![]() This altered hemoglobin gives the blood a brown color and causes a bluish appearance of the skin, lips, and nails (cyanosis). In methemoglobinemia, beta-globin type, variants in the HBB gene alter the beta-globin protein and promote the heme iron to change from ferrous to ferric. Hemoglobin that contains ferric iron is known as methemoglobin and is unable to efficiently deliver oxygen to the body's tissues. The iron within the heme can change to another form of iron called ferric iron (Fe 3+), which cannot bind to oxygen. For hemoglobin to bind to oxygen, the iron within the heme molecule needs to be in a form called ferrous iron (Fe 2+). These variants often affect the region of the protein that binds to heme. Variants in the HBB gene have been found to cause methemoglobinemia, beta-globin type, which is a condition that alters the hemoglobin within red blood cells. A lack of oxygen in the body's tissues can lead to poor growth, organ damage, and other health problems associated with beta thalassemia. ![]() A shortage of mature red blood cells can reduce the amount of oxygen that is delivered to tissues to below what is needed to satisfy the body's energy needs. A lack of hemoglobin disrupts the normal development of red blood cells. Problems with the subunits that make up hemoglobin, including low levels of beta-globin, reduce or eliminate the production of this molecule. Variants that prevent cells from producing any beta-globin result in beta-zero (β 0) thalassemia. ![]() HBB gene variants that decrease beta-globin production result in a condition called beta-plus (β +) thalassemia. Other variants insert or delete a small number of nucleotides in the HBB gene. Most of the variants involve a change in a single DNA building block (nucleotide) within or near the HBB gene. Hundreds of variants (also known as mutations) in the HBB gene have been found to cause beta thalassemia.
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