FRI452 A Rare Case of Klinefelter Syndrome, 48XXYY

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Abstract Disclosure: P. Kachhadia: None. S. Khan: None. S. Aldasouqi: None. A. Abu Limon: None. Introduction: Klinefelter Syndrome (KS), 47XXY, is the most commonly seen chromosomal abnormality causing infertility, or primary hypogonadism. Other chromosomal variants are rare. We present a very rare case of nondisjunction of the sex chromosome resulting in a 48XXYY KS variant. Case Presentation: The patient is a 45-year-old male was referred to our clinic for evaluation of early onset osteoporosis. The patient was accompanied by his sister, given his cognitive delay. On initial physical exam, there was a concern about acromegaly with signs of frontal bossing, increased hand size, increased ring size and increased shoe size. More recent pictures of the patient showed significant changes in his facial appearance from few years prior. Other symptoms included night sweats. Physical exam revealed decreased testicular volume (less than 3mL bilaterally). Pituitary labs showed elevated prolactin, elevated LH, FSH and low free and total testosterone. GH, IGF-1 levels were within normal range. Chromosomal analysis showed an unexpected pattern of 48XXYY. In addition, MRI of the pituitary was done which showed increased infundibular stalk and increase in size of the pituitary gland which was thought to be secondary to pituitary microadenoma. DEXA scan confirmed osteoporosis. Patient was treated with testosterone injections and alendronate. The rationale for alendronate therapy was considered as a bridge to prevent fractures while the bone density would expectedly improve with androgen therapy, over time. Discussion: Although KS is commonly seen at a frequency of 1:500-1:1000 males, less common and variable phenotypical presentations can occur and can lead to a delayed diagnosis. The reason for the delay of diagnosis in these rare KS variants is the cognitive impairment which leads to delayed evaluation of fertility or hypogonadism, as contrasted to patients with the common variant, KS 47XXY. Additionally, unlike the classic KS variant, these rare variants are often associated with learning disabilities and gross bony features. Conclusion: Clinicians should be familiar with different clinical presentations of the less common KS genetic variants, in contrast to classical KS variants. Patients with classical KS typically present early in view of recognizable complaints of infertility, while patients with the less common KS variants may not present early on due to cognitive delay. Thus, familiarity with the additional manifestations of the less common KS variants (e.g., gross bony features) can help clinicians to suspect the possibility of these variants, prompting chromosomal analysis for further evaluation in such patients. Presentation Date: Friday, June 16, 2023