As your authors point-out, some HLA alleles occur at a much higher frequency in

Question

As your authors point-out, some HLA alleles occur at a much higher frequency in some people suffering from certain diseases than are found in the general population. The diseases associated with certain MHC alleles include: certain autoimmune disorders; certain viral diseases; disorders of the complement system; some neurological disorders; and, several, different allergies. In humans, the association between an HLA allele and a given disease can be quantified by determining the frequency of that allele expressed by individuals afflicted with the disease as compared to the frequency of the same allele in the general population. Such a comparison allows for the calculation of an individual's relative risk (RR); or, RR=frequency disease in the allele+ group/frequency of disease in the allele- group, So, an RR of 1 would mean that the HLA allele in question is expressed with the same frequency in the disease-afflicted as it is expressed in the general population. Therefore, for example, the crippling autoimmune spinal disease , Ankylosing spondylitis (As), has an RR of 87.4 for the Class I, HLA-B27 allele. Do you think, then, for this disorder (As) that a high RR, as in the case of Ankylosing spondylitis, indicates that the disease is a phenotypic expression of the patient's genotype, or that it indicates a much higher predisposition for the expression of the disorder? Provide support for your answer.

Explanation / Answer

Relative risk ,as the name indicates gives the amount of risk more in the exposed group than the non exposed group.Therefore RR of 1 means that there is no additional risk ,RR less than 1 means that the exposure is protective to the person ,And Re of more than 1 means that the situation/exposure is harmful to the patient

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