Because of the intrinsic variability found in primary cells, the researchers had to rely on fluorescence lifetime imaging to probe the Zn2+ function in these cells. The observed ZIP7 mutations eliminated the natural Zn2+ gradient present in precursor B cells. The absence of this gradient is key for development of the immunodeficiency found in patients.
Consuelo Anzilotti et al:
An essential role for the Zn2+ transporter ZIP7 in B cell development
Nature Immunology volume 20, pages 350–361 (2019)