Bartter syndrome

Bartter syndrome

Other Names: Potassium wasting; Bartter's syndrome; Hypokalemic alkalosis with hypercalciuria

Bartter syndrome is a group of similar kidney disorders that cause an imbalance of potassium, sodium, chloride, and other molecules in the body.

In some cases, Bartter syndrome becomes apparent before birth. The disorder can cause polyhydramnios, which is an increased volume of fluid surrounding the fetus (amniotic fluid). Polyhydramnios increases the risk of premature birth.

Epidemiology

The exact prevalence of this disorder is unknown, although it likely affects about 1 per million people worldwide. The condition appears to be more common in Costa Rica and Kuwait than in other populations.

Types

Two major forms of Bartter syndrome are distinguished by their age of onset and severity. One form begins before birth (antenatal) and is often life-threatening. The other form, often called the classical form, begins in early childhood and tends to be less severe.

Once the genetic causes of Bartter syndrome were identified, researchers also split the disorder into different types based on the genes involved. Types I, II, and IV have the features of antenatal Bartter syndrome. Because type IV is also associated with hearing loss, it is sometimes called antenatal Bartter syndrome with sensorineural deafness. Type III usually has the features of classical Bartter syndrome.

Cause

• Bartter syndrome can be caused by mutations in at least five genes. Mutations in the SLC12A1 gene cause type I.
• Type II results from mutations in the KCNJ1 gene.
• Mutations in the CLCNKB gene are responsible for type III.
• Type IV can result from mutations in the BSND gene or from a combination of mutations in the CLCNKA and CLCNKB genes.
• The genes associated with Bartter syndrome play important roles in normal kidney function. The proteins produced from these genes are involved in the kidneys' reabsorption of salt. Mutations in any of the five genes impair the kidneys' ability to reabsorb salt, leading to the loss of excess salt in the urine (salt wasting). Abnormalities of salt transport also affect the reabsorption of other charged atoms (ions), including potassium and calcium. The resulting imbalance of ions in the body leads to the major features of Bartter syndrome.
• In some people with Bartter syndrome, the genetic cause of the disorder is unknown. Researchers are searching for additional genes that may be associated with this condition.

Inheritance

Autosomal recessive inheritance, a 25% chance

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Signs and symptoms

• The signs and symptoms associated with Bartter syndrome can vary depending on the form of Bartter syndrome an affected individual has. The antenatal forms (beginning before birth) can be life-threatening, while the classical form, beginning in early childhood, tends to be less severe.
• The antenatal forms of Bartter syndrome (types I, II and IV) may first be characterized by abnormally high levels of amniotic fluid surrounding the affected fetus (polyhydramnios); premature delivery; and possibly life-threatening salt (sodium-chloride) loss. Affected newborns may experience excessive urination (polyuria) and life-threatening episodes of fever and dehydration. Vomiting and diarrhea may also occur. Some affected infants have distinctive facial features (triangular face, prominent forehead, large eyes, protruding ears, and drooping mouth), failure to thrive, delayed growth, and/or intellectual disability. Individuals with type IV may also have sensorineural deafness (hearing loss caused by abnormalities in the inner ear).
• Classical Bartter syndrome typically becomes apparent in childhood and is characterized by muscle weakness, cramping, spasms, and fatigue. Excessive thirst (polydipsia), excessive urination and the need to urinate at night (nocturia) may also be present. This can lead to dehydration. Some children crave salt. Additional symptoms include constipation, vomiting, elevated body temperature, growth delay and developmental delay.
• Some individuals with Bartter syndrome have significant electrolyte imbalances which can lead to irregular heartbeats (cardiac arrhythmias). This can increase the risk for sudden cardiac arrest. Another complication is excessive levels of calcium in the kidneys (nephrocalcinosis). This can lead to blood in the urine, vomiting, and fever. Over time, this calcium buildup can affect kidney function.

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.

80%-99% of people have these symptoms

• Abnormality of metabolism/homeostasis(Laboratory abnormality)

5%-29% of people have these symptoms

• Hyperparathyroidism(Elevated blood parathyroid hormone level)
• Hypocalciuria(Low urine calcium levels)
• Hypomagnesemia(Low blood magnesium levels)

Diagnosis

• Bartter syndrome is usually diagnosed after a combination of tests are performed on an individual with the signs and symptoms of the condition. Laboratory tests include blood tests to measure serum electrolyte levels (specifically magnesium, renin, and aldosterone), and urine tests to determine the presence of prostaglandin E2 and urine electrolytes (including elevated levels of sodium and potassium).
• Antenatal subtypes can be diagnosed before birth (prenatally) when polyhydramnios is present without associated congenital malformations and when there are elevated levels of chloride and aldosterone in the amniotic fluid. Molecular genetic testing can be used to confirm the diagnosis.

Treatment

Treatment of Bartter syndrome depends on the specific symptoms present in each individual and may require the coordinated efforts of a team of specialists. The primary focus of treatment is on restoring the proper balance of fluids and electrolytes in the body. This may include oral potassium (K) supplements, medication such as indomethacin, and potassium-sparing diuretics. In high-stress situations such as illness or trauma, blood electrolyte levels can change rapidly, which may require immediate intravenous treatment. Genetic counseling may benefit affected individuals and their families.

Prognosis

Currently there is no cure for Bartter syndrome, but treatments are available. Severity of symptoms (and associated complications) vary from person to person. People with Bartter syndrome must take medications consistently, as prescribed, throughout their lifetime. They also must be careful to maintain an adequate fluid and electrolyte balance. With treatment, prognosis in many cases is good. However, life expectancy and quality of life may be affected by complications such as growth delays, developmental problems, kidney failure and multiple hospitalizations.

NIH genetic and rare disease info

• NIH info on Bartter syndrome

Bartter syndrome is a rare disease.

Bartter syndrome Resources
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