GCK and type 2 diabetes mellitus: Nevertheless, we clearly saw evidence of incomplete penetrance for all gene-conditions with the only exception of GCK-MODY; in both datasets 100% (17/17) of carriers of clinically significant GCK variants developed diabetes or prediabetes (penetrance estimates of 100%, 95% CI: 59.0–100% in AMP-T2D-GENES and 69.2–100% in UKB) (Fig. 3B, Supplementary Data 3, 5).