Cri-du-chat syndrome is a rare cytogenetic disorder first described by Jerome Lejuene in 1963. The syndrome results from a missing piece of chromosome 5. The name of the syndrome comes from the characteristic cat like cry of infants with this condition (cri du chat being a French term for 'call of the cat'), which itself originates from laryngeal problems. Other characteristics of the disorder include mental retardation, developmental delay, low birth weight and delayed growth, microcephaly, infantile hypotonia, partial digital webbing, and a single transverse palmar crease. Affected patients also typically show several dysmorphic features, including hypertelorism and downwardly slanting eyes, low-set ears, micrognathia, rounded face, and preauricular tags. Some affected neonates have congenital cardiac defects.

One in approximately 20,000 to 50,000 neonates is estimated to be born with this condition. Interestingly, cri du chat syndrome is slightly more common in females. Among individuals with severe mental retardation, this syndrome is accountable for up to 1% of the cases. As in the case of most other cytogenetic abnormalities, no specific treatment is available for this syndrome. Prognosis depends of the severity of the condition. Half of children with cri du chat syndrome learn sufficient verbal skills to communicate. Prenatal diagnosis of the condition is possible and widely available.

Cri-du-chat syndrome is due to a partial deletion in the small arm of chromosome 5. In 90% of the cases, this is a de novo deletion, with no family history of such a condition. Interestingly, within this de novo group, in about 80% of the cases, the deletion is in the paternal chromosome. In the remaining 10% of the cases, the condition is due to a parental balanced translocation. Such cases have a more severe form of the condition when compared to the de novo cases.

Within the deleted region, a small sub-region, called the Cri Du Chat Critical Region accounts for most of the clinical features associated with the syndrome. The phenotype of the cat like cry corresponds to a different locus in the region. Two genes within the deleted region, SEMA5A and CTNND2, have been shown to play a role in cerebral development, which might explain the intellectual impairment and neurological dysfunction characteristic of the syndrome.