These studies have found that ~ 70–80% of causal variants are in either GCK or HNF1A. Small-scale studies of South Asian MODY patients have indicated that substantially fewer MODY cases can be explained by variants in HNF1A [11, 12], HNF4A [13], GCK [14] and HNF1B [15]. The gene discussed is HNF1B; the disease is MODY.