QUESTION 17
A 10-month-old male is being seen by his pediatrician for follow-up. Over the past three months, he has twice had pneumonia, once with Streptococcus pneumoniae and once with Haemophilus influenzae. His mother is very concerned, as he was perfectly healthy up to around the age of 6 months, and ever since has seemed to just get sick. Laboratory testing reveals essentially no IgG or IgA in the blood. Flow cytometry reveals an absence of CD19+ cells. Of the following, what is the pattern of inheritance of this disease process?
A. Autosomal dominant
B. Autosomal recessive
C. X-linked
D. Y-linked
E. Mitochondrial
Answer for Question 17
Answer: C (X-linked)
Explanation: the development of recurrent pulmonary infections with encapsulated organisms in a male greater than 6 months of age is consistent with Bruton’s agammaglobulinemia. The essential absence of two or more types of Ig and the absence of B cells by flow cytometry, as confirmed by the absence of CD19+ cells (CD19 is a B cell marker), confirms the diagnosis. Bruton’s agammaglobulinemia is X-linked, and, thus, present in males. As the presence of mother’s antibodies protects the infant for a time period after birth, this disease usually presents after the age of 6 months.
QUESTION 18
A 6-year-old male has had several skin infections during his childhood with some requiring drainage. He also has had three episodes of pneumonia and one episode of cystitis that caused obstruction. In each case either Staphylococcus aureus or Escherichia coli were cultured. His parents have brought him to an acute care clinic, because he is febrile and appears slightly jaundiced to them. A CT scan reveals punctate lesions in the liver and lungs. A biopsy of his liver reveals numerous non-caseating granulomas. Of the following, a mutation of the gene for which of the following proteins is responsible for his underlying condition?
A. An integrin
B. IL-1
C. Phagocyte oxidase
D. LYST
E. PECAM
Answer for Question 18
Answer: C (phagocyte oxidase)
Explanation: the patient has chronic granulomatous disease, which is most commonly X-linked and thus presents in males, usually in early childhood. Patients develop granulomas, because the defective phagocyte oxidase does not allow them to produce reactive oxygen species, such as superoxide radical, and thus their ability to kill bacteria is diminished. Instead, the body’s macrophages respond and wall off the infections, creating granulomas. Integrin defects (Leukocyte adhesion deficiency) and LYST defects (Chediak-Higashi syndrome) are not commonly associated with the formation of granulomas.
QUESTION 19
A 4-year-old male who normally has a decreased pigmentation of his skin and has had several episodes of pneumonia and three skin infections, all bacterial in origin, during his lifetime, is brought to the emergency room by his parents because his skin has turned yellow, he was not feeding well, and has stopped talking, and he has a fever. Physical examination reveals an enlarged liver and spleen and prominent lymph nodes. A peripheral smear of his blood reveals neutrophils containing large granules. Of the following, what is the mechanism of his disease process?
A. Failure of white blood cells to bind to integrins
B. Failure of white blood cells to transmigrate
C. Decreased production of oxygen-derived free radicals
D. Abnormal fusion of phagosomes and lysosomes
E. Failure of DNA repair
ANSWER for Question 19
Answer: D (abnormal fusion of phagosomes and lysosomes)
Explanation: the albinism and recurrent bacterial infections are consistent with Chediak-Higashi syndrome. Patients with Chediak-Higashi syndrome can enter an accelerated phase, which can include jaundice, neurological changes, fever, hepatosplenomegaly, and lymphoadenopathy. Chediak-Higashi is autosomal recessive involving the LYST gene, which produces a protein that plays a role in lysosomal trafficking, resulting in abnormal fusion of phagosomes and lysosomes. Patients can have enlarged granules in the cytoplasm of neutrophils, which represent the abnormal fusion of the phagosome and the lysosome.