XXYY or 48,XXYY syndrome or 48,XXYY is a rare intersex trait occurring in approximately 1 in 18,000 to 1 in 40,000 people who are AMAB.[2] It is a chromosomal condition that causes them to have an extra X and an extra Y chromosome (XXYY). It may be considered a variant of Klinefelter syndrome. Those with the the condition typically have small testes that do not produce enough testosterone, which can lead to reduced facial and body hair, poor muscle development, breast growth, and infertility. Other common symptoms can include increased height, dental problems, problems with blood vessels in the legs, difficulty with language development, delayed development of motor skills, tremors that typically starts in adolescence and increases with age, and an increased likelihood of several other physical and neurological conditions.[3]