What is Cat Eye Syndrome?

Cat eye syndrome (CES) is a rare congenital chromosomal disorder marked by various findings and results from a duplication of chromosome 22. Individuals with moderate dysmorphia to patients with severe abnormalities can all be diagnosed with CES. Characteristic features like iris colobomas, anorectal abnormalities, and preauricular anomalies affect about 40% of CES patients. Schachenmann et al. identified the genetic basis and mechanism of inheritance of CES for the first time in 1965.

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Causes and symptoms

Cat eye syndrome is a rare genetic condition caused by the short arm (p) and tiny region of the long arm (q) of chromosome 22 being duplicated three (trisomy) to four (tetrasomy) times instead of twice. The syndrome's name comes from the eye abnormalities that are commonly linked with it. Schmid Fraccaro syndrome, chromosome 22 partial trisomy/tetrasomy, and chromosome 22-inverted duplication are the different names for this condition.

Patients with cat eye syndrome might have a wide range of phenotypes, ranging from minor to severe abnormalities, making diagnostic clinical criteria difficult to establish. Patients usually have a triad of iris coloboma, anal atresia, and a preauricular skin tag or pit. However, Berends et al. observed in their study that just 41% of CES patients possessed the triad, implying that diagnosing nearly 60% of the patients could be challenging.

A high forehead, hypertelorism, epicanthus, and down slanting palpebral fissures are among the minor dysmorphias that have been recorded. Microphthalmia, cataract, strabismus, and Duane anomaly are some of the other ocular deformities mentioned. In severe cases, congenital cardiac abnormalities, kidney malformations, and gastrointestinal deformities have also been recorded. Although cognition is usually normal, 30% of patients have an intellectual disability.

Preauricular skin tags and pits are the most common otologic signs in the majority of individuals. Low set ears and microtia, as well as conductive or sensorineural hearing loss, may be present. In about 30% of cases, mild to moderate mental retardation is observed, with no evident phenotypic difference between mentally normal and mentally retarded CES patients.

Patients with almost normal phenotypes to those with severe abnormalities, including life-threatening congenital deformities, show a wide range of phenotypic variability with the syndrome. Anatomical asplenia, hemifacial microsomia, and Müllerian agenesis have all been recorded as unusual occurrences.

The CES chromosome

An extra bisatellited marker chromosome is present in cat eye syndrome. This leads to partial tetrasomy of euchromatic material from 22pter to 22q11. Breakpoints within band 22q11 create the usual CES chromosomes. A region that corresponds to the proximal breakpoint interval in the 22q11 deletion syndrome (DiGeorge/velocardiofacial syndrome) is the most prevalent breakpoint interval.

The smaller (type I) CES chromosomes are symmetrical, with both breakpoints in the proximal interval, whereas the larger (type II) CES chromosomes are either asymmetrical, with one breakpoint in each of the two intervals, or symmetrical, with both breakpoints in the distal interval, resulting in 1 or 2 extra copies of the DiGeorge critical region.

The fact that penetrance and clinical symptoms are unrelated to the amount of supernumerary euchromatic material is noteworthy. The extra chromosome 22 is normally inherited from one of the parents. The likelihood of a carrier's progeny inheriting the marker chromosome is roughly 50%.

Epidemiology

There was no exact estimate of the likelihood of cat eye syndrome occurrence until recently, presumably because patients with some or all of the accompanying symptoms and indications are infrequently identified with CES or go untreated entirely. In Northeastern Switzerland, Schinzel et al. calculated an incidence of 1:50,000 to 1:150,000 people, with no gender preference.

Diagnosis and treatment

As cat eye syndrome has such a wide phenotypic range and the potential to damage so many organ systems, the overall prognosis varies greatly, from those who have very minor abnormalities to those who have deadly presentations.

While the molecular size of the duplicated area varies depending on whether low copy repeat is the location of rearrangement, no link has been found between phenotypes and the size of chromosome 22 duplications. Karyotyping and FISH form the first line of diagnosis.

To diagnose all the different manifestations of this syndrome, a thorough examination is required. A definitive diagnosis allows for the assessment of systemic problems and proper genetic counseling regarding the likelihood of recurrence in future pregnancies.

A team of doctors and other healthcare professionals often provides medical management. Treatment for this ailment is determined by the indications and symptoms that each person exhibits. Congenital heart problems, anal atresia, cleft lip and/or palate, and skeletal anomalies, for example, may necessitate surgery.

Physical therapy or occupational therapy may be recommended for children who have not reached their motor milestones (such as walking). Children with intellectual disabilities frequently require special education assistance. Although some severely affected babies die during infancy, the majority of people with cat eye syndrome do not have a shorter life expectancy.

Unless they have serious symptoms, such as heart or kidney abnormalities, the majority of CES patients will have a normal life expectancy with proper care.

References:

• Katz, B., Enright, J., Couch, S., Harocopos, G., & Lee, A. R. (2020). Atypical presentation of Cat Eye Syndrome in an infant with Peters anomaly and microphthalmia with cyst. Ophthalmic genetics, 41(6), 645–649. https://doi.org/10.1080/13816810.2020.1814346
• Hernández-Medrano, C., Hidalgo-Bravo, A., Villanueva-Mendoza, C., Bautista-Tirado, T., & Apam-Garduño, D. (2021). Mosaic cat eye syndrome in a child with unilateral iris coloboma. Ophthalmic genetics, 42(1), 84–87. https://doi.org/10.1080/13816810.2020.1839918
• Alamer, L., Bassant, S., Alhazmi, R., & Alzahrani, M. (2019). Rare otologic presentation of cat eye syndrome. Annals of Saudi medicine, 39(6), 441–443. https://doi.org/10.5144/0256-4947.2019.441
• Alsat, E. A., Reutter, H., Bagci, S., Kipfmueller, F., Engels, H., Raff, R., Mangold, E., Gembruch, U., Geipel, A., Müller, A., & Schaible, T. (2018). Congenital diaphragmatic hernia in a case of Cat eye syndrome. Clinical case reports, 6(9), 1786–1790. https://doi.org/10.1002/ccr3.1646
• (2015). Cat Eye Syndrome. [Online] NIH- GARD. Available at: https://rarediseases.info.nih.gov/diseases/26/cat-eye-syndrome

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Written by

Emily Henderson

During her time at AZoNetwork, Emily has interviewed over 200 leading experts in all areas of science and healthcare including the World Health Organization and the United Nations. She loves being at the forefront of exciting new research and sharing science stories with thought leaders all over the world.