ABSTRACT
A patient with global developmental delay and facial abnormality treated in Hunan Maternal and Child Health Care Hospital in September 2018 was diagnosed as a typical Say-Barber-Biesecker/Young-Simpson syndrome (SBBYSS)accompanied with comprehensive clinical manifestations and genetic testing was carried out.The patient carries a heterozygous synonymous mutation of KAT6B gene (NM_012330.3)c.3147G>A (p.P1049P), thus leading to the formation of a new cleavage site (receptor) and forming a new truncated protein.In Chinese, this is the second typical SBBYSS that has been identified and the first prenatal genetic diagnosis has been performed.This study has broadened the mutation spectrum of SBBYSS caused by the mutation of KAT6B gene in Chinese population.