Which of the following disorders is NOT associated with a microdeletion?

Rubinstein-Taybi syndrome is primarily caused by mutations in the CREBBP or EP300 genes rather than a microdeletion. This disorder is characterized by distinct physical features, broad thumbs and toes, and various developmental issues. In contrast, the other disorders listed are known to be associated with specific microdeletions.

Prader-Willi syndrome is linked to a deletion of paternal genes on chromosome 15. DiGeorge syndrome, also connected to chromosome 22, is due to a deletion that affects the development of several body systems. Similarly, Langer-Giedion syndrome is associated with deletions in chromosome 8. Therefore, Rubinstein-Taybi stands apart because its etiology is based on point mutations rather than a microdeletion, reflecting a different genetic mechanism. This distinction clarifies why it is the correct answer in the context of disorders associated with microdeletions.