  We give examples of where the Heun function exists as solutions of wave
equations encountered in general relativity. While the Dirac equation written
in the background of Nutku helicoid metric yields Mathieu functions as its
solutions in four spacetime dimensions, the trivial generalization to five
dimensions results in the double confluent Heun function. We reduce this
solution to the Mathieu function with some transformations. We must apply
Atiyah-Patodi-Singer spectral boundary conditions to this system since the
metric has a singularity at the origin.
