3q27.3 microdeletion syndrome is a rare chromosomal anomaly syndrome, resulting from the partial deletion of the long arm of chromosome 3, characterized by mild to severe intellectual disability, neuropsychiatric disorders of the psychotic and dysthymic spectrum, mild distinctive facial dysmorphism (incl. slender face, deep-set eyes, high nasal bridge with a hooked nose, small, low- set ears, short philtrum, small mouth with thin upper lip, prognathism) and a marfanoid habitus.

Height of the vermilion of the upper lip in the midline more than 2 SD below the mean. Alternatively, an apparently reduced height of the vermilion of the upper lip in the frontal view (subjective).