HEMOGLOBINOPATHIES Flashcards
-refers to a disease state involving the hemoglobin molecule
- are the most common genetic diseases
HEMOGLOBINOPATHIES
all hemoglobinopathies result from a ββββin one or more genes that affect hemoglobin synthesis
point mutation
- the genes that are mutated can code or either the proteins that make up the hemoglobin molecule or the proteins involved in synthesizing or regulating synthesis of the globin chains,
HEMOGLOBINOPATHIES
affects hemoglobin synthesis in one of two ways:
qualitatively HMOGLOBINOPATHIES
quantitatively THALASSEMIA
Factors that may alter the manner in which globin chains fold:
a. Change in amino acid charge
b. Size of the substituted amino acid
Detection and Identification of Hemoglobinopathies
Purpose -Primary screening procedure
Specimen -Whole blood (EDTA/heparin)
pH Alkaline 8.4
Principle -At alkaline buffer, hemoglobin is negatively charged and will migrate towards the anode
Cellulose acetate electrophoresis
Purpose -Confirm variants of hemoglobin
Specimen -Whole blood (EDTA)
pH Acid 6.0-6.2
Principle: In an acid pH, some hemoglobins assume a negative charge and migrate toward the anode, while others are positively charged and migrate toward the cathode
Citrate agar electrophoresis
- are the most common form of hemoglobinopathy
- are either homozygous for Hb S or are compound heterozygotes
- Hb S polymers are long and thin
SICKLE CELL DISEASE
-Separate Hb type in cation exchange column and usually requires only one sample injection
- can identify and quantitate low levels of Hb A2 and HbF
HPLC
-Best used in diagnosis of thalassemia rather than hemoglobinopathies
- also commonly used to quantitate HbA1c
HPLC
- defined by the structural formula Ξ±2B26GluβVal, which indicates that on the Ξ² chain at position 6, glutamic acid is replaced by valine
Hb SS
offer some protection against cerebral falciparum malaria
Hb SS
Sickle cells come in two forms:
a. Reversible sickle cells - change in shape in response to oxygen tension
b. Irreversible sickle cells - do not change their shape regardless of the change in oxygen tension or degree
of hemoglobin polymerization
Clinical Features:
Hallmark of SCD:
-Vasoocclusive crisis
- Acute chest syndrome
- Pulmonary hyprtension
- Increased susceptibility to S. aureus, S. pneumoniae, H. influenzae
- Aplastic episodes
Laboratory findings: SICKLE CELL DISEASE /Hb SS
Hallmark:
presence of sickle cells and target cells
- refers to the heterozygous state (Hb AS)
- generally asymptomatic and present with no clinical or hematologic manifestations
- failure to concentrate urine is the only consistent abnormality found in patients with sickle cell disease
Sickle cell trait
Sickle cell trait Laboratory findings:
Normal RBC morphology, with the exception of a few target cells
Laboratory diagnosis: sickle cell
Sickling Test
Solubility Test
sodium metabisulfite
Principle: addition of sodium metabisulfite enhances deoxygenation and sickling of the red blood cell
Specimen: Whole blood (EDTA/heparin)
Positive result: Sickling of cells
Sickling Test
sodium dithionite
- most common screening test for Hb S
Principle: addition of sodium hydrosulfite (dithionite) results to immediate lysis of RBC due to saponin and
reduction of of iron to its ferric state.
Specimen: Whole blood (EDTA/heparin/sodium citrate) Positive result: Turbidity
Solubility Test
defined by the structural formula Ξ±2B26GluβVal, which indicates that on the Ξ² chain at position 6, glutamic acid is replaced by valine
Hb SS
- defined by the structural formula Ξ±2Ξ²2 6 GluβLys, in which lysine is substituted for glutamic acid in position 6 of the Ξ² chain
HEMOGLOBIN C DISEASES
-polymers form a short, thick crystal within the RBCs (does not alter RBC shape to the extent that Hb S does)
- VOC Vasoocclusive crisis does not occur
- yields a negative result on the hemoglobin solubility test
HEMOGLOBIN C DISEASES
Double substitution on the Ξ² chain
(substitution of valine for glutamic acid at position 6 of the Ξ² chain, and the substitution at position 73 of aspartic acid for asparagine)
Hb C Harlem/Hb C Georgetown
Double mutation in the same beta chain
π©ΈBeta 6 Glutamic to valine
π©Έat position 73 of aspartic acid for asparagine
Hb C Harlem/Hb C Georgetown
Lysine is substituted for glutamic acid in position 26
(Hb EE resembles thalassemia trait)
Hb E
Substitution of lysine for glutamic acid at amino acid position 121
Hb O-Arab
2 substitution of a tyrosine for either proximal or distal histidine
Hb M
Double substitution glutamic to lysine and glutamic to valine
Not same beta mutation
Hb SC
