We give examples of where the Heun function exists as solutions ofwave equations encountered in general relativity. While the Diracequation written in the background of Nutku helicoid metric yieldsMathieu functions as its solutions in four spacetime dimensions,the trivial generalization to five dimensions results in thedouble confluent Heun function. We reduce this solution to theMathieu function with some transformations. We must applyAtiyah-Patodi-Singer spectral boundary conditions to this systemsince the metric has a singularity at the origin.