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Correspondence  |   July 2007
Basic Genetic Statistics Are Necessary in Studies of Functional Associations in Anesthesiology
Author Notes
  • (Accepted for publication February 19, 2007.)
    (Accepted for publication February 19, 2007.)×
Article Information
Correspondence
Correspondence   |   July 2007
Basic Genetic Statistics Are Necessary in Studies of Functional Associations in Anesthesiology
Anesthesiology 7 2007, Vol.107, 169. doi:10.1097/01.anes.0000268547.73216.ec
Anesthesiology 7 2007, Vol.107, 169. doi:10.1097/01.anes.0000268547.73216.ec
In Reply:—
We thank Dr. Lötsch for his comments regarding our work.1  Strictly speaking, his comments for the Hardy-Weinberg equilibrium are correct, but they may not apply to our study. For the Hardy-Weinberg equations to apply, several conditions must be met. No mutations can be occurring, no natural selection pressures must be operating, the population of interest is infinitely large, all members of the population must breed and mating is totally random, and there must be no in or out migration of the populations.*1  There are several situations in regard to our study sample that may violate one or more of these conditions.
First, we worked with a “convenience” (nonrandom), small (80-subject) sample. Because these were surgical patients (and only women), this sample may not be representative of the “infinite population.”
Second, because our patients were drawn from a limited geographic area, they may not be representative of the population as a whole. We cannot exclude the possibility that inbreeding (or in/out migration) may have occurred; in small human groups, such factors cannot be controlled nor easily identified.
Third, the locus of interest is autosomal (males and females have similar allele frequency).
Fourth, because we know so little about the evolutionary impact of these alleles, it is impossible to know whether evolutionary pressures exist within our population or our sample. It is entirely possible that different genotypes in the human opioid receptor A118G polymorphism may convey different degrees of “evolutionary fitness.”
If the assumptions underlying the Hardy-Weinberg equilibrium are violated, statistical methods using allele frequencies may not be valid, and methods that use genotype frequencies should be preferred.2 
In summary, although we thank Dr. Lötsch for his thoughtful comments, we do not believe that they invalidate the basic observations contained in our study.
Wen-Ying Chou, M.D.,† Ping-Hsin Liu, M.D. Chien-Cheng Liu, M.D. Chia-Chih Tseng, M.D. Bruno Jawan, M.D. †Chang Gung Memorial Hospital–Kaohsiung Medical Center, Chang Gung University College of Medicine, Taiwan. wych@ms21.hinet.net
References
Chou, W-Y, Wang, C-H, Liu, P-H, Liu, C-C, Tseng, C-C, Jawan, B The human opioid receptor A118G polymorphism affects intravenous patient-controlled analgesia morphine consumption after total abdominal hysterectomy.. Anesthesiology. (2006). 105 334–7 [Article] [PubMed]
Xu, J, Turner, A, Little, J, Bleecker, ER Positive results in association studies are associated with departure from Hardy-Weinberg equilibrium: Hint for genotyping error?. Hum Genet. (2002). 111 573–4 [Article] [PubMed]
* Dorak MT: Basic population genetics. Available at: http://www.dorak.info/genetics/popgen.html. Accessed April 2, 2007.
* Dorak MT: Basic population genetics. Available at: http://www.dorak.info/genetics/popgen.html. Accessed April 2, 2007.×