CH. 24 - Hemoglobinopathies

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mama mo mukhang sickle cell

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46 Terms

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Hemoglobinopathies

Results from a genetic mutation in one or more genes that affect hemoglobin synthesis

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Qualitative Hemoglobinopathies

The hemoglobin molecule has an altered amino acid sequence within the globin chains

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Quantitative Hemoglobinopathies

Thalassemias result in a reduced rate of hemoglobin synthesis but do not affect the amino acid sequence of the affected globin chains.

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Point Mutation

  • The most common type of genetic mutation

  • Replacement of one original nucleotide in the normal gene with a different nucleotide.

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Gene fusions

Occurs when two normal genes break between nucleotides, switch positions, and anneal to the opposite gene

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Zygosity

Refers to the association between the number of gene mutations and the level of severity of the resultant genetic defect

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Sickle Cell Disease (SCD)

This is the most common form of hemoglobinopathy

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Hb S

  • Type of Hb in which sickling occurs when a solution of RBCs is deficient in oxygen.

  • Resistant against infection with P. falciparum

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Reversible Sickle Cells

  • RBCs that change shape in response to oxygen tension.

  • Circulate as normal biconcave disc.

  • Able to travel into the microvasculature.

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Irreversible Sickle Cells

  • RBCs do not change their shape.

  • Seen as elongated sickle cells with a point at each end.

  • Recognized as abnormal by the spleen and removed from circulation

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Hemoglobin solubility test

The most common screening test for Hb S.

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Alkaline hemoglobin electrophoresis

Based on the separation of hemoglobin molecules in an electric field, the result of differences in total molecular charge

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High-Performance Liquid Chromatography (HPLC)

  • Used to confirm hemoglobin variants.

  • More automated

  • Separates hemoglobin types in a cation exchange columns

  • Best used in the diagnosis of thalassemia.

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Capillary Electrophoresis

  • Separates hemoglobin types based on charge in an alkaline buffer

  • Use smaller volumes and produce better separation than traditional agarose electrophoresis

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Isoelectric focusing

It is a confirmatory technique that is expensive and complex, requiring well-trained and experienced laboratory personnel

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Hb C-Harlem

  • Type of Hb that has a Double - Substitution on the Beta Chain.

  • The substitution of valine for glutamic acid at position 6 of the beta chain and the substitution at position 73 of aspartic acid for asparagine

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Hb S-β-Thalassemia

Type of Hb that resembles mild or moderate SCD

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Hb S-Korle Bu

It is a rare hemoglobin variant with substitution of aspartic acid for asparagine at position 73 of the b chain

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Hb M

The mutation in the Alpha, Beta, and Gamma Globin Genes results in the production of this Hb.

It also causes blood specimens to appear brown

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Cyanosis

This is produced when iron in the ferric state is unable to carry oxygen.

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Hb Köln

This is the most prevalent unstable hemoglobin

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Plasmodium falciparum

This parasite is most associated with SCD

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Vasoocclusive crisis

This is the hallmark of SCD

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Spleen sequestration

This is characterized by a sudden trapping of blood in the spleen, which leads to a rapid decline in hemoglobin

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Autosplenectomy

Gradual loss of splenic function is referred to as?

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Fat embolism syndrome (FES)

A rare but often fatal sequalae of SCD

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Aplastic episodes

The most common life-threatening hematologic complications and are usually associated with infection, particularly parvovirus infection

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Megaloblastic episodes

These episodes result from the sudden arrest of erythropoiesis caused by folate depletion

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Avascular necrosis (AVN)

Impaired blood supply to the head of the femur and humerus results in a condition called

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Hand-foot syndrome

This is characterized by pain and swelling in the hands and feet of children younger than 3 years

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Hb C

Type of Hb that is found primarily in people of African descent

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Decreased production of a globin chain

REVIEW QUESTION:

A qualitative abnormality in hemoglobin may involve all of the following except:

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Polymerizes to form tactoid crystals

REVIEW QUESTION:

The substitution of valine for glutamic acid at position 6 of the b chain of hemoglobin results in hemoglobin that:

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Higher levels of Hb F are present

GUIDE QUESTIONS:

Patients with SCD usually do not exhibit symptoms until 6 months of age because:

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Folic acid

Megaloblastic episodes in SCD can be prevented by prophylactic administration of:

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Hemoglobin electrophoresis at acid pH

Which of the following is the most definitive test for Hb S?

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Substitution of lysine for glutamic acid at position 6 of the b chain

REVIEW QUESTION:

A patient presents with mild normochromic, normocytic anemia. On the peripheral blood film, there are a few target cells, rare nucleated RBCs, and hexagonal crystals within and lying outside of the RBCs. Which abnormality in the hemoglobin molecule is most likely?

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The patient has Hb M.

REVIEW QUESTION:

A well-mixed specimen obtained for a CBC has a brown color. The patient is being treated with a sulfonamide for a bladder infection. Which of the following could explain the brown color?

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25%

REVIEW QUESTION:

Through routine screening, prospective parents discover that they are both heterozygous for Hb S. What percentage of their children potentially could have sickle cell anemia (Hb SS)?

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Vasoocclusion

REVIEW QUESTION:

Painful crises in patients with SCD occur as a result of:

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Are insoluble in reduced, deoxygenated form

REVIEW QUESTION:

The screening test for Hb S that uses a reducing agent, such as sodium dithionite, is based on the fact that hemoglobins that sickle:

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Homozygous/disease

REVIEW QUESTION:

DNA analysis documents a patient has inherited the sickle mutation in both b-globin genes. The two terms that best describe this genotype are:

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Sub-Saharan Africa

REVIEW QUESTION:

In which of the following geographic areas is Hb S most prevalent?

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Hb E

REVIEW QUESTION:

Which hemoglobinopathy is more common in Southeast Asian patients?

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Hb SG

REVIEW QUESTION:

Which of the following Hb S compound heterozygotes exhibits the mildest symptoms?

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Only homozygotes are symptomatic

REVIEW QUESTION:

Unstable hemoglobins exhibit all of the following findings except: