Case 1

Published on 18/02/2015 by admin

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Last modified 18/02/2015

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CASE 1

Mark is a 7-month-old boy who was born at term (40 weeks) weighing 4 kg, physically normal and apparently healthy. Although Mark was well the first couple of months of life, the last 3 months have shattered the illusion that Mark is healthy and normal. In the last few months, Mark has been plagued with fungal (diaper rash, oral candidiasis), viral (upper respiratory tract infections), and bacterial (otitis media) infections, all of which resolved with appropriate pharmacologic intervention. Mark has received routine childhood immunization, which his mother hoped would reduce the number of infections. Not surprising, Mark has not thrived and is well below the 50% percentile for weight. Mark was referred to a pediatrician who noted that Mark had (once again) a diaper rash and candidiasis (Fig. 1-1) and an upper respiratory tract infection. Despite these infections, his tonsils and lymph nodes were barely detectable. The pediatrician ordered a number of tests that included a complete blood cell count with differential, serum immunoglobulin (IgG), and a chest radiograph. The blood cell count indicated a low leukocyte count, profound lymphopenia, and very low serum IgG value.

FIGURE 1-1 Severe disseminated candidal infection (A) on the trunk, (B) in the mouth, and (C) on the nails of a child.

(From Fireman P, Slavin R: Atlas of Allergies, 2nd ed. St. Louis, Mosby, 1996.)

QUESTIONS FOR GROUP DISCUSSION

1. When taking a family history, why is it important to determine whether both male and female members of the family have been affected?

2. This patient has a history of infection with bacteria, viruses, and fungi. What lymphoid defect is suggested when a patient has a history of bacterial infection? What lymphoid defect is suggested when a patient has a history of viral and fungal infections?

3. With what type of infection history would a patient with a myeloid progenitor cell defect present?

4. What is the rationale for requesting a complete blood cell count with differential? Given the information presented in this case, what would you expect a blood test to reveal?

5. A history of bacterial, viral, and fungal infections suggests that both T cell and B cell function are affected. What laboratory technique is used to determine the relative numbers of B cells and T cells in circulation?

6. What is the significance of small tonsils and barely detectable lymph nodes? This could have been predicted given the very low levels of serum immunoglobulin. Explain.

7. How can the fact that this child has been immunized be used to determine if B cell function is intact?

8. NK cells are also derived from a lymphoid stem cell. What cell surface marker can be used to quantitate circulating NK cells by flow cytometry? What type(s) of infections would a patient have if he or she had a deficiency of NK cells?

9. On the basis of the listed tests, the patient was shown to have a defect in T cells, B cells, and NK cells, suggesting a defect at the level of a lymphoid progenitor cell. Such defects give rise to severe combined immunodeficiency disorder (SCID). There are several mutations or defects that can give rise to SCID. Explain how mutations or defects in each of the following would result in SCID phenotype: (a) adenosine deaminase; (b) CD132-γ common chain present in several cytokine receptors, (c) recombinase activating genes RAG1 and RAG2; and (d) JAK 3.

10. Describe potential therapeutic interventions.

RECOMMENDED APPROACH

Implications/Analysis of Family History

Immunodeficiency disorders present as recurrent and persistent infections. Because these disorders may be inherited or acquired, a family history indicating that other members have been affected similarly would indicate a genetic basis for the infections. A history indicating that only male infants have been affected directs the physician toward a defect in a gene encoded on the X chromosome. Genetic defects in which both male and female family members are also affected generally indicate an autosomal recessive mode of inheritance. In this particular case, Mark’s family history indicated that both sexes have been affected and so the cause of these infections is unlikely to be an X-linked disorder.

Implications/Analysis of Clinical History

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