Cri-du-chat (French for "cat's cry") is a congenital syndrome in humans caused by the loss of genetic material on the short arm of the 5th chromosome. The syndrome, which was first described by a researcher named Lejeune in 1963, gets its name because infants and young children with the disorder make a high-pitched, cat-like crying noise.

Children with the syndrome tend to have round faces, low-set ears, small jaws and abnormally small heads (microcephaly). They also exhibit a lack of normal muscle tone and they usually have moderate-to-severe mental and psychomotor retardation. They may have other physical problems such as scoliosis and deformities of their internal organs. About 1 in 50,000 babies are born with the syndrome; it is one of the most common syndromes caused by genetic deletions.

Many people with cri-du-chat have periods of aggressive, destructive behavior and self-mutilation, and they typically have trouble with speech. However, with early childhood educational intervention and physical therapy, children with milder forms of the syndrome can attend school and experience a full life.

Cri du Chat Syndrome is a genetic disorder resulting from the deletion of genetic material on the short arm of the fifth chromosome. It is also known as 5P Minus Syndrome, Lejeune's Syndrome, and Cat-cry Syndrome.

The syndrome was first discovered in 1963 by Jerome Lejeune, the man who also identified the genetic cause of Downs Syndrome. One of the most prominent characteristics of the syndrome is a cat-like monotone mewing made by newborns with the disorder, hence Cri du Chat ("Cry of the Cat" in French). The noise is still one of the most important symptoms that lead to diagnosis today and is most likely due to structural laryngeal abnormality and hypotonia. Infants with the disorder tend to have a low birth weight, have marked hypotonia, and have feeding difficulties. Physical abnormalities that come with Cri du Chat include microcephaly, micrognathia, rounded face, macrostomia, hypertelorism with downward sloping palpebral fissures, low set ears, broad nasal ridge and short neck. With age, people with the disorder tend to have a long face, suffer from scoliosis and macrostomia, and are more prone to respiratory infections and dental problems. Although originally it was thought to affect 1 in 50,000 live births it is now thought to occur in 1 or 37,000 live births. A CVS or amniocentesis can detect the disorder during pregnancy. 85% of cases are sporadic, although the remaining cases occur in families with a history of Cri du Chat.

About 80% of occurrences of Cri du Chat are caused by a spontaneous deletion of the genetic material in the child, 10-13% are due to errors in the fifth chromosome in one or both of the parents, and the remaining 7-10% are caused by rare genetic abnormalities. It is thought to be more common in females. The gene which causes the distinctive cry is thought to be located on band 15.3, which would explain why although some babies who have Cri du Chat do not have the cry while some children who do don't suffer from Cri du Chat.

Many people with Cri du Chat Syndrome survive to adulthood. Severe learning disabilities are the norm in addition to a low IQ. People with Cri du Chat also tend to be hyperactive and self-injurious, mostly by head banging and biting, reaching its height in late childhood and continuing through adulthood.

The Short Arm 5P of Chromosome 5:
 |    - 5p 15.33
 |    - 5p 15.32
 |    - 5p 15.31-3
 |    - 5p 15.31-2
 |    - 5p 15.31-1 (Region thoguht to be responsible for the cry)
 |    - 5p 15.2 (Region for main features of the syndrome, except the cry)
 |    - 5p 15.1-3
 |    - 5p 15.1-2
 |    - 5p 15.1-1
 |    - band 5p 14
 |    - 5p 13.3
 |    - 5p 13.2
 |    - 5p 13.1
 |    - 5p 12
 |    - 5p 11
 O    - centromere
 |    - long arm 5Q

(not to scale)

Sources:
http://www.cafamily.org.uk/Direct/c81.html
http://www.criduchat.asn.au/criduchat/what.htm#Cri%20du%20Chat%20Syndrome