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Red and White Cells, Reticuloendothelial System—Hematology, Immunology

Questions

406. A 12-month-old girl presents for evaluation of extreme irritability without fever. She came to Texas shortly after birth as a Somalian refugee, and seemed to feed and grow well with a slight falloff in weight recently. Physical examination reveals a slightly enlarged liver, a palpable spleen, and tenderness over her extremities. A peripheral smear shows sickle-shaped red blood cells and subsequent studies confirm a diagnosis of sickle cell anemia (MIM*603903). When told this is a genetic disorder, the parents are skeptical because she had been so healthy early in life. Which of the following explanations concerning hemoglobin chain structure best explains her lack of symptoms the first few months after birth?

a. The (α₁-α₂)(β₁-β₂) subunit structure shifts to (α₁-β₁)-(α₂-β₂) at puberty

b. The α₁-α₂-α₃-α₄ subunit structure switches to (α₁-β₁)-(α₂-β₂) during pregnancy

c. β-β-β-α Subunit structure switches to (α₁-β₁)-(α₂-β₂) during infancy

d. The (β₁-β₂-β₃-α₁) subunit structure switches to (α₁-β₁)-(α₂-β₂) during pregnancy

e. The (α₁-γ₁)-(α₂-γ₂) subunit structure switches to (α₁-β₁)-(α₂-β₂) at 2 to 6 months.

407. A 2-year-old Hispanic boy presents with frequent sinus and ear infections, including one, which progressed to staphylococcal bacteria in the blood (bacteremia) and bone infection (osteomyelitis). Family history indicated that his mother had a brother who died young of sepsis and that her mother had two brothers who died young. Suspicion of an X-linked immunoglobulin deficiency led to assay for a phosphokinase that is known to be deficient in Bruton X-linked agammaglobulinemia (MIM*300300). Which of the following amino acids could be used as an acceptor for the phosphate group in the Bruton kinase assay?

a. Cysteine

b. Leucine

c. Methionine

d. Tyrosine

e. Tryptophan

408. A 17-year-old African American adolescent is evaluated for anemia and is found to have increased indirect bilirubin in serum and plasmafree hemoglobin suggestive of hemolysis (lysis of red blood cells). Enzyme assays reveal deficiency of bisphosphoglycerate mutase (MIM*222800) with low concentrations of 2,3-bisphosphoglycerate (BPG) in her red blood cells. The teenager shows greater respiratory distress than expected for the degree of anemia. Which of the following statements best explains the consequences of this enzyme deficiency?

a. BPG shifts the curve to the right, so less BPG will cause greater release of oxygen to tissues.

b. BPG shifts the curve to the right, so less BPG will cause lesser release of oxygen to tissues.

c. BPG shifts the curve to the left, so less BPG will cause greater release of oxygen to tissues.

d. BPG shifts the curve to the left, so less BPG will cause lesser release of oxygen to tissues.

e. BPG binds oxygen directly and has no effect on the curve.

409. An 18-year-old African American female is evaluated for her first prenatal visit and is found to have chronic anemia, a slightly enlarged spleen, increased reticulocyte count, and mild elevation of indirect-reacting (unconjugated) bilirubin in serum. Incubation of the female’s red cells with glucose yields decreased amounts of ATP as compared to controls, even in the presence of oxygen. The female’s anemia is explained by the fact that ATP is produced by which of the following pathways?

a. Glycogen breakdown

b. Glycolysis

c. Oxidative phosphorylation

d. Pentose phosphate cycle

e. Lactate conversion to glucose (Cori cycle)

410. A 25-year-old Nigerian medical student studying in the United States develops hemolytic anemia after taking the oxidizing antimalarial drug primaquine. Which of the following is the most likely cause of this severe reaction?

