The Lancet has an article in the current issue titled Epigenetic differences between Wilms' tumours in white and east-Asian children (free registration not worth it). Here is a press article on the study. I haven't read the full journal article, but it seems that the gene in European children is causing the problem:

...showed that a gene produced an excessive amount of growth in about half the cases involving European children.

"Surprisingly this mechanism is absent in Asians, accounting for why the population has one half the rate of this disease than Caucasians...