Herein, we are going to report a 14-year-old developmental delay boy with cognitive impairment, significant facial dysmorphisms, undescended testes and bilateral hypoplasis of patellae as a new case of SBBYSS in Iranian population, which is caused by de novo mutation in KAT6B gene. This evidence concerns the gene KAT6B and blepharophimosis - intellectual disability syndrome, SBBYS type.