a. Glucose-6-phosphate dehydrogenase deficiency

b. Concomitant scurvy

c. Vitamin C deficiency

d. Diabetes

e. Glycogen phosphorylase deficiency

411. A 6-year-old boy of Lebanese origin with a past history of mild anemia becomes very ill after a wedding celebration, showing pallor, rapid heart rate, shortness of breath, and dark urine. Emergency room evaluation shows a hemoglobin of 5 g/dL (mean for age 13.5) with 11% reticulocytes (normal 0.5-1). Glucose-6-phosphate dehydrogenase deficiency (MIM*305900) is suspected, known to produce high levels of oxidized glutathione and hydrogen peroxide in red blood cells with consequent membrane damage, hemolysis, and anemia. Which of the following redox pairs, due to its high redox potential, is crucial for glutathione reduction?

a. Fumarate/succinate

b. NADP⁺/NADPH or NAD/NADH

c. Oxaloacetate/malate

d. Pyruvate/lactate

e. 6-Phosphogluconate/ribulose-5-phosphate

412. A 20-year-old Asian female is evaluated on her first prenatal visit and is found to have a hemoglobin of 10 g/dL (normal mean of 14). Prenatal vitamins with iron are prescribed but her anemia persists. Further evaluation shows an elevated reticulocyte count, and red cell enzyme levels are performed to find a cause for her hemolytic anemia. Partial deficiency of hexokinase (MIM*235700) is found, but the rare reports of this condition cause her physicians suspect an uncharacterized defect in red cell metabolism that depletes redox potential. This is because the conversion of glucose to glucose 6-phosphate requires coupling to ATP hydrolysis. Which of the following correctly explains the reason why?

a. The reaction has a positive free energy.

b. The reaction has a negative free energy.

c. Glucose 6-phosphate is unstable.

d. Glucose and other sugars are high-energy substrates.

e. Allosteric activation of hexokinase enzyme.

413. A 2-year-old Caucasian girl with chronic diarrhea and anemia is evaluated and found to have abetalipoproteinemia (MIM*200100), a disorder caused by defective transport and deficiency of the apoB protein. Which of the following classes of serum lipids would be expected to be deficient in abetalipoproteinemia?

a. Lipoprotein (a)

b. High-density lipoproteins (HDLs)

c. Chylomicrons

d. Triglycerides

e. Low-density lipoprotein receptor

414. Folic acid deficiency may present with megaloblastic anemia or be diagnosed by its effect on certain metabolic pathways. Which of the following amino acids and their catabolic products require folate along with an intermediate that, when elevated in serum, indicates folate deficiency?

a. Serine, glycine, and carbon dioxide

b. Cystine, cysteine, and mercaptopyruvate

c. Glycine, alanine, and pyruvate

d. Threonine, acetaldehyde, and acetate

e. Histidine, formiminoglutamate, and glutamate

415. Mothers taking warfarin for anticoagulation during pregnancy may have children with fetal warfarin syndrome involving very short nose and skeletal changes. Studies of the actions of the anticoagulants dicumarol and warfarin (the latter also a hemorrhagic rat poison) have revealed which of the following?

a. Vitamin C is necessary for the synthesis of fibrinogen.

b. Vitamin C activates fibrinogen.

c. Vitamin K is a clotting factor.

d. Vitamin K is essential for γ-carboxylation of glutamate.

e. The action of vitamin E is antagonized by these compounds.

416. A 10-day-old male Sudanese infant is evaluated in a refugee camp and found to have large areas of bruising on the skin (purpura) with oozing of blood from his umbilicus. Which of the following statements best describes his likely vitamin deficiency and its mechanism?

a. The vitamin is broken down by intestinal bacteria and facilitates synthesis of clotting factors.

b. The vitamin is antagonized by heparin and facilitates glycosylation of clotting factors.

c. The vitamin is obtained by eating egg yolk and liver but not green vegetables.

d. The vitamin is antagonized by a rat poison, is active in glutamate carboxylation, and facilitates calcium chelation.

e. The vitamin was discovered by studying hemorrhagic disease of the newborn.

