What are Sex Chromosomal Aneuploidies? Sex chromosome aneuploidies (SCA) describe those conditions in which there is some variation among the normal euploidic sex chromosomes in male (XY) or female (XX) individuals. These variations are most often caused by non-disjunction of the 23rd sex chromosome pair during meiosis. Found in 1 in 400 live newborns, SCA are even more common than Down syndrome or fragile X syndrome. While SCA can include a variety of abnormalities of the sex chromosomes, by far the most commonly occurring SCA involve the deletion (45,X or partial X monosomy) or addition (47,XXY, 47,XYY, 47,XXX) of an X or Y chromosome. Of these conditions, only Turner syndrome, caused by the loss of all or part of an X chromosome, results in an easily identifiable physical phenotype. Subtle language, neuromotor, and learning difficulties have been identified in most forms of SCA, however. The neurodevelopmental effects of the 47XXY (Klinefelter syndrome) and 47XXX karyotypes are also investigated in light of these phenotypic features. Why do we study SCA? The genotypic alterations in SCA provide a clear biological causes for the study of genetic influences on phenotype, including neurodevelopment. Results from our current research are revealing neuroanatomical differences in the brains of these individuals which likely underlie their developmental impairments. The neuroanatomic regions of interest generated from this image processing pipeline include those volumes that are of interest in the various forms of SCA, given the phenotypic features of Turner syndrome, Klinefelter syndrome, and 47XXX. These include but are not limited to: total brain, parietal lobe, temporal lobe, occipital lobe, cerebellum, ventricular volume, hippocampus, amygdala, parahippocampal gyrus and superior temporal gyrus segmented white matter, gray matter, and cerebral spinal fluid (CSF) image volumes are also measured for these areas. Contact Information For more information about SCA imaging research at the Stanford University School of Medicine please contact Cindy Johnston, ckjohnston@stanford.edu Lucile Packard Children's Hospital is located in Palo Alto, adjacent to Stanford University Hospital, approximately 20 miles north of San Jose, CA and 40 miles south of San Francisco.
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