Clinical and Genetic Characteristics of De Novo Tetrasomy 18p in Early Infancy: A Case Report

Tetrasomy 18p is a rare chromosomal disorder caused by the presence of an isochromosome consisting of two copies of the short arm of chromosome 18, resulting in four copies of 18p. It is typically sporadic and presents with a wide spectrum of clinical manifestations, including developmental delay, hypotonia, dysmorphic features, and multi-system involvement. Detailed phenotypic descriptions of this rare disorder are limited in the literature We report a 9.5-month-old male infant with dysmorphic features, feeding difficulties, recurrent respiratory infections, hypotonia, and global developmental delay. Neuroimaging showed agenesis of the corpus callosum, and echocardiography revealed a tiny muscular ventricular septal defect. Chromosomal microarray confirmed a de novo pathogenic duplication of chromosome 18p. The patient is undergoing multidisciplinary supportive care, which includes developmental therapies and regular cardiac and neurological check-ups. This case highlights the variable and multisystemic presentation of tetrasomy 18p and underscores the importance of comprehensive genetic evaluation in infants with dysmorphic features and developmental delay. Early diagnosis facilitates timely multidisciplinary intervention and improves long-term developmental outcomes.