Tests and estimates of allelic association in complex inheritance.
Family-based procedures such as the transmission disequilibrium test (TDT) were motivated by concern that sample-based methods to map disease genes by allelic association are not robust to population stratification, migration, and admixture. Other factors to consider in designing a study of allelic association are specification of gene action in a weakly parametric model, efficiency, diagnostic reliability for hypernormal individuals, interest in linkage and imprinting, and sibship composition. Family-based samples lend themselves to the TDT despite its inefficiency compared with cases and unrelated normal controls. The TDT has an efficiency of 1/2 for parent-offspring pairs and 2/3 for father-mother-child trios. Against cases and hypernormal controls, the efficiency is only 1/6 on the null hypothesis. Although dependent on marker gene frequency and other factors, efficiency for hypernormal controls is always greater than for random controls. Efficiency of the TDT is increased in multiplex families and by inclusion of normal sibs, approaching a case-control design with normal but not hypernormal controls. Isolated cases favor unrelated controls, and only in exceptional populations would avoidance of stratification justify a family-based design to map disease genes by allelic association.
Morton
N E
NE
Human Genetics, University of Southampton, Level G, Princess Anne Hospital, Coxford Road, Southampton SO16 5YA, United Kingdom. nem@soton.ac.uk
Collins
A
A
D000483:Alleles; D016022:Case-Control Studies; D002874:Chromosome Mapping; D003922:Diabetes Mellitus, Type 1 / Q000235:genetics; D005190:Family; D005260:Female; D030342:Genetic Diseases, Inborn / Q000235:genetics*; D008040:Genetic Linkage / Q000235:genetics; D005819:Genetic Markers / Q000235:genetics; D005823:Genetics / Q000706:statistics & numerical data; D006801:Humans; D008297:Male
D005819:Genetic Markers