XXYY Syndrome

The XXYY flag.

XXYY or 48,XXYY syndrome or 48,XXYY is a rare intersex trait occurring in approximately 1 in 18,000 or 1 out of 40,000 people who are assigned male at birth, and causes them to have an extra X and an extra Y chromosome.

Resources

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3056496/
2. https://rarediseases.info.nih.gov/diseases/5677/48xxyy-syndrome
3. https://www.deviantart.com/pride-flags/art/XXYY-Syndrome-657913826