Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Beuschlein et al. (2013) identified somatic mutations in the ATP1A1 gene encoding Na+/K+ ATPase α subunit and the ATP2B3 gene encoding Ca2+ ATPase in APA, which are genes involved in regulating sodium, potassium, and calcium ion homeostasis.
Category: