Abstract
Two issues regarding the robustness of the original transmission disequilibrium test (TDT) developed by Spielman et al are: (i) missing parental genotype data and (ii) the presence of undetected genotype errors. While extensions of the TDT that are robust to items (i) and (ii) have been developed, there is to date no single TDT statistic that is robust to both for general pedigrees. We present here a likelihood method, the TDTae, which is robust to these issues in general pedigrees. The TDTae assumes a more general disease model than the traditional TDT, which assumes a multiplicative inheritance model for genotypic relative risk. Our model is based on Weinberg's work. To assess robustness, we perform simulations. Also, we apply our method to two data sets from actual diseases: psoriasis and sitosterolemia. Maximization under alternative and null hypotheses is performed using Powell's method. Results of our simulations indicate that our method maintains correct type I error rates at the 1, 5, and 10% levels of significance. Furthermore, a Kolmorogov–Smirnoff Goodness of Fit test suggests that the data are drawn from a central χ2 with 2 df, the correct asymptotic null distribution. The psoriasis results suggest two loci as being significantly linked to the disease, even in the presence of genotyping errors and missing data, and the sitosterolemia results show a P-value of 1.5 × 10−9 for the marker locus nearest to the sitosterolemia disease genes. We have developed software to perform TDTae calculations, which may be accessed from our ftp site.
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Acknowledgements
We gratefully acknowledge grants K01-HG00055 and R01-MH59492 from the National Institutes of Health. Also, we thank Dr Shailesh Patel for thoughtfully providing data from his sitosterolemia study. The psoriasis study is funded in part by NIH grant AR049049. Last but not least, we thank three anonymous reviewers whose comments greatly improved earlier versions of the manuscript. The sitosterolemia study is funded in part by grant NIH NHLBI HL 060613
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Appendix A
Appendix A
The following notation will be used through the entire Materials and methods and Results section of this work. We place it here to improve ‘flow’ of the text.
Marker alleles
All alleles will be coded numerically. Unless otherwise stated, it is assumed that all markers are di-allelic, with allele codings ‘1’ and ‘2’.
Genotype parameters

(For a discussion about this choice of parameters vs Weinberg et al's ‘Mating Type’ parameters, see Discussion.)
Error model parameters

When discussing an arbitrary error model, we will use the vector notation to indicate the set of error model parameters. For example,
when the error model is DSB, and
when the error model is SPL. The symbol
may also be used to represent a given error model, since (as mentioned above) an error model is completely determined by its parameters. We shall use this equivalence from this point forward.
Penetrances

where ‘+’ refers to a wild-type or low-risk allele at a disease locus, and ‘d’.
Genotypic relative risks

Likelihood Equation Terms
=Pr (observed genotype=i ∣ true genotype=j) for error model
(also known as the penetrance function)

(the genotype frequency function for the genotype i).
Pedigree identification
Let a represent an ID for an individual in a pedigree (usually a positive integer). Then,

Likelihood ratio statistic
For a parameter ξ in the likelihood

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Gordon, D., Haynes, C., Johnnidis, C. et al. A transmission disequilibrium test for general pedigrees that is robust to the presence of random genotyping errors and any number of untyped parents. Eur J Hum Genet 12, 752–761 (2004). https://doi.org/10.1038/sj.ejhg.5201219
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DOI: https://doi.org/10.1038/sj.ejhg.5201219
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