All the cells in our body have the same set of genes. The reason that we have arms, legs, heads, etc. is because transcription factors turn genes on and off in the right places at the right time. This report out of Colorado Springs shows what happens when genes get turned on in the wrong place. It appears that the poor child in this report was suffering from a teratoma: an inappropriately placed but otherwise normal-looking growth of a body structure in the form of a tumor. Fortunately, the child is alive and hopefully will recover fully.
The placement of a fully formed foot inside this child's brain shows how developmental programs are hard-wired in our genome. Once a cascade of transcription factors is triggered in a group of cells, it can autonomously create a full body structure such as a leg. In this case, something inappropriately triggered the cascade in the wrong place. Hopefully someday, we'll understand what causes things like this. Then, we might actually be able to re-grow structures for other unfortunate people who need an organ replaced.
I hope this kid is okay.
