Is this particular leukemia absolutely associated with mutation in single gene of your interest?? it is possible that along with your gene of interest, mutation or dysfunction of one or few other genes may be involved.

Neeraja made a great point!  It is quite well-known  that methylation processes are involved in tumoral processes. Nevertheless, as stated by Smith et al, 2015 (link below)  for CLL, methylation is deregulation is key to disease progression but not necessarily for the onset of the disease. Probably some (one or several) driver mutations are required beforehand. Has your mutation of interest been described as a driver for the leukemia you are interested in?

http://www.nature.com/bcj/journal/v5/n4/full/bcj201514a.html

Hi Neeraja and Daniel,

Thanks for your reply. It is a particular type of leukemia but nothing is specified stating whether this mutation is an absolute necessary or sole factor responsible for the disease.The mutation is not described as a driver mutation. It only says that cloning of the mutated gene in normal bone marrow cells affect DNA methylation only but does not cause leukemia.

Hi Tanima,

I want to point out that there are several genes involved in regulating DNA methylation. Altering one gene and seeing some particular DNA methylation changes but not leukemia doesn't mean that DNA methylation and leukemia aren't related! There are other specific changes to DNA methylation that may occur when other DNA methylation genes are mutated or lost, which may lead to leukemia. 

As Neeraja and Daniel have pointed out, other mutations might be required before or after the mutation you are describing to cause leukemia. Also, if the result you are describing is using a mouse model, there are many factors that can affect whether the mouse gets leukemia - for example, a competitive transplant vs. non-competitive transplant changes whether knock-out of Dnmt3a in bone marrow leads to leukemia in mice (see: Challen et al Nature Genetics 2011 - PMID:22138693 vs. Mayle et al and Celik et al, both in Blood 2015 PMID: 25416277, 25416276).