The heterozygous mutation of the KAT6B gene can cause SBBYSS (Say-Barber-Biesecker-Young-Simpson syndrome), a rare form of mental retardation and related syndromes, which is mainly manifested as severe mental retardation, special facial features, bone and genital abnormalities [22]. The gene discussed is KAT6B; the disease is blepharophimosis - intellectual disability syndrome, SBBYS type.