Transmission/disequilibrium tests for quantitative traits

The transmission/disequilibrium test (TDT) is a powerful method of locating disease genes. The TDT was originally proposed for use in studies of quali tative traits in families with both parents available. Recently, the TDT ha s been extended to studies of qualitative traits in sibships without parent s available and in families with one parent available. It has also been ext ended for use in studies of quantitative traits in families with both paren ts available and in sibships with multiple offspring. In this paper, we fir st propose a new class of TDT-type tests for linkage in the presence of lin kage disequilibrium for use in studies of families with both parents availa ble. The TDT of Spielman et al. (1993) for qualitative traits and the TDT o f Rabiaowitz (1997) for quantitative traits are special cases of the new te sts. Second, we propose a new class of TDT-type tests for linkage for use i n studies of families with one parent available. Third, we study the validi ty and the power of the tests using simulations. Finally, we propose a meth od of combining data from different types of families. The combined test is valuable and allows researchers full use of the available data in detectin g linkage between a marker locus and an unobservable quantitative trait loc us. An important feature of the tests proposed in this paper is that no ass umptions on the distribution of the quantitative traits are needed.