuria, as well as a progressive reduction or complete blunting of the osmotic gradient in the renal medulla, causing isosthenuria 1. The biochemical profile of Bartter syndrome type 5 also includes increased urinary prostaglandin E2 levels and resistance to the blood pressure-raising effects of angiotensin II, although the exact mechanisms are not fully understood 1. It is essential to note that the diagnosis of Bartter syndrome type 5 should be considered in the presence of renal salt wasting, polyuria, rapid weight loss, and signs of dehydration, and confirmed by genetic analysis whenever possible 1.
From the Research
Biochemical Features of Bartter Type Five Syndrome
The biochemical features of Bartter type five syndrome include:
- Hypokalemia, which may occur later in life and can be corrected with small doses of oral potassium 2
- Absence of alkalosis, unlike other types of Bartter syndrome 2
- Normal or mildly activated plasma renin and aldosterone production 2
- Conserved natriuretic response to furosemide, a inhibitor of sodium reabsorption in the thick ascending limb of the loop of Henle (TALH) 2
- Hyperreninemic hyperaldosteronism, although this may not be as pronounced as in other types of Bartter syndrome 3
- Hypochloremic metabolic alkalosis, although this may not be present in all cases of type 5 Bartter syndrome 3
- Renal salt wasting, which can lead to polyuria and polydipsia 4
Comparison to Other Types of Bartter Syndrome
Type 5 Bartter syndrome is distinct from other types of the disease, with a milder phenotype and later onset of symptoms 2. The biochemical features of type 5 Bartter syndrome are also different from those of other types, with less pronounced hyperreninemic hyperaldosteronism and absence of alkalosis 2, 3. However, all types of Bartter syndrome are characterized by hypokalemia, metabolic alkalosis, and renal salt wasting, although the severity and presentation of these features can vary 5, 3, 4, 6