A genetic description that does not contain Bart’s hemoglobin at birth would be a description of the genetic makeup of a family member other than Bart.
hemoglobin bartsabbreviated hb bartsit’s an abnormal kind of hemoglobin which consists of four gamma globins. It is moderately insoluble and therefore accumulates in the red blood cells. Hb Barts has a high affinity for oxygen, so it cannot deliver oxygen to the tissue. Therefore, this makes it an inefficient oxygen carrier. as a embryo develops, begins to produce alpha-globins in weeks 5–6 of development. When both HBA1 and HBA2 genes encoding alpha globins become dysfunctional, affected fetuses will have difficulty synthesizing a functional hemoglobin. As a result, the gamma chains will accumulate and form four gamma globins. These gamma globins bind together to form hemoglobin Barts. It is produced in disease alpha thalassemia and in the most severe cases, it is the only form of circulating hemoglobin. In this situation, a fetus will develop hydrops fetalis and usually die before or shortly after birth unless intrauterine blood transfusion is performed.
Because Barts hemoglobin is elevated in alpha thalassemia, it can be measured, providing a useful screening test for this disease in some populations.
The ability to measure Barts hemoglobin makes it useful in newborn screening tests. If Barts hemoglobin is detected in a newborn screening, the patient is usually referred for further evaluation, as the detection of Barts hemoglobin can indicate a deletion of the alpha globin gene, making the baby a silent carrier of alpha thalassemia, or two deletions of the alpha globin gene (alpha thalassemia), or hemoglobin H disease (three deletions of the alpha globin gene). The deletion of four alpha globin genes was previously considered incompatible with life, but there are currently 69 patients who have survived past infancy.
|Genotypes||Alpha globin gene deletions||Clinical Component|
|–/αα or -α/-α||two||Alpha-Thalassaemic Trait|
|–/-α||3||Hb H disease|
Table 1: α represents the presence of the α-globin gene and- represents the deletion of the α-globin gene.
The chance that a fetus will develop hydrops fetalis of Bart’s hemoglobin depends on whether one or both parents carry the alpha-thalassemia trait. Because it is a disease incompatible with life, the diagnosis is made during prenatal care. Early detection of Bart’s Hemoglobin (Hb) disease before hydrops fetalis develops is crucial because fetuses who develop hydrops fetalis will be stillborn or may die soon after birth. There may be early termination of pregnancy to avoid serious complications for the baby or the mother. Studies show that at 11 to 14 weeks of gestation, ultrasound markers can associate affected and unaffected pregnancies. The most sensitive marker was found to be the CT and MCA-PSV ratio.
Parents at risk of having a child with Fetal Hydrops can continue the pregnancy with regular ultrasounds and intrauterine blood transfusion. The babies of these parents are born without edema or major neurological defects, and eventually this disease can be cured with Hematopoietic stem cell transplantation. A newly developed diagnostic test called Immunochromatography (IC) Strip Tests uses monoclonal antibodies to detect Hemoglobin Barts in red blood cell lysate. This diagnostic test is validated for positive and negative predictive values. It’s also cheap and easy, making regular screening for alpha thalassemia a plausible possibility.
Anemia is a factor in fetuses with hemoglobin Bart’s disease as there is an “increased cardiac output” and hypovolaemia as the fetal tissues require oxygen due to the high affinity of gamma globulin for oxygen. This deprives tissues of oxygen to function well. Symptoms of anemia occur in the first trimester.
This hemoglobin variant is so named because it was discovered in Saint Bartholomew Hospital in London, often shortened to Barts.
Source: Hemoglobin Barts
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