Test for decrease in age at diagnosis of lynch syndrome over successive generations

He, Yanjing (2011) Test for decrease in age at diagnosis of lynch syndrome over successive generations. Masters thesis, Memorial University of Newfoundland.

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Abstract

The study of age at onset anticipation and parent-of-origin effects on age at onset in Lynch Syndrome (LS) are of interest to both clinical medicine and research. Although several studies have suggested the presence of age at onset anticipation and parent-of-origin effects on age at onset of LS, the question remains as to whether this evidence reflects ascertainment bias rather than the phenomenon under study. The aim of this thesis is to assess decrease in age at diagnosis of LS over successive generations as well as parent-of-origin effects on age at diagnosis of LS based on the data provided by the Colon Cancer Family Registry. We first demonstrate that the variable age at diagnosis in the sample is right truncated by the closing date of the study and, as a result, the variable age at diagnosis is a biased sample of the target populations. To assess decrease in age at diagnosis of the disease over successive generations, we use the symmetry test proposed by Tsai et al. (2005) which accounts for the bias caused by the right truncation of both the parent's and child's ages at diagnosis. To test parent-of-origin effect, we examine and improve the method used by Lindor et al. (2010). Based on our preliminary analysis, we did not find sufficient statistical evidence from this sample to claim that there exists a parent-of-origin effect on age at diagnosis of LS relating to either the gender of the parent or the gender of the offspring after accounting for the sampling bias. The results given by the symmetry test suggest that there exists a decrease in age at diagnosis of LS over successive generations. This result should be free of the sampling bias caused by the right truncation. What remains uncertain is whether true genetic anticipation contributes to the decrease in age at diagnosis over successive generations observed in this disease.

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