Introduction: 45,X/46,XY mosaicism is a rare disorder of sex development characterized by marked phenotypic variability, ranging from typical male or female genitalia to significant genital ambiguity. Data describing long-term clinical outcomes in affected patients remain limited. This study aimed to characterize the phenotypic spectrum and longitudinal outcomes of patients with 45,X/46,XY mosaicism, focusing on growth, associated comorbidities, and gonadal pathology. Methodology: We conducted a retrospective longitudinal study at a tertiary paediatric endocrine referral centre between January 2006 and January 2025. Patients with cytogenetically confirmed 45,X/46,XY mosaicism or related variants were included. Clinical presentation, karyotype, anthropometry, hormonal profiles, imaging findings, and gonadal histology were reviewed. External genital phenotype was quantified using the External Masculinization Score (EMS). Height was expressed as standard deviation scores (SDS) relative to population norms and compared with genetic potential. Results: Fourteen patients (10 males, 4 females) with 45,X/46,XY mosaicism were identified. Ambiguous genitalia was the predominant presenting feature, observed in 11 of 12 patients with available phenotype data. Growth impairment was common; median height SDS was −2.62 (range −3.26 to −2.00) in females and −0.46 (range 0.13 to −1.70) in males, both below expected genetic potential. Associated congenital anomalies were present in 25% of patients, including cardiac and renal abnormalities. Male patients demonstrated variable degrees of undervirilization with a median EMS of 4.5 (3.75–7.25). Müllerian duct remnants were identified in 66% of patients on imaging. Testicular microlithiasis was observed in two males. During follow-up, two patients underwent gender reassignment. Histological analysis of 14 gonads obtained via gonadectomy or biopsy revealed abnormal gonadal architecture in all cases. All intra-abdominal gonads demonstrated streak gonads or dysgenetic testicular tissue. Conclusion 45,X/46,XY mosaicism demonstrates a broad phenotypic spectrum with frequent genital ambiguity, growth impairment, and abnormal gonadal development. The high prevalence of gonadal dysgenesis underscores the importance of careful surveillance and individualized multidisciplinary management guided by clinical, endocrine, and histopathological findings.
Child ; Longitudinal Studies ; Mosaicism