MBTPS2 and BRESEK syndrome: To test the ability of our patient‐identified variant to correct these deficiencies in vitro, we generated polyclonal Mbtps2‐deficient CHO cells (M19‐CHO) stably expressing vector alone (negative control), wild‐type MBTPS2 (positive control), Val256Leu‐MBTPS2 (patient‐identified variant), Arg429His‐MBTPS2 (BRESHECK syndrome control), and Gly500Asp‐MBTPS2 (IFAP control) via chemical transfection and G418 selection.