SCA/Thalassemias

Question 1

SCA-genetics

Answer 1

autosomal recessive, need two HbbS alleles to have disease

-glutamic acid in hemoglobin B-globin gene replaced with a valine due to SNP (A to T)

Question 2

SCA-carrier phenotype

Answer 2

-malaria resistant, but can have sickle crisis when deprived of oxygen or severely dehydrated

Question 3

SCA carrier prevalence

Answer 3

1:12 blacks/African Americans

Question 4

SCA disease prevalence

Answer 4

1: 365 black/African American births
1: 16,300 Hispanic American births

Question 5

SCA-pathology

Answer 5

• hemoglobin is improperly shaped, so red blood cells sickle when oxygen levels are low, leading to vessel occlusion and ischaemia
• sickled cells only last 10-20 days instead of 90-120 days in normal RBCs

Question 6

SCA-treatment

Answer 6

• prophylatic antibiotics
• hydroxyurea to increase fetal hemoglobin levels (normally this drops off by 6m of age, but its persistence can help with symptoms)
• blood transfusions
• pain meds
• bone marrow transplant (from sibling) can be curative

Question 7

SCA-diagnosis and screening

Answer 7

• genetic testing and blood sample (look at RBCS)

- some states do newborn screening

Question 8

B-0 thalessemia-describe

Answer 8

• absent synthesis of Beta chains of hemoglobin (homozygous recessive genotype) results in microcytic anemia (no adult hemoglobin)
• requires frequent blood transfusions and chelation (transfusion-caused iron overload)

Question 9

B+ thalessemia- describe

Answer 9

• heterozygous genotype, reduced beta chain expression so adult hemoglobin levels are reduced
• anemia still results but less severe