Background: Supernumerary sex chromosome aneuploidies (sSCA) are characterized by the presence of one or\nmore additional sex chromosomes in an individual�s karyotype; they affect around 1 in 400 individuals. Although\nthere is high variability, each sSCA subtype has a characteristic set of cognitive and physical phenotypes. Here, we\ninvestigated the differences in the morphometry of the human corpus callosum (CC) between sex-matched controls\n46,XY (N =99), 46,XX (N =93), and six unique sSCA karyotypes: 47,XYY (N =29), 47,XXY (N =58), 48,XXYY (N =20),\n47,XXX (N =30), 48,XXXY (N =5), and 49,XXXXY (N =6).\nMethods: We investigated CC morphometry using local and global area, local curvature of the CC boundary, and\nbetween-landmark distance analysis (BLDA). We hypothesized that CC morphometry would vary differentially along\na proposed spectrum of Y:X chromosome ratio with supernumerary Y karyotypes having the largest CC areas and\nsupernumerary X karyotypes having significantly smaller CC areas. To investigate this, we defined an sSCA spectrum\nbased on a descending Y:X karyotype ratio: 47,XYY, 46,XY, 48,XXYY, 47,XXY, 48,XXXY, 49,XXXXY, 46,XX, 47,XXX. We\nsimilarly explored the effects of both X and Y chromosome numbers within sex. Results of shape-based metrics\nwere analyzed using permutation tests consisting of 5,000 iterations.\nResults: Several subregional areas, local curvature, and BLDs differed between groups.\nModerate associations were found between area and curvature in relation to the spectrum and X and Y chromosome\ncounts. BLD was strongly associated with X chromosome count in both male and female groups.\nConclusions: Our results suggest that X- and Y-linked genes have differential effects on CC morphometry. To our\nknowledge, this is the first study to compare CC morphometry across these extremely rare groups.
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