EP1336 - ECE_1771 - Unmasking XXYY syndrome: a case report highlighting endocrine and neurological manifestations

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Abstract Background XXYY syndrome is a rare sex chromosome aneuploidy, most commonly resulting from meiotic nondisjunction during spermatogenesis and, less frequently, from post-zygotic mitotic errors occurring in early embryogenesis.1 The condition is classically associated with increased height, gonadal dysfunction, and a wide spectrum of neurodevelopmental and behavioral abnormalities.2 Case Presentation: We report the case of a male patient, the first child of a non-consanguineous couple, born at term with documented perinatal distress. Initial developmental assessment revealed delayed gross motor milestone acquisition; however, significant improvement in motor function was observed following early intervention and structured rehabilitation. At 8 years of age, the patient underwent a comprehensive neurological evaluation after three epileptic seizure episodes. Brain magnetic resonance imaging identified a pineal region tumor, radiologically consistent with a pinealocytoma, measuring 11 × 11 × 12.7 mm. Serum α-fetoprotein and β-human chorionic gonadotropin were negative. Serial imaging demonstrated stability in lesion size over time. Therapy with valproate was initiated and maintained for two years, after which treatment was discontinued at the family's request, with no subsequent seizure recurrence. The patient was also diagnosed with mild intellectual disability, mixed-type attention-deficit/hyperactivity disorder and socio-pragmatic communication disorder. At the age of 16, he was referred for endocrine evaluation due to incomplete pubertal development, six years after pubertal onset. Presenting complaints included progressive weight gain, psychomotor agitation, and aggressive behavior. Physical examination revealed extreme tall stature (+3.91 SD), obesity, eunuchoid body proportions, and Tanner stage III pubertal development. Laboratory investigations demonstrated hypergonadotropic hypogonadism, primary hypothyroidism and dyslipidemia. Based on the clinical and hormonal findings, Klinefelter syndrome was initially suspected, prompting cytogenetic analysis, which ultimately revealed a diagnosis of 48,XXYY syndrome. Hormone replacement therapy with levothyroxine and transdermal testosterone was initiated, leading to a favorable clinical evolution. Conclusions This case illustrates the marked phenotypic diversity of XXYY syndrome. The coexistence of hypergonadotropic hypogonadism with tall stature, primary hypothyroidism, obesity, epilepsy, cognitive impairment, and a pineal region tumor highlights the diagnostic complexity of this condition. Early recognition and cytogenetic confirmation are essential to enable tailored hormonal therapy and coordinated multidisciplinary follow-up.

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