45,X/46,XY mosaicism: Clinical manifestations and long term follow‐up

45,X/46,XY chromosomal mosaicism presents a range of clinical manifestations, including phenotypes from Turner syndrome through genital abnormalities to apparently unaffected phenotypic males; however, the full clinical spectrum has not yet been fully delineated since prior studies on the clinical phenotype and associated risk of gonadal tumors included small cohorts and limited follow-up. To better describe the clinical manifestations and long-term outcome of patients with 45,X/46,XY mosaicism. We conducted a retrospective chart review of patients with 45,X/46,XY from three health centers (Hospital for Sick Children and Mount Sinai Hospital in Canada, and University of Pittsburgh Medical Center in United States). Of 100 patients with 45,X/46,XY karyotype, 47 were raised as females and 53 as males. Females were significantly shorter than males (p = 0.04) and height Z-score was significantly decreased with age for both genders (p = 0.02). Growth hormone (GH) treatment did not result in a significant height increase compared to the untreated group (p = 0.5). All females required puberty induction in contrast to majority of males. Five females were diagnosed with gonadal tumors, while no males were affected. Around 58% of patients exhibited at least one Turner syndrome stigmata. This study expands the clinical spectrum, long-term outcomes, and associated tumor risk in a large cohort of patients with 45,X/46,XY mosaicism. Additionally, it highlights our experience with GH therapy and prophylactic gonadectomy.