Among large deletions identified in patients, we found a female patient (MR_3067) with a 3.7 Mb deletion at 4q21 locus encompassing candidate genes PRKG2 and RASGEF1B. The patient showed gross developmental delay since birth, speech impairment, and generalized tonic-clonic seizure since 2 years old. The gene discussed is RASGEF1B; the disease is Global developmental delay.