Background: Swyer syndrome (46,XY pure gonadal dysgenesis) is a rare disorder of sex development presenting with primary amenorrhoea in phenotypic females. Familial occurrence is exceedingly uncommon.

Case Presentation: We report two affected siblings born to a non-consanguineous couple. A 19-year-old phenotypic female presented with primary amenorrhoea and Tanner stage 2 breast development. Hormonal evaluation revealed hypergonadotropic hypogonadism (FSH 18.7 mIU/ml, LH 11.7 mIU/ml). Karyotyping confirmed a 46,XY pattern. Pelvic imaging showed a hypoplastic uterus with absent ovaries, and laparoscopy revealed streak gonads, which were removed prophylactically. Her elder sibling was subsequently found to have identical clinical, hormonal, and cytogenetic findings and underwent similar management.

Conclusion: Swyer syndrome in siblings is a rare entity requiring high clinical suspicion in phenotypic females with primary amenorrhoea. Early diagnosis, karyotyping, prophylactic gonadectomy, and multidisciplinary care including psychological support are essential to prevent gonadal malignancy and improve outcomes.

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