Neurodevelopmental Profile of a 4.5-Year-Old Girl with Tetrasomy X

<b>Background</b>: Tetrasomy X (48, XXXX) is an extremely rare sex chromosome aneuploidy characterized by highly variable phenotypic manifestations. It includes various medical issues, a wide range of developmental delays, and neurocognitive deficits. <b>Methods</b>: The present case report provides a comprehensive neurodevelopmental profile of a 4.5-year-old girl with Tetrasomy X, with the aim of contributing to phenotype delineation, exploring genotype-phenotype associations, and emphasizing the importance of early, targeted intervention. A multidisciplinary assessment was conducted, encompassing cognitive, speech-language, motor, sensory, adaptive, and socioemotional functioning, using a battery of standardized and culturally adapted instruments. <b>Results</b>: Results revealed borderline intellectual functioning and mild global developmental delay, with marked intra-individual variability across domains. Motor development was significantly delayed and speech and language assessment demonstrated a pronounced receptive-expressive discrepancy. Sensory processing evaluation revealed a pattern of global sensory under-responsiveness, representing a novel and underreported feature in Tetrasomy X. Adaptive functioning was uneven, with relative strengths in daily living skills and weaknesses in motor abilities. <b>Conclusions</b>: This detailed early developmental characterization highlights the heterogeneity of Tetrasomy X and challenges some of the previous assumptions. The findings underscore the necessity of individualized, multidisciplinary assessment and early intervention to optimize developmental outcomes and quality of life in affected individuals.