Aneuploidy is often fatal, but there is "X-inactivation", where the effect of the additional gene dosage due to the presence of extra X chromosomes is greatly reduced.

These males also tend to exhibit more immature behavior for their chronological age; increased aggressive tendencies were also cited in this study.

[9] A 2020 study found that boys with 49,XXXXY have heightened rates of internalizing behavior and anxiety, beginning as early as preschool.

[4] An infant in Iran diagnosed with 49,XXXXY syndrome was born with patent ductus arteriosus, which was corrected with surgery, and other complications that were managed with replacement therapy.

[4] The administration of testosterone therapy has been shown to improve motor skills, speech, and nonverbal IQ in males with 49,XXXXY.