Barrett syndrome

Definition

Cri du chat syndrome arises from the absence of a particular portion of chromosome 5. The absence of genetic material is called a deletion. Children born with this deletion in chromosome 5 have a characteristic mewing cry as newborns that is thought to be caused by abnormal development of the larynx (the organ containing the vocal chords). For this reason, the disorder is called cri du chat (or cat's cry) syndrome. In reference to the deletion and the area where it occurs, the disorder is also called 5p- (5 p minus) syndrome. Children with this syndrome have physical abnormalities, language and motor skill difficulties, and varying degrees of mental retardation. Cri du chat syndrome is a very rare disorder.

Description

The original genetic material is arranged into 23 pairs of chromosomes--one set of 23 chromosomes is inherited from each parent. Using a microscope, distinct chromosomes can be seen at a certain point in a cell's life cycle. When treated with certain stains, each chromosome bears a typical banding pattern, reminiscent of the stripes on a tabby cat's tail. Using each chromosomes' unique size and banding pattern, chromosomes 1-22 and the sex chromosomes, X and Y, can be identified exactly.

Although all individuals have two copies of chromosome 5, the normal chromosome does not compensate for the genetic material missing from the flawed chromosome. The deletion can be inherited through generations of a family or it may appear at random. It has been estimated that the syndrome occurs in 1 in 50,000 births. According to the 5p- Society, approximately 50-60 children are born with cri du chat syndrome each year in the United States.

Causes & symptoms

The deletion on chromosome 5 has several indicators. The primary sign is an infant's high-pitched mewing cry during the first weeks of life. This unusual cry is accompanied by low birth weight, slow growth, and a small head (microcephaly). Muscle tone is poor (hypotonia) and possible medical problems include heart disease and scoliosis (curvature of the spine). Children with cri du chat syndrome have language difficulties, delayed motor skill development, and mental deficiencies that vary in severity. Behavioral problems, such as hyperactivity, may become apparent as the child matures.

Diagnosis

The key indicator of cri du chat syndrome is the characteristic catlike cry of an infant. As the child matures, this typical sound is lost. A definitive diagnosis is based on karyotyping. This laboratory procedure involves separating the chromosomes from a sample of the infant's cells. The chromosomes are then stained and examined under a microscope. The stain makes changes in the expected appearance of chromosome 5 noticeable and demonstrates that genetic material is missing. Cri du chat syndrome can be detected before birth if the mother undergoes amniocentesis testing or chorionic villus sampling. The samples of cells are collected from the fluid surrounding the fetus and are analyzed for genetic defects (amniocentesis test) or from the outer membrane (chorion) of the sac that holds both the fetus and the fluid (chorionic villus sampling test).

Treatment

There is no cure for cri du chat syndrome. Treatment consists of supportive care and developmental therapy.

Prognosis

The extent of mental retardation and other symptoms depends on the size of the chromosomal deletion--larger deletions generally translate into more serious symptoms. With intensive early intervention and special schooling, many cri du chat children can develop adequate social, motor, and language skills. Most individuals with cri du chat syndrome have a normal lifespan.

Prevention

Based on current knowledge, cri du chat syndrome cannot be prevented.

Key Terms

Aminocentesis

A procedure in which a needle is inserted through a pregnant woman's abdomen and into her uterus to withdraw a small sample of amniotic fluid. The amniotic fluid can be examined for signs of disease or other problems afflicting the fetus.

Chorionic villus sampling

A medical test that is best done during weeks 10-12 of a pregnancy. The procedure involves inserting a needle into the placenta and withdrawing a small amount of the chorionic membrane for analysis.

Chromosome

A structure composed of DNA contained within a cell's nucleus (center). The individual genetic material is stored in the chromosomes. Humans have 23 pairs of chromosomes, each of which has recognizable characteristics (such as length and staining patterns) that allow individual chromosomes to be identified. Identification is assigned by number (1-22) or letter (X or Y).

Deletion

The absence of genetic material that is normally found in a chromosome. Often, the genetic material is missing due to an error in replication of an egg or sperm cell.

Karyotyping

A laboratory procedure in which chromosomes are separated from cells, stained and arranged in order from the largest to the smallest so that their number and structure can be studied under the microscope. Any abnormality, such as a missing part of chromosome 5 in babies with Cri du chat, would be noticed with this test.

Further Reading

For Your Information

Books

• Gardner, R.J. McKinlay, and Grant R. Sutherland. Chromosome Abnormalities and Genetic Counseling. New York: Oxford University Press, 1996.
• Jones, Kenneth Lyons. Smith's Recognizable Patterns of Human Malformation, 5th ed. Philadelphia: W.B. Saunders Company, 1997.

  Organizations

• 5p- Society. (888) 970-0777. http://www.fivepminus.org/.

  Other

• Cri du Chat Booklet. Available for $10 from Medical College of Virginia, Department of Human Genetics, P.O. Box 980033, Richmond, VA 23298-0033. (804) 828-8116.

Gale Encyclopedia of Medicine. Gale Research, 1999.