I want to know the answer to the following question:
What is the Drosophila gene the cause of?
All the background I'm provided with is that "A defect in the human homologue of the Drosophila "period" gene was identified as a cause of the sleep disorder FASPS (Familial advanced sleep phase syndrome), underscoring the conserved nature of the molecular circadian clock through evolution.". Is that enough to answer the question?