A 26-yr-old phenotypic male with moderately severe mental retardation and clinical evidence of Klinefelter's syndrome has been found to have an XXXYY sex-chromosome complex. This chromosomal constitution has not previously been reported in patients with seminiferous tubule dysgenesis. The positive nuclear chromatin on buccal smear and the appearance of occasional double chromatin masses are compatible with the triple X portion of the sex-chromosome constitution. The severity of the mental defect and the testicular changes may be proportional to the number of supernumerary X chromosomes, as suggested by others, but a review of literature shows that statistical proof for this theory is lacking. The clinical significance of an extra Y chromosome remains unknown, but the acromegalic features in this and another patient reported merit contemplation and further study.
Bray P, Josephine A. An XXXYY Sex-Chromosome Anomaly: Report of a Mentally Deficient Male. JAMA. 1963;184(3):179–182. doi:10.1001/jama.1963.03700160055007
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