Tetrasomy 18p is a very rare structural chromosomal anomaly affecting multiple body systems and characterized clinically by craniofacial abnormalities, delayed development, cognitive impairment, changes in muscle tone, distinctive facial features, and rarely renal malformations.

Distance between nasal base and midline upper lip vermilion border more than 2 SD above the mean. Alternatively, an apparently increased distance between nasal base and midline upper lip vermilion border.