QTDT - Background Information

How is association mapping going to help me find genes?

During the past decade, the genes for a large number of rare mendelian traits have been identified. However, traditional linkage analyses lack power and precision when applied to complex disease. Association mapping, which compares the effects of different chromosomal variants, may be more successful at identifying genes of small effect.

How does QTDT help association mapping?

Association mapping can produce misleading results when the study population is not homogeneous, but includes individuals with different genetic backgrounds. Family based association tests, commonly referred to as TDTs (Transmission Disequilibrium Tests), do not produce misleading results in these circumstances. QTDT can use all the information in a pedigree to construct powerful tests of association that are robust in the presence of stratification.

What does the Q stant for ?

Q stands for Quantitative. Quantitative traits provide effective descriptions of many complex diseases, including asthma. For many of these conditions, all or nothing definitions of disease are arbitrary and unsatisfactory. QTDT incorporates variance components methodology in the analysis of family data and includes exact estimation of p-values for analysis of small samples and non-normal data. The QTDT abbreviation (for Quantitative Transmission Disequilibrium Tests) was first used by David Allison in his 1997 paper.