What is Cat Eye Syndrome?

Cat’s eye syndrome (CES) is a rare congenital chromosomal disorder characterized by various findings and results from a duplication of chromosome 22. People with moderate dysmorphism to patients with severe abnormalities can all be diagnosed with CES . Features such as iris colobomas, anorectal abnormalities, and preauricular abnormalities affect approximately 40% of patients with CES. Schachenman et al. first identified the genetic basis and transmission mechanism of CES in 1965.

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Causes and Symptoms

Cat’s eye syndrome is a rare genetic disorder caused by the duplication of the short arm (p) and the small region of the long arm (q) of chromosome 22 three (trisomy) to four (tetrasomy) times instead of of them. The name of the syndrome comes from the ocular abnormalities that are often associated with it. Schmid Fraccaro syndrome, partial trisomy/tetrasomy of chromosome 22, and inverted duplication of chromosome 22 are the different names for this condition.

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

A high forehead, hypertelorism, epicanthus and downward sloping palpebral fissures are among the minor dysmorphisms that have been recorded. Microphthalmia, cataract, strabismus and Duane’s anomaly are some of the other eye defects mentioned. In severe cases, congenital heart defects, kidney defects and gastrointestinal malformations have also been recorded. Although cognition is generally normal, 30% of patients have intellectual disability.

Skin tags and preauricular dimples are the most common otological signs in the majority of individuals. Low-set ears and microtia, as well as conductive or sensorineural hearing loss, may be present. In approximately 30% of cases, mild to moderate mental retardation is observed, with no obvious phenotypic difference between mentally normal and mentally retarded CES patients.

Patients with nearly normal phenotypes to those with severe abnormalities, including life-threatening birth defects, show a wide range of phenotypic variability with the syndrome. Anatomical asplenia, hemifacial microsomia, and Müller’s agenesis were all recorded as unusual events.

The CES chromosome

An additional bisatellite marker chromosome is present in cat’s eye syndrome. This leads to partial tetrasomy of euchromatic material from 22pter to 22q11. The breakpoints in the 22q11 band create the usual CES chromosomes. A region that corresponds to the proximal breakpoint interval in 22q11 deletion syndrome (diGeorge/velocardiofacial syndrome) is the most prevalent breakpoint interval.

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

The fact that penetrance and clinical symptoms are not related to the amount of supernumerary euchromatic material is remarkable. The extra chromosome 22 is normally inherited from one of the parents. The probability that the offspring of a carrier will inherit the marker chromosome is about 50%.

Epidemiology

There was no exact estimate of the likelihood of occurrence of cat eye syndrome until recently, probably because patients with some or all of the accompanying symptoms and indications are rarely identified with CES or are not fully addressed. 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

Because cat’s eye syndrome has such a wide phenotypic range and the potential to damage so many organ systems, the overall prognosis varies widely, from those with very minor abnormalities to those with life-threatening presentations.

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

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

A team of doctors and other health professionals often provide medical care. The treatment of this disease is determined by the indications and symptoms that each person presents. Congenital heart problems, anal atresia, cleft lip and/or palate, and skeletal abnormalities, for example, may require surgery.

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

Unless they have severe 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, AR (2020). Atypical presentation of cat’s 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’s 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. and Alzahrani, M. (2019). Rare otological presentation of cat’s eye syndrome. Annals of Saudi Medicine, 39(6), 441–443. https://doi.org/10.5144/0256-4947.2019.441
  • Alsat, EA, 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’s 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

Further reading

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