417. The major blood group locus in humans produces types A (genotypes AA or AO), B (genotypes BB or BO), AB (genotype AB), or O (genotype OO). For parents who are type AB and type O, what are the possible blood types of their offspring?

a. Type AB child

b. Type B child

c. Type O child

d. Type A or B child

e. Type B or AB child

418. Increased resistance to malaria is seen in persons with hemoglobin AS, where A is the normal allele and S is the allele for sickle hemoglobin. Which of the following terms applies to this situation?

a. Founder effect

b. Heterozygote advantage

c. Genetic lethal

d. Fitness

e. Natural selection

419. Assume that frequencies for the different blood group alleles are as follows: A = 0.3; B = 0.1; and O = 0.6. What is the expected percentage of individuals with blood type B?

a. 7%

b. 13%

c. 27%

d. 36%

e. 45%

420. An African American couple with a normal family history want to know their chance of having a child with sickle cell anemia (MIM*603903). The incidence of sickle cell trait is 1 in 8 for African Americans. Which of the following is the risk in this case?

a. ¹/8

b. ¹/16

c. ¹/60

d. ¹/120

e. ¹/256

421. The parents of a girl with Tay-Sachs disease (MIM*272800) decide to pursue bone marrow transplantation in an attempt to provide a source for the missing lysosomal enzyme. Preliminary testing of the girl’s normal siblings is performed to assess their carrier status and their human leukocyte antigen (HLA) locus compatibility with their affected sister. What is the chance that one of the three siblings is homozygous normal (ie, has a good supply of enzyme) and HLA-compatible?

a. ½

b. ¹/3

c. ¼

d. ¹/6

e. ¹/12

422. A sibling donor is found for a patient with Tay-Sachs disease (MIM*272800), and the physician writes to the patient’s insurance company explaining the diagnosis of Tay-Sachs disease and the reasons for the bone marrow transplant. Not only does the insurance company refuse payment for transplantation, it also discontinues coverage for the family based on anticipated medical expenses. From the ethical perspective, these events fall under which of the following categories?

a. Patient confidentiality

b. Nondisclosure

c. Informed consent

d. Failure to provide ongoing care

e. Discrimination

423. A female presents with fatigue, pallor, and pale conjunctival blood vessels. She gives a recent history of metrorrhagia (heavy menstrual periods). Which of the following laboratory findings is most likely?

a. High serum haptoglobin

b. High serum iron

c. High numbers of transferrin receptors

d. High saturation of transferrin

e. High serum ferritin

424. Screening of an African American population in Minnesota yields allele frequencies of ⁷/8 for the A globin allele and ¹/8 for the sickle globin allele. A companion survey of 6400 of these people’s ancestors in central Africa reveals 4600 individuals with genotype AA, 1600 with genotype AS (sickle trait), and 200 with genotype SS (sickle cell disease—MIM*603903). Compared to their descendants in Minnesota, the African population has which of the following?

a. A lower frequency of AS genotypes consistent with inbreeding

b. A lower frequency of AS genotypes consistent with malarial exposure

c. A higher frequency of AS genotypes consistent with heterozygote advantage

d. A higher frequency of AS genotypes consistent with selection against the S allele

e. Identical A and S allele frequencies as predicted by the Hardy-Weinberg law

425. A prominent chemist once suggested that individuals who carry or are affected with sickle cell anemia (MIM*603903) have tattoos on their foreheads so they will avoid mating, thus eliminating the disease from the population. If all SS individuals in a population were counseled to avoid reproducing naturally, the SS genotype frequency in the next generation would be which of the following?

a. Reduced by ²/3

b. Reduced by ½

c. Reduced by ¹/3

d. Reduced to 0

e. Approximately the same

426. A female who has two brothers with hemophilia A (MIM*306700) and two normal sons is again pregnant. She requests counseling for the risk of her fetus to have hemophilia. What is the risk that her next child will have hemophilia?

a. 1

b. ½

c. ¼

d. ¹/8

e. ¹/16

427. Which of the following statements best describes hemophilia A (MIM*306700)?

a. The extrinsic clotting pathway is impaired.

b. The cleavage of fibrinogen is impaired.

c. Tissue factor activation is impaired.

d. Activation of factor XII is impaired.

e. Activation of factor X is impaired.

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