Clinical, Biochemical, and Cytogenetic Heterogeneity in Mosaic 46,XX/47,XXY Sex Chromosome Aneuploidy

Mosaic sex chromosome aneuploidy 47,XXY/46,XX is an exceptionally rare variant within the spectrum of Klinefelter syndrome. Available data remain limited, especially regarding adult phenotype and long-term characteristics, and no robust comparative data with non-mosaic 47,XXY Klinefelter syndrome are currently available. This retrospective monocentric comparative study is designed to describe the clinical, biochemical, cytogenetic, gonadal, anthropometric, and socio-professional characteristics of adults with 47,XXY/46,XX mosaicism. In addition, the study is intended to compare these characteristics with those of a homogeneous cohort of individuals with non-mosaic 47,XXY Klinefelter syndrome and with previously published case reports, in order to improve phenotypic characterization of this rare chromosomal condition.