Cat Eye Syndrome

Caused by Genetic Defect in Chromosome 22

Close up of woman's eye.
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Cat eye syndrome, named after how it affects the appearance of the eyes, is caused by a genetic defect in chromosome 22. There is a wide range of symptoms associated with the syndrome. Cat eye syndrome affects both males and females, and is estimated to occur in 1 in 74,000 individuals. Many individuals born with the syndrome are the only ones in their families who have it.

Symptoms of Cat Eye Syndrome

About 41 percent of individuals with cat eye syndrome have three symptoms in common:

  • absence of tissue from the colored part of one or both eyes (iris coloboma)
  • small growths of skin (tags) or depressions in the skin (pits) of the outer ears
  • an absence or obstruction of the anus (anal atresia)

In addition, individuals with cat eye syndrome may have:

  • congenital heart defect
  • downward slanting openings between the upper and lower eyelids
  • defects of the urinary tract or kidneys
  • short stature
  • cleft palate

Many other less common birth defects have been noted in individuals with cat eye syndrome.

Causes of Cat Eye Syndrome

The exact cause of cat eye syndrome is not fully understood, according to the National Organization for Rare Disorders. In some cases, the chromosomal abnormality appears to arise randomly due to an error in the division of a parent’s reproductive cells. In these cases, the parent has normal chromosomes. In others, it may appear to result from a balanced translocation in one of the parents.

Translocations occur when portions of certain chromosomes break off and are rearranged, resulting in shifting of genetic material and an altered set of chromosomes. If a chromosomal rearrangement is balanced, meaning that it consists of an altered but balanced set of genes, it is usually harmless to the carrier.

However, such a chromosomal rearrangement may be associated with an increased risk of abnormal chromosomal development in the carrier’s offspring.

In other cases, a parent of an affected child may have the marker chromosome in some body cells and, in some instances, manifest certain, possibly mild features of the disorder. Evidence indicates that this chromosomal abnormality may be transmitted through several generations in some families; however, as noted above, expression of associated features may be variable. As a result, only those with multiple or severe features may be identified.

Some researchers suggest that certain regions of the chromosome are susceptible to chromosomal instability and chromosomal rearrangements associated with certain congenital malformation disorders, including cat eye syndrome. Such investigators indicate that the basic underlying defect for the syndrome may be inherited fragile chromosomal sites or other possible predispositions that may lead to complex rearrangements seen in cat eye syndrome.

Chromosomal analysis and genetic counseling may be recommended for parents of an affected child to help confirm or exclude the presence of certain abnormalities involving chromosome 22 and evaluate recurrence risk.

Diagnosing Cat Eye Syndrome

Since cat eye syndrome is inherited, a child is born with it. Diagnosis is usually based on the symptoms present. Genetic testing can confirm the presence of the specific genetic defect in chromosome 22 (tripling or quadrupling of parts of the chromosome) that is associated with the syndrome.

Treating Cat Eye Syndrome

Treatment of cat eye syndrome focuses on the symptoms the individual has. Some children may need surgery to repair birth defects in the anus or heart. Life expectancy is not significantly reduced in those individuals who do not have life-threatening physical problems (such as a severe heart defect).


“Cat Eye Syndrome.” Chromosome 22 Central. Chromosome 22 Central Inc. 11 Apr 2007 <>.

Godinho, R.N., I.J. Keogh, G.M. Morales, N. Calixto, & T.M. Gonsalves. "Partial tetrasomy of chromosome 22: genetic and surgical implications for otolaryngologists." Ear Nose Throat Journal 83(2004): 748, 750, 752.

National Organization for Rare Disorders (NORD). Cat Eye Syndrome.

Schinzel, A., W. Schmid, M. Fraccaro, L. Tiepolo, O. Zuffardi, J.M. Opitz, J. Lindsten, P. Zetterqvist, H. Enell, C. Baccichetti, R. Tenconi, & R.A. Pagon. "The "cat eye syndrome": dicentric small marker chromosome probably derived from a no.22 (tetrasomy 22pter to q11) associated with a characteristic phenotype. Report of 11 patients and delineation of the clinical picture." Human Genetics 57(1981): 148-158.

Turleau, C. "Cat-eye syndrome." OrphaNet. Dec 2005. OrphaNet. 11 Apr 2007 <>.

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