I am planning to use association tests such as burden test, but I only have a few sample size. Are there any papers/references, beside this guide ( http://faculty.washington.edu/tathornt/SISG2015/lectures/Taipei2015/Taipei2015session07.pdf ), that would tell how many samples I need to achieve certain power (or the minimum number of samples). I know there are some papers that discuss about the power calculation using at least 500 samples, but I need something for sample size below 50.

Thanks, but when you say effects size or odds ratio, do you mean the minor allele frequency? How could we correlate MAF with odds ratio?