Karyotype — Klinefelter Variant 48,XXXY

A 14-year-old boy presents to the pediatric endocrinology clinic with short stature, gynecomastia, and a history of significant speech delay and intellectual disability (IQ 45). Physical examination reveals characteristic facial dysmorphism with hypertelorism and epicanthal folds, small firm testes, and notably limited forearm pronation and supination bilaterally. Karyotype analysis shows 48,XXXY. The structure marked **A** in the diagram represents the three X chromosomes present in this patient's karyotype. Which of the following best explains the SEVERITY of the intellectual disability and dysmorphic features observed in this patient compared to a boy with classic 47,XXY Klinefelter syndrome?