Significant trauma can induce stuttering, even in the absence of genetic predisposition or neurophysiologic factors. Check out Johnson's aptly-named [Monster Study](http://en.wikipedia.org/wiki/Monster_Study). Also, as far as we know, the OP could have some of those neurophysiologic predispositions (unless s/he's had an fMRI that distinctly indicates a "non-stuttering brain"). If you follow the [Bucket Analogy](http://www.mnsu.edu/comdis/isad11/papers/therapy11/coleman11/coleman11.html), this kind of childhood experience on its own could qualify to "fill" the bucket. Or if not, only very minor environmental/physical/biological factors would be required to tip the scales.