Cornelia de Lange syndrome (CdLS) is a developmental disorder that affects between one in 10,000 to 30,000 neonates. Affected infants are characterized by slow post and prenatal growth, distinctive facial features, severe to profound mental retardation, and upper limb reduction defects, ranging from minor phalangeal abnormalities to oligodactyly. Abnormal facial features typical of CdLS include microcephaly, arched confluent eyebrows, long eyelashes, low-set ears, low hairlines, small, upturned nose, cleft palate, small widely spaced teeth, and a small lower jaw. Other features seen in this condition are hirsutism, hearing loss, cryptorchidism, myopia, cardiac septal defects, as well as autistic features. Average IQ levels are around 53.

At least three different genes have been implicated in the development of CdLS. About 30-50% of cases of the condition have been shown to be due to mutations in the NIPBL gene. This gene, codes for a protein known as delangin, which is assumed to play a role in embryonal development. The specific role this protein is not clearly known. However, there is evidence to show that the delangin protein may be playing a structural role in chromatin formation and sister chromatid cohesion.