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What is Cat Eye Syndrome?

Cat Eye Syndrome (CES), also known as Schmid-Fraccaro Syndrome, is a rare chromosomal disorder first documented in 1898. It was named accordingly because of a common phenotypic characteristic, ocular coloboma, where individuals have tissue missing from the colored part of the eyes. This gives the appearance of cat-like eyes. However, this characteristic is not present in all individuals with CES [1].

CES occurs due to the short arm (p) and the long arm (q) of chromosome 22 duplicating multiple times and being presented three (trisomic) or four times (tetrasomic) [3]. The exact nature of the duplications is still being researched at this time.

Phenotype Characteristics

Cat Eye Syndrome (CES) is characterized by high phenotypic variability. Individuals with CES range from having no perceivable phenotype to individuals with serious abnormalities. The following are a list of the more common phenotypic characteristics of patients with CES:

Less common characteristics include [2]:

  • Microphthalmia
  • Meckel’s Diverticulum
  • Hyperactive behaviour
  • Shortened height
  • Umbilical hernia
  • Hypogonadotropic hypogonadism

Only 41% of patients with CES have a combination of all three characteristics of iris coloboma, anal anomalies and pre-auricular anomalies. Therefore, diagnosis of CES cannot rely strictly on phenotypic characteristics and chromosomal investigation is required [1].

Probabilities and Risks Associated with CES

Cat Eye Syndrome is estimated to afflict 1 in 50,000 to 1 in 150,000 [3]. However as with the majority of genetic conditions a higher frequency is observed in families with a history of CES. This is not to say that CES will not occur in families with no prior history of CES.

  • If a child has CES, future siblings may also have CES due to the possibility of germline mosaicism. The approximate probability has not been published; however, it is deemed to be low [2].
  • Individuals with CES that are known to have the inverted duplication of chromosome 22 have a 50% chance of passing on CES to their offspring [2].


1. Berends MJ, Tan-Sindhunata G, Leegte B, van Essen AJ. Phenotypic variability of Cat-Eye syndrome. Genet Couns. 2001;12:23–34

2. Chen, H., Cat Eye Syndrome, Atlas of Genetic Diagnosis and Counselling. NY, NY: Springer US; 2012. p. 279, 280, 281.

3. Schinzel, A., W. Schmid, et al. (1981). “The “Cat Eye syndrome”: Dicentric small marker chromosome probably derived from a No. 22 (Tetrasomy 22pter→q11) associated with a characteristic phenotype.” Human Genetics 57(2): 148-158.

4. Win, T.N., Roberts, S., & Laws, D. (2007). Duane syndrome associated with the Cat Eye Syndrome: a case report. 21, April 20, 2012. 289-291.