We report on a six-year-old boy with typical Rubinstein-Taybi syndrome (RSTS) 
phenotype. Clinical findings included mental and motor retardation, patent 
ductus arteriosus (PDA), undescended testes, hirsutism, broad thumbs with radial 
angulation and broad toes, and inguinal hernia. His karyotype was normal (46, 
XY) and fluorescence in situ hybridization (FISH) showed no deletion of the 
CREBBP [cAMP response element-binding (CREB) binding protein] gene on chromosome 
16p13.3. CREBBP gene sequencing also revealed normal results. We wish to present 
this case because this patient had typical RSTS phenotype, but normal FISH and 
CREBBP gene sequencing results. It could be possible that genetic heterogeneity 
is related with novel mutations in other genes. With the publication of such 
cases, their significance will be brought to the attention of researchers in 
this field.