ABSTRACT
Tetrasomy 18p is a genetic syndrome caused by an isochromosome consisting of two copies of the short arm of chromosome 18. Clinically, pediatric cases of tetrasomy 18p manifest with global developmental delay, similar to most cases of chromosomal abnormality. In addition, it causes various symptoms including abnormal muscle tone. We report a case of an infant with global developmental delay and remarkable spasticity, the typical phenotype of bilateral spastic cerebral palsy. However, she had a subtle anomaly in her face, and brain magnetic resonance imaging (MRI) findings were inconsistent with her strong upper motor neuron signs. Upon genetic testing, she was determined to have an 18p isochromosome, confirming de novo non-mosaic tetrasomy 18p. Cerebral palsy is a neurological disorder that includes developmental delay caused by a non-progressive lesion in the developing brain. During diagnostic workup in patients with cerebral palsy, genetic testing should be considered when there are minor physical anomalies or equivocal MRI findings.