Hemoglobin C
Encyclopedia
Hemoglobin C is an abnormal hemoglobin
with substitution of a lysine
residue for a glutamic acid
residue at the 6th position of the β-globin chain.
. In those who are heterozygous
for the mutation, about 28–44% of total hemoglobin (Hb) is HbC, and no anemia
develops.
In homozygotes
, nearly all Hb is in the HbC form, resulting in mild hemolytic anemia
.
) or for HbC and thalassemia
are known, and have atypical hemolytic anemias; sickling is enhanced in Hb SC disease.
Hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...
with substitution of a lysine
Lysine
Lysine is an α-amino acid with the chemical formula HO2CCH4NH2. It is an essential amino acid, which means that the human body cannot synthesize it. Its codons are AAA and AAG....
residue for a glutamic acid
Glutamic acid
Glutamic acid is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid. The carboxylate anions and salts of glutamic acid are known as glutamates...
residue at the 6th position of the β-globin chain.
Clinical significance
This mutated form reduces the normal plasticity of host erythrocytes causing a hemoglobinopathyHemoglobinopathy
Hemoglobinopathy is a kind of genetic defect that results in abnormal structure of one of the globin chains of the hemoglobin molecule. Hemoglobinopathies are inherited single-gene disorders; in most cases, they are inherited as autosomal co-dominant traits. Common hemoglobinopathies include...
. In those who are heterozygous
Zygosity
Zygosity refers to the similarity of alleles for a trait in an organism. If both alleles are the same, the organism is homozygous for the trait. If both alleles are different, the organism is heterozygous for that trait...
for the mutation, about 28–44% of total hemoglobin (Hb) is HbC, and no anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
develops.
In homozygotes
Zygosity
Zygosity refers to the similarity of alleles for a trait in an organism. If both alleles are the same, the organism is homozygous for the trait. If both alleles are different, the organism is heterozygous for that trait...
, nearly all Hb is in the HbC form, resulting in mild hemolytic anemia
Hemolytic anemia
Hemolytic anemia is a form of anemia due to hemolysis, the abnormal breakdown of red blood cells , either in the blood vessels or elsewhere in the human body . It has numerous possible causes, ranging from relatively harmless to life-threatening...
.
Presentation
Target cells, microspherocytes and HbC crystals are found in a blood smear from a homozygous patient.Combinations with other conditions
Individuals heterozygous for both HbC and Hb S (Hb Sickle-cell diseaseSickle-cell disease
Sickle-cell disease , or sickle-cell anaemia or drepanocytosis, is an autosomal recessive genetic blood disorder with overdominance, characterized by red blood cells that assume an abnormal, rigid, sickle shape. Sickling decreases the cells' flexibility and results in a risk of various...
) or for HbC and thalassemia
Thalassemia
Thalassemia is an inherited autosomal recessive blood disease that originated in the Mediterranean region. In thalassemia the genetic defect, which could be either mutation or deletion, results in reduced rate of synthesis or no synthesis of one of the globin chains that make up hemoglobin...
are known, and have atypical hemolytic anemias; sickling is enhanced in Hb SC disease.