Chromosomal Basis of Inherited Disorders

Duplications and Deletions

In addition to losing or gaining an entire chromosome, a chromosomal segment may duplicate or lose itself. Duplications and deletions often produce offspring that survive but exhibit physical and mental abnormalities. Duplicated chromosomal segments may fuse to existing chromosomes or may be free in the nucleus. Cri-du-chat (from the French for “cry of the cat”) is a syndrome that occurs with nervous system abnormalities and identifiable physical features that result from a deletion of most 5p (the small arm of chromosome 5) (Figure). Infants with this genotype emit a characteristic high-pitched cry on which the disorder’s name is based.

 Photos show a boy with cri-du-chat syndrome. In parts a, b, c, and d of the image, he is two, four, nine, and 12 years of age, respectively.
This figure shows an individual with cri-du-chat syndrome at two, four, nine, and 12 years of age. (credit: Paola Cerruti Mainardi)