International 15q Day, observed on the 15th of November, is dedicated  to raising awareness of several neurodevelopmental disorders caused by alterations in the q11 to q13 region of chromosome 15, commonly referred to as 15q. These disorders include Prader-Willi syndrome, Angelman syndrome, and Dup15q syndrome, all of which stem from specific changes within this critical region.

•  Prader-Willi syndrome occurs when the q11 to q13 region of the paternal (father's) chromosome is missing.
• Angelman syndrome arises when this region is absent from the maternal (mother's) chromosome.
• Dup15q syndrome is caused by a duplication of the q11 to q13 region from either parent, resulting in extra genetic material.

In addition to these, there are rarer conditions linked to abnormalities on chromosome 15, such as Schaaf-Yang syndrome, 15q13.3 microdeletion, and 15q11.2 microdeletion. These also involve anomalies in different parts of the chromosome, contributing to a variety of developmental challenges.

International 15q Day serves to promote understanding of these complex conditions and offers support to the individuals and families affected by them.