Читать книгу The Statistical Analysis of Doubly Truncated Data - Prof Jacobo de Uña-Álvarez, Prof Carla Moreira - Страница 22

Clark et al. (2011) investigated the association of candidate single nucleotide polymorphisms (SNPs) and age of onset of Parkinson's disease (PD). For this, genomic DNA samples from human blood samples were obtained from the National Institute of Neurological Disorders and Stroke (NINDS) Human Genetics DNA and Cell Line Repository at the Coriell Institute for Medical Research (Camden, New Jersey). More specifically, one aim of the study was to detect association between the rs8192678 PGC‐1a and A10398G SNPs and the risk or age of onset of PD.

Table 1.5 Parkinson's Disease Data: age of onset for genetic groups. Early onset: 35–55 years; late onset: 63–87 years. Sample size and mean (and standard deviation, SD) for the age of onset (years).

Group	SNP	Alleles		Mean (SD)
Early onset	A10398G	A	76	46.93
		G	21	47.14
	PGC‐1a	A	8	50.00
		AG	50	47.18
		G	39	46.10
Late onset	A10398G	A	73
		G	27	75.33
	PGC‐1a	A	10	74.00
		AG	37	76.49
		G	53	74.49

In order to remove the selection bias related to survival, the study was limited to patients diagnosed from PD who had their DNA sample taken within 8 years after onset. Consequently, the age of onset is right truncated by the age at blood sampling , and it is left truncated by (age in years). Clark et al. (2011) considered only the right‐truncation issue, but ignored left‐truncation. Both truncation limits were taken into account however in several re‐analyses of the PD data, including Austin et al. (2014) and Mandel et al. (2018).

Clark et al. (2011) divided the cases into an earlier age of onset group (35–55 years) with 99 patients, and a later age of onset group (63–87 years) with 100 patients. The genetic information of these cases, together with basic statistics on the age of onset, is reported in Table 1.5. The early onset group have two patients with missing data on A10398G SNP and on age at sampling, and these are excluded from the analysis.

The Parkinson's Disease Data are used in Chapters 2 and 4. Access to this dataset is possible through the DTDA package, which includes the data frames PDearly and PDlate, for the early and late onset groups, respectively.