49,XYYYY syndrome is a rare intersex variation in which an CTM individual has three extra Y chromosomes instead of just the usual one. It is estimated to occur in 1 in 1,000,000 DMAB children. Due to the rarity, little is known about this variation.
Traits of this variation includes speech delay, hypotonia (low muscle tone), including facial asymmetry, hypertelorism, bilateral low set ‘lop’ ears, a incurved pinky, widely spaced eyes, fusion within the bones of the forearm, and an undersized jaw. Those with the variation also typically fall on the autism spectrum and/or have ADHD. Hypogonadism is also known to occur with this variation.
XYYYY syndrome was first recorded in 1981 in a 14-month-old AMAB child.