Among multiple annotated genes our patient is also haploinsufficient for the following genes: RASGEF1B being a strong candidate for the neurodevelopmental features and PRKG2 for severe growth delay.<h4>Conclusion</h4>The first Hungarian case of 4q21 deletion adds to the phenotypic spectrum of this novel microdeletion syndrome and underlines the importance of array CGH to uncover the heterogeneous causes of intellectual disability. The gene discussed is RASGEF1B; the disease is Intellectual disability.