Newborns with cri du chat (cat's cry) syndrome have a characteristic mewing cry believed caused by abnormal development of the larynx (the organ containing the vocal chords). The syndrome arises from what is known as a deletion--the absence of genetic material from a missing portion of a chromosome. In cri du chat syndrome, the deletion is in chromosome 5. The disorder is also called 5p- (5 p minus) syndrome, in reference to the area where the deletion occurs. Children with this syndrome have physical abnormalities, language and motor skill difficulties, and varying degrees of mental retardation.

Although all individuals have two copies of chromosome 5, the normal chromosome does not compensate for the genetic material missing from the flawed chromosome in cri du chat syndrome. The deletion can be inherited through generations of a family or may appear at random. It is estimated that the...