Barth syndrome
medical conditions

Barth syndrome

Explore the available health information, treatment context, and integrative evidence for Barth syndrome.

Background
  • Barth syndrome is a rare metabolic and neuromuscular disorder that appears to only affect males. At birth or a few months after birth, infants typically have reduced muscle tone and an enlarged heart that does not pump efficiently. Other characteristics of Barth syndrome include muscle weakness, fatigue, short stature, and frequent infections (caused by a weakened immune system).
  • Researchers estimate that Barth syndrome affects at least 50 families worldwide, but some experts believe that Barth syndrome is under-diagnosed. Quality studies determining the prevalence of the disorder are lacking. However, it is estimated that fewer than 10 babies are born with Barth syndrome each year in the United States. This suggests an incidence rate of one out of 300,000-400,000 births. On average, 50% of children born to a carrier mother will inherit the defective gene, but only boys will have symptoms. All daughters born to an affected male will be carriers.
  • There is currently no cure or specific treatment for Barth syndrome. Instead, treatment focuses on reducing the symptoms and preventing complications, such as infections. Severe infections and heart failure are common causes of death in affected children. Early diagnosis and treatment are essential for prolonged survival for boys born with Barth syndrome.
Risk Factors and Causes
  • Mutated gene: Barth syndrome occurs when a person is born with a mutated, or abnormal, TAZ1 (or G4.5) gene. This abnormal gene is located on the X chromosome, which is a sex-determining chromosome. Males have one X and one Y chromosome, while females have two X chromosomes.
  • Inheritance: The mutated TAZ1 gene is passed down as an X-linked recessive trait. Since males have only one X chromosome, they will develop the disorder if they inherit just one copy of the mutated gene.
  • Females, on the other hand, would need to inherit two copies of the mutated gene (one in each of their two X chromosomes) in order to develop Barth syndrome. Although this could theoretically happen, there have been no reports of females who have Barth syndrome. Instead, females are typically carriers of Barth syndrome. This means that a female can have one copy of the mutated gene without experiencing symptoms of Barth syndrome.
  • Even though a mother who carries the mutated gene does not have the disorder, she can pass her mutated gene to each of her children. There is a 50% chance that a female carrier will pass her X chromosome to a son, and her son will develop the disorder. If the woman has a daughter, there is a 50% chance that the girl will be a carrier.
  • If a father has Barth syndrome, there is a 100% chance that each of his daughters will carry the mutated gene. Carriers can then pass their mutated genes to their children.
Signs and Symptoms
  • General: Most people with Barth syndrome experience all of the symptoms listed below. However, some people may have only a few of these abnormalities and, as a result, they are often misdiagnosed.
  • Cardiomyopathy: As infants, patients typically have cardiomyopathy, a condition that occurs when the heart is enlarged and unable to pump efficiently. Common symptoms of cardiomyopathy include difficulty breathing, poor appetite, irregular heartbeat, and slow weight gain.
  • Metabolism: The mitochondria, cellular structures which produce energy for cells, do not function properly in people with Barth syndrome. This is because a genetic mutation prevents the mitochondria from making enough of a lipid called tetralinoleoyl-cardiolipin. This is the main phospholipid of the mitochondrial inner membrane. Thus, patients with Barth syndrome typically have high levels of an organic acid, called 3-methylglutaconic acid, in their bodies.
  • Musculoskeletal: People born with Barth syndrome typically have delayed motor skills, reduced muscle tone (called hypotonia), and delayed growth, all of which may lead to varying degrees of physical disabilities.
  • Weakened immune system: People with Barth syndrome have weakened immune systems because they are born with abnormally low levels of white blood cells, called neutrophils. When there are not enough of these cells in the body, the condition is called neutropenia. Neutrophils make up 70% of all white blood cells in the body and are especially important in fighting off infections and diseases. Therefore, people with neutropenia have an increased risk of becoming sick.
  • Other: People with Barth syndrome typically experience chronic fatigue, low blood sugar levels (called hypoglycemia), diarrhea, and varying degrees of learning disabilities.
Diagnosis
  • General: If Barth syndrome is suspected, medical tests, such as a urine analysis and complete blood count, may be performed. If these tests indicate Barth syndrome, a diagnosis can be confirmed with DNA testing. Other tests, such as an echocardiogram, may be performed to determine the severity of the condition.
  • Urine analysis: Most patients with Barth syndrome will have elevated levels of an organic acid, called 3-methylglutaconic acid, in their urine.
  • Complete blood count: A doctor may take a sample of the patient's blood to determine if he/she has low levels of neutrophils in his/her blood.
