C syndrome, also known as Opitz trigonocephaly syndrome, is a rare disorder transmitted as a result of "gonadal mosaicism". Mosaicism refers to a condition in which a person has cells that differ from each other in genetic makeup. The difference is usually a variation in the number of chromosomes. Normally, all body cells would have 46 chromosomes, but in mosaicism, some cells may have 45 or 47. Mosaicism occurs as a result of an error in cell division very early in fetal development.
Affected individuals are born with a malformation in which the head is a triangular shape due to premature union of the skull bones (trigonocephaly), a narrow pointed forehead, a flat broad nasal bridge with a short nose, vertical folds over the inner corners of the eyes, an abnormal palate that is deeply furrowed, abnormalities of the ear, crossed eyes (strabismus), joints that are bent or in a fixed position, and loose skin. Developmental and learning disabilities are common.