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