Cat eye syndrome: a rare genetic disorder

The term “cat eye syndrome” derives from a distinct eye abnormality that appears in some people with this disorder. This trait results from an absence of eye tissue, affecting both eyes.

The ocular defects can include an abnormal pupil color, defects to the middle layer of the eye, or damage to the optic nerve.

The disorder is caused by a chromosome defect that affects different organs, signs and symptoms vary but may include abnormalities of the eyes, ears, anus, heart, and kidneys. Most cases occur alternately among people without family history of this condition. Treatment focuses on relieving the symptoms.



Cat eye syndrome is caused by a defect in chromosome 22. This defect includes extra duplicates of the chromosome (trisomy or tetrasomy), or a chromosome inversion. People with cat eye syndrome have an additional copy of chromosome 22 (this can be known as a small supernumerary marker chromosome). The excess genetic material leads to the typical signs and symptoms.

People with abnormal chromosome structure have 2 copies of chromosome 22. However, many people with cat eye syndrome have an extra chromosome derived from two derivatives of chromosome 22. In these cases, the cells include four copies of the chromosome region instead of two.

Chromosome 22 duplication

The genetic material in the extra chromosome can appear in an inverted order to the normal chromosome 22, known as an inverted duplication. In some cases, this extra chromosome only appears in a certain percentage of cells, this condition is known as mosaicism or mosaic.



Signs and symptoms of CES vary but may include:

Eye pupil infections

Anal abnormalities and obstructions

Skin bruising

Abnormal ear form

Hearing loss

Hypertelorism (wide set eyes)

Downward slanting eye folds


Cleft palate

Heart birth defects

Urinary tract defects

Skeletal defects

Developmental delay

Mild to moderate intellectual disability



Cat eye syndrome diagnosis is based on suspicion arising after the presence of symptoms. 

Genetic testing can verify the diagnosis. These tests include:

Karyotype test – karyotype testing creates an imaging of the chromosomes.

FISH test – this lab technique identifies specific DNA sequences on a chromosome. During a FISH test, the chromosome is exposed to a small DNA sequence using an attached neon molecule. The revealed sequence attaches to the suitable sequence in the chromosome.


Prenatal testing

In some cases, a suspicion for cat eye syndrome arises before birth and is detected through prenatal tests such as ultrasound, amniocentesis, or chorionic villus sampling (CVS). During a fetal ultrasound, sound waves are used to create in image of the developing fetus that can reveal finding indicating a chromosome defect or other birth defects.

In amniocentesis, a sample of amniotic fluid (the fluid surrounding the fetus) is taken and tested. CVS Includes taking a small sample of the placenta. Chromosomal tests performed on these tissue or fluid samples can reveal cases of an extra or missing chromosome and identify cases of trisomy 22.


Cardiac assessment for detecting heart defects

A cardiac assessment is recommended for detecting heart defects. This assessment includes a thorough clinical examination, an assessment of the heart and lungs using a stethoscope, x-ray scans, echocardiogram, or cardiac catheterization. Electrocardiogram (ECG) results evaluates the heart’s electrical activity and can detect irregular patterns. In an echocardiogram, sound waves are directed at the heart to analyze the heart’s rhythm.

Cardiac catheterization is an insertion of a catheter into a large blood vessel leading to the heart. This procedure can help assess the function of the pumping chambers and measure pressure and oxygen content.

Eye and ear examinations – these tests can identify certain defects that can be linked to cat eye syndrome. They include eye examinations and hearing tests that help detect potential visual impairments or hearing loss to ensure efficient intervention and supporting treatment.


More diagnostic methods

Additional imaging technologies and tests can help identify gastrointestinal, urinary tract, kidney and skeletal defects, and more physical defects that can be associated with cat eye syndrome.

In addition, people with irregularly short stature that are affected by CES undergo laboratory tests that determine whether their growth delay is a result of a deficiency of growth hormones.



Because cat eye syndrome affects multiple organ systems, treatment is performed by a team of healthcare professionals and specialists. Treatment varies according to the signs and symptoms displayed by each patient.

For instance, heart defects, anal obstructions, a cleft palate, and skeletal defects may require surgery. Children with walking difficulties are referred to physical therapy and occupational therapy. Special education services are provided for children with intellectual disabilities.

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