Multiple Choice Questions

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Chapter 9, Question 1.


1. Two young siblings present with recurrent and severe viral infections. Surface expression of MHC class II on their cells is normal but surface expression of MHC class I is virtually absent. Staining of the lymphocytes shows cytoplasmic expression for MHC class I antigens. It is noted that they express the same HLA class II allotypes, suggesting that they inherited the same HLA gene complex from each parent. Other, unaffected siblings express different MHC class II molecules or partially overlapping allotypes. Both parents are normal and express class I antigens from each of the two chromosomes where class I genes are located. Based on the clinical presentation, test results, and inheritance pattern, you surmise which of the following?

a. There is a dominant mutation in the HLA class I genes on chromosome 6.

b. There is a recessive mutation in the HLA class I genes on chromosome 6.

c. There is a mutation in the gene for the β2microglobulin molecule.

d. There is a dominant mutation in the gene for Tap 1 and Tap 2.

e. There is a recessive mutation in the gene for Tap 1 and Tap 2.