Background/Purpose: 45,X/46,XY mosaicism is a rare sex chromosome abnormality. Here, we present our experience in the management of 45,X/46,XY Taiwanese children. Patients and Methods: We enrolled 19 patients from January 1981 to September 2016. The diagnosis of 45,X/46,XY mosaicism was made by karyotyping peripheral blood lymphocytes. All medical records were thoroughly reviewed. Results: Of the 19 patients, 16 were reared as females and 3 as males. The age at diagnosis ranged from 1 month to 15 years and 9 months. Atypical genitalia, short stature, and Turner stigmata were common manifestations. No patient exhibited a cardiac malformation but 29% had renal malformations and 12.5% had autoimmune thyroid disease who developed thyroid dysfunction later. Nine girls with short stature received growth hormone therapy and their height standard deviation score rose from −3.4 ± 1.1 to −1.4 ± 0.9 in adulthood (P < 0.01). The gonadal phenotypes included bilateral streak gonads in nine patients, a streak gonad with contralateral gonadal agenesis in one, mixed gonadal dysgenesis in five, bilateral dysgenetic testes in two, and bilateral gonadoblastomas in one. Conclusion: The 45,X/46,XY phenotype varies widely and a high index of suspicion is important to ensure early diagnosis. Cardiac and renal malformations should be screened ultrasonically at diagnosis and thyroid status should be monitored annually. Growth hormone effectively improves adult height in short girls. Prophylactic gonadectomy is indicated for those with intra-abdominal streaks or dysgenetic gonads to prevent the development of a malignancy.
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