Other Structural Variants

Other Structural Variants

Hemoglobin C: HbC is a beta globin gene variant. Glutamic acid in the 6th position of the beta chain is replaced by lysine. Red Blood cells containing HbC are more rigid than normal.

Genotypes: HbAC, HbCC, HbC-beta, HbC/HPFH


Hemoglobin D: HbD is a beta globin gene variant. Hemoglobin D-Punjab, D los-Angeles are identical. In both types there is substitution of glutamic acid for lysine.

Genotypes: Hb D-Punjab/Beta Thal, Hb D-Punjab Trait


Hemoglobin O Arab: HbO is a beta globin chain variant. Glutamic acid in 121st position is replaced by glutamine due to point mutation.

Genotypes: Hb O Arab Trait, Hb O Arab Beta Plus or Beta 0.

Hemoglobin E: E Beta Thalassemia: Hemoglobin E is one of the most common abnormal hemoglobins. It is usually found in people of Southeast Asian ancestry, such as Cambodians, Vietnamese and Thai. When combined with beta thalassemia, hemoglobin E produces E beta thalassemia, a moderately severe anemia which is similar in symptoms to beta thalassemia intermedia.


Hemoglobin G Philadelphia: HbG is an alpha chain variant. Two different mutations are reported. Substitution of Asparagine for lysine in 68th position of alpha chain.

Hereditary persistent fetal Hemoglobin (HPFH)

  • It results from complete absence of beta and delta chain.
  • It was first described in West Africa in Jamaican family.
  • HPFH results due to mutation within beta globin cluster that alters normal Hb switching.

Hereditary persistent fetal Hemoglobin (HPFH) Types

  • Pan cellular HPFH
  • Heterocellular HPFH

Pan cellular HPFH: HbF is distributed uniformly.
Heterocellular HPFH: HbF is distributed heterogeneously.

Genetics

Two different molecular mechanisms can result in HPFH
Deletional HPFH: Result from specific large deletion in beta globin gene cluster involving HBB
Non Deletional HPFH: Result from point mutation in the promoter of gamma globin gene HBG1, HBG2.

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