  • DNA test: A DNA test may be performed to confirm a diagnosis. A sample of the patient's blood is taken and analyzed in a laboratory for the presence of a mutated TAZ1 gene. If a mutation is present, a positive diagnosis is made.
  • If a female has a family history of Barth syndrome, a DNA test may be performed to determine if she carries a copy of the mutated TAZ1 gene. Although a carrier does not have Barth syndrome, she may pass a copy to her children.
  • Prenatal DNA testing: If a parent is a carrier of the mutated TAZ1 gene, prenatal testing may be performed at a hospital to determine if the fetus has the disorder. These types of tests are considered outpatient procedures. However, there are serious risks associated with prenatal tests, including miscarriage. Patients should discuss the potential health benefits and risks associated with these procedures before making any medical decisions.
  • During amniocentesis, a long, thin needle is inserted through the abdominal wall and into the uterus. A small amount of amniotic fluid is removed from the sac surrounding the fetus. The fluid is then analyzed for a mutated TAZ1 gene. This test is performed after 15 weeks of gestation. The risk of miscarriage ranges from one out of 200-400 patients. Some patients may experience minor complications, such as cramping, leaking fluid, or irritation where the needle was inserted.
  • During chorionic villus sampling (CVS), a small piece of tissue (chorionic villi) is removed from the placenta during early pregnancy. Depending on where the placenta is located, CVS can be performed through the cervix or through the abdomen. The tissue sample is then analyzed for a mutated TAZ1 gene. This procedure may be performed between the ninth and 14th week of gestation. The risks of infection or fetal damage are slightly higher than the risks of amniocentesis. Miscarriage occurs in about two percent of women who undergo this procedure.
  • Genetic counseling: Before and after genetic testing, it is recommended that people meet with genetic counselors. These professionals can help patients understand the risks of having a child with Barth syndrome. A genetic counselor can also explain the different types of genetic tests, including their potential risks and benefits. These counselors can also help patients understand the results and limitations of these tests.
  • Echocardiogram: An echocardiogram may also be performed to detect possible abnormalities in the heart muscle. This test is similar to an ultrasound that is used in pregnant women. A wand-like device (called a transducer) is rubbed on the patient's chest and sound waves produce images of the heart.
Complications
  • Blood clots: Cardiomyopathy makes patients more likely to develop blood clots. These blood clots may block blood vessels and block blood flow to important organs, including the brain, heart, and lungs. If blood flow to the heart is blocked, it may lead to a heart attack, and if blood flow to the brain is blocked, it may cause a stroke.
  • Cardiac arrest: Cardiomyopathy may cause irregular heartbeats. Sometimes the heart may beat too slowly to properly circulate blood throughout the body. Sometimes the heart beats too quickly to allow the heart to beat efficiently. Abnormal heartbeats may result in fainting. In serious cases, irregular heartbeats may cause the heart to suddenly stop beating (called cardiac arrest), and the patient is at risk of dying.
  • Heart failure: People with Barth syndrome typically have cardiomyopathy. Their hearts are enlarged and unable to pump as efficiently as healthy people. This increases the risk of experiencing heart failure, a degenerative condition that occurs when the heart is unable to beat efficiently and pump enough blood to meet the body's needs. Unlike cardiac arrest, which occurs when the heart suddenly stops working, heart failure is a long-term condition that generally worsens over time.
  • Severe infections: People with Barth syndrome have weakened immune systems because they have low levels of neutrophils in their blood. As a result, they have an increased risk of developing infections, which may be severe. If an infection enters the bloodstream, it may spread to vital organs and become a life-threatening condition.
Treatment
  • General: There is currently no cure or specific treatment for Barth syndrome. Instead, treatment focuses on reducing the symptoms and preventing complications, such as infections.
  • Physical therapy: Physical therapy may help patients improve their physical strength and motor coordination. Since babies with Barth syndrome usually have reduced muscle tone, a physical therapist may be able to help babies learn how to roll over, sit up, and walk. A variety of techniques, including exercises, stretches, traction, electrical stimulation, and massage, may be used during physical therapy sessions.
  • Antibiotics: Medications, called antibiotics, are used to treat bacterial infections, commonly associated with Barth syndrome. These medications kill the disease-causing bacteria. The exact type, dose, and duration of treatment depend on the type of infections, as well as the patient's age and overall health.
  • Side effects of antibiotics vary depending on the specific type of medication used. People should not stop taking antibiotics early, even if symptoms start to go away, because bacteria may still be present in the body. Stopping medication early may allow the infection to return and lead to antibiotic resistance. This is because the most resilient bacteria are the last to be killed. If medication is stopped, the bacteria may become resistance to treatment, and the medications will no longer be effective if taken in the future.
