Mosaic trisomy 14 is a rare chromosomal disorder in which there are 3 copies (trisomy) of chromosome 14 in some cells of the body, while other cells have the usual two copies. The extent and severity of features in affected individuals can vary. Signs and symptoms that have been most commonly reported include intrauterine growth restriction; failure to to thrive; developmental delay; intellectual disability; distinctive facial characteristics; structural malformations of the heart; and other physical abnormalities. This condition is most often caused by an error in cell division in the egg or sperm cell before conception, or in fetal cells after fertilization.