As Pillsy remarked, all symbols are upper-cased by default when they are read by the Lisp compiler. There is a way of turning that off, though. See the CLHS, 23.1.2 (Effect of Readtable Case on the Lisp Reader), and the description of the accessor readtable-case
for details. As an example, you can enable the “invert” mode (which is arguably the only practical setting that is also case-sensitive) by putting the following into your Lisp source file:
#.(setf (readtable-case *readtable*) :invert)
Unfortunately, ParenScript does not seem to make much use of a custom readtable-case setting, even though it could (and, in my opinion, should) do so.