I observed once in microarray analysis[Log fold change was really high].. But then found that I did something wrong in analysis.

I observed expression changes of some mRNAs in the range of several dozens to several 100-fold. This usually happens when a gene is *really* induced and was absent or at a very low level before.

Hi Bernardo

This is perfectly possible. For example this is a paper in which the authors claim a 60,000x fold increase of circulating miR-122 after cardiogenic shock in pigs. This is measured by qPCR.

http://www.ncbi.nlm.nih.gov/pubmed/22089187

By NGS I have already seen fold changes of 30x or 40x. So, I am not admired about your 200x fold. Just depends on getting the proper cell situation..

Best. Paco

It is possible. I've got high relative expression for one gene associated with plastid (chloroplast) genome (we expect this sequence is spread also in nuclear genome in high copy number). If all your controls, replicates,are ok. then it's fine.

There are some regulations of the kind on/off. This occur often in the case of microarray analysis particularly when a miRNA is not expressed in your control cells. This case is less common when the miRNA is stably expressed. Here you find a guideline with some examples of a good pipeline to check if you did correctly the analysis.

http://www.arraystar.com/supports/support_main.asp?id=208