Our study observed two homozygous ONECUT1 variants in Arab patients of diabetes—the deleterious missense rs202151356_p.H33Q was observed in 1 individual of MODY, 1 individual of T1D and two individuals of T2D; and the synonymous rs61735385_p.P94P was observed in two T2D individuals. This evidence concerns the gene ONECUT1 and type 1 diabetes mellitus.