Klinefelter syndrome, a congenital chromosomal abnormality with one or more extra X chromosomes, occurs in out of 400 live male births. The majority of Klinefelter men present with a 47, XXY karyotype. The "poly-X variant", with the 49,XXXXY karyotype is uncommon. This syndrome, where subjects have two or more X chromosomes presents with primary hypogonadism, and, particularly if associated with the 49,XXXXY karyotype, significantly impacts life skills across a variety of dimensions, including areas of communication, community use, functional academics, home/school living, health and safety, leisure, self-care, self direction, and work. Adaptive behavior abnormalities in 46,XXY men are well known and described. In the poly-X variant of the 49,XXXXY karyotype, adaptive behavior abnormalities are expected to be much more significant, making these patients eligible for services and Social Security benefits.

In 49,XXXXY men no study to date has examined these areas of inquiry in a large patient population, using a psychometrically sound instrument in a large patient population. Current publications are limited to individual case reports or small case summaries. It is important to study the adaptive behavior in its highly abnormal presentation in 49,XXXXY men in order to learn more about the effect of additional X chromosomes on adaptive skills, which determine how an individual responds to daily demands and in order to develop treatment and training goals.