[BioC] DESeq2 : when the variable of interest is not a factor

[Marie Sémon]

Dear all,

I wish to find genes whose expression profile correlates with a variable 
of interest, which is quantitative (say, the weight of the individuals). 
Is it possible/a good practice to use DESeq2 for this?

One one hand the vignette clearly describes factors (qualitative) 
variables, but, on the other hand there is this sentence, p8:
"If the variable of interest is not a factor, the log2 fold change can 
be interpreted as the amount of doubling observed on average for every 
unit of change."

Many thanks for you help

With kind regards,

Marie