Alterations in the ratio of CD4:CD8 lymphocytes are associated with risk of HIV infection progressing to AIDS, of autoimmune diseases, and of progression of some cancers. In searching for predictors of these effects in normal individuals, researchers have found two independent QTLs in the region of the genome known as the major histocompatibility complex (MHC), one in a region regulating CD8 and the other in a region regulating CD4. What does this indicate for the general population?
A)Mutation in one or both of these genes causes HIV and AIDS.
B)Autoimmune diseases such as type 1 diabetes are caused by one of these genes.
C)Variation in linkage disequilibrium with one or both of these mutations may increase the risk of autoimmune disease.
D)Only one mutation can be the cause of rheumatoid arthritis.
E)The probability of an autoimmune disease demonstrates that additive genes are involved.

Question

Quizplus · Accepted Answer

The presence of two independent QTLs in the MHC region suggests that variation in linkage disequilibrium with one or both of these mutations may increase the risk of autoimmune disease, rather than causing the disease itself. This indicates that additive genes are involved, and that the ratio of CD4:CD8 lymphocytes is a complex trait influenced by multiple genetic factors.

Alterations in the Ratio of CD4:CD8 Lymphocytes Are Associated with Risk