QUESTION 23
A 2-year-old male is being seen by his primary care physician in a small rural community. He was delivered at 38 weeks estimated gestational age and was healthy for several months after birth; however, at the age of 7 months, he developed a bad pneumonia, and cultures grew Streptococcus pneumoniae. At the age of 15 months, he developed a second pneumonia with the same organism. His current visit is for follow-up after his recent discharge from the hospital after an enteroviral encephalitis, which he barely survived. Laboratory testing reveals very low levels of immunoglobulins, including IgA, IgG, and IgM, and flow cytometry reveals no B cells in the blood. A mutation of the gene for which of the following types of proteins is responsible for his condition?
A. Guanine cyclase
B. GTPase
C. Tyrosine kinase
D. Choline kinase
E. Adenylate cyclase
Answer for Question 23
Answer: C (Tyrosine kinase)
Explanation: patients with X-linked agammaglobulinemia will present after the age of 6 months with recurrent infections, including with Streptococcus pneumoniae, Haemophilus influenzae, and enteroviruses, which are acquired through the gastrointestinal tract. Laboratory testing will reveal very low concentrations of the immunoglobulins and very low levels or absence of B cells in the blood. X-linked agammaglobulinemia is due to lack of Bruton’s tyrosine kinase, the loss of which inhibits the production of light chains, and subsequently the production of intact immunoglobulins. Heavy chains are still produced.
QUESTION 24
An 18-year-old male has had several episodes of sinusitis and a few episodes of significant diarrhea during his life. On a check-up with his new physician, his physician decides to order laboratory tests to investigate. Normal levels of IgG and IgM are found on testing, but his IgA is low. Of the following, which disease process is this patient at the greatest risk for developing?
A. Gallstones
B. Mycobacterium tuberculosis pneumonia
C. Hyperlipidemia
D. Chronic obstructive pulmonary disease
E. Rheumatoid arthritis
Answer for Question 24
Answer: E (rheumatoid arthritis)
Explanation: the history of recurrent sinus and gastrointestinal infections, and the laboratory test results, are consistent with a diagnosis of selective IgA deficiency, which presents after the age of 4 years, but can be asymptomatic also. These patients are at increased risk for allergies and the development of autoimmune disorders, which would include rheumatoid arthritis.
QUESTION 25
A 12-year-old female has had several severe episodes of diarrhea during her lifetime, and has had recurrent sinusitis and two episodes of pneumonia. Laboratory testing is most likely to reveal which of the following?
Answer for Question 25
Answer: B
Explanation: recurrent episodes of diarrhea and sinopulmonary infections first diagnosed in an older child are consistent with a selective IgA deficiency. Laboratory testing would reveal normal concentrations of IgG and IgM and normal number of T cells.