  • Granulocyte colony stimulating factor (GCSF): A medication, called granulocyte colony stimulating factor (G-CSF), has been used to help stimulate the production of neutrophils (which are also called granulocytes) in the bone marrow. As a result, this helps the body fight against infections.
  • Side effects are rare and may include bone pain, tenderness at the injection site, and high levels of lactate dehydrogenase and alkaline phosphatase in the blood.
  • Lifestyle: People with cardiomyopathy are encouraged not to smoke or gain excessive weight. They are also encouraged to eat a low-salt diet, participate in moderate exercise (30 minutes or more) on most days of the week, and limit or avoid alcohol consumption.
  • Heart medications: Patients with cardiomyopathy often require medications. Doctors may prescribe angiotensin-converting enzyme (ACE) inhibitors, such as enalapril (Vasotec®), lisinopril (Zestril® or Prinivil®), ramipril (Altace®), and captopril (Capoten®), to improve the heart's ability to pump blood. Side effects of ACE-inhibitors may include chronic, nonproductive cough (occurs in about 10% of patients), dizziness or weakness (caused by low blood pressure), increased potassium levels, skin rashes, and sudden swelling of the lips, face, and cheeks.
  • In addition, diuretics, such as furosemide (Lasix®), may help reduce fluid retention. Side effects of diuretics may include frequent urination and low potassium levels in the blood. Because of this, blood tests are performed periodically and a potassium supplement is prescribed if blood levels of potassium are low. Individuals may be asked to eat more fruits high in potassium, such as bananas and oranges, while on diuretic therapy.
  • Beta blockers, such as atenolol (Tenormin®), carvedilol (Coreg®), and metoprolol (Lopressor® or Toprol XL®), may improve the heart's function and reduce the risk of death. During the first several weeks of treatment, some patients experience worsening symptoms due to a decrease in oxygen circulation in the body. Other side effects may include low blood pressure, difficulty breathing, sexual dysfunction, nausea, and weakness with exertion.
  • Pacemaker: Some patients may benefit from pacemakers that regulate the contractions of the heart between the left and right ventricles. These pacemakers are surgically inserted into the heart. It is considered an inpatient procedure because patients typically stay in the hospital for one to three days after having a pacemaker implanted. The pacemaker is programmed to fit the patient's particular pacing needs. A return visit is scheduled to refine the settings. The battery-life of pacemakers is about 10 years. When the battery is low, the pacemaker is surgically replaced.
  • It is normal for the surgical wound to be somewhat painful and swollen for a few days after the procedure. This can usually be treated with medications, such as ultram (Tramadol®) or ibuprofen (Motrin®). The wound may also appear mildly red for a few days. However, if the area of redness enlarges, a doctor should be notified due to the potential for a serious infection. If there are no other problems, most individuals who have a permanent pacemaker surgically implanted can go home the next day. They can usually return to normal activities within six weeks. For several weeks after having a pacemaker implanted, the individual may be asked not to lift more than five pounds or raise the affected arm over his/her shoulder.
  • Heart transplant: Patients with serious cardiomyopathy may develop heart failure, which is fatal unless treated with a heart transplant. However, people often have to wait several months to years before a heart is available that matches the patient's. Sometimes a person can be supported with mechanical heart assistance devices, called ventricular assist devices (VADs) as they wait for a heart. If a person with heart failure is not a candidate for a heart transplant, a VAD may provide long-term support.
Prevention
  • There is currently no known method of prevention for Barth syndrome.
  • If a female has a family history of Barth syndrome, genetic testing may be performed to determine if she carries the mutated gene. Although carriers do not have the disease, they can pass copies of their mutated gene to each of their children.
  • Prenatal DNA testing may be performed if there is a family history of Barth syndrome. However, there are health risks associated with prenatal testing, including miscarriage. Therefore, patients should discuss the potential health risks and benefits with their healthcare provider before making any health-related decisions.
  • Before and after genetic testing, it is recommended that people meet with genetic counselors. These professionals can help patients understand the risks of having a child with Barth syndrome. A genetic counselor can also explain the different types of genetic tests, including their potential risks, benefits, and limitations. These counselors can help patients understand the results and limitations of these tests.
  • People who are diagnosed with Barth syndrome can help reduce their risk of acquiring infections. For instance, people are encouraged to avoid close contact with individuals who have contagious illnesses. Practicing good hygiene and regularly washing the hands with soap and water may also help reduce the risk of acquiring infections. In addition, antibiotics should only be taken when prescribed. This helps reduce the risk of developing antibiotic-resistant bacterial infections in the future.
References
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  10. Schlame M, Ren M. Barth syndrome, a human disorder of cardiolipin metabolism. FEBS Lett. 2006 Oct 9;580(23):5450-5. Epub 2006 Jul 17.
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