What is the characteristic defect noted in Rubinstein-Taybi syndrome?

Rubinstein-Taybi syndrome is a genetic condition characterized by several distinct features. Among these, growth and mental retardation are commonly observed, meaning individuals with this syndrome often experience delays in their physical and intellectual development.

Facial dysmorphism is also a hallmark of this condition, characterized by specific facial features that can include a rounded face, beaked nose, and wide-set eyes, among others. These distinctive facial traits help in identifying the syndrome.

Another significant characteristic of Rubinstein-Taybi syndrome is the presence of broad thumbs and toes. This feature can lead to a unique appearance of the hands and feet, further aiding in the diagnosis.

Given that all these aspects—growth and mental retardation, facial dysmorphism, and broad thumbs and toes—are integral components of Rubinstein-Taybi syndrome, it is clear that the most comprehensive answer encompasses all three features. Therefore, the correct choice reflects the combined presence of these characteristics.