Cat eye syndrome

Signs and symptoms

• Unilateral or bilateral iris coloboma (absence of tissue from the colored part of the eyes)
• Preauricular pits/tags (small depressions/growths of skin on the outer ears)

• Anal atresia (abnormal obstruction of the anus)
• Downward-slanting palpebral fissures (openings between the upper and lower eyelids)
• Cleft palate
• Kidney problems (missing, extra, or underdeveloped kidneys)
• Short stature
• Scoliosis/skeletal problems
• Cardiac defects (such as TAPVR)
• Micrognathia (smaller jaw)
• Hernias
• Biliary atresiaCongenital bile duct anomalies (biliary atresia) and chromosome 22 aneuploidy. Allotey J, Lacaille F, Lees MM, Strautnieks S, Thompson RJ, Davenport M. J Pediatr Surg. 2008 Sep;43(9):1736-40. doi: 10.1016/j.jpedsurg.2008.05.012.
• Rarer malformations can affect almost any organ
• Intellectual disability – many are intellectually normal; about 30% of CES patients have moderately impaired mental development, although severe intellectual disability is rare.

The term "cat eye" syndrome was coined because of the particular appearance of the vertical colobomas in the eyes of some patients, but over half of the CES patients in the literature do not present with this trait.

Genetics

The small supernumerary marker chromosome (sSMC) in CES usually arises spontaneously. It may be hereditary and parents may be mosaic for the marker chromosome, but show no phenotypic symptoms of the syndrome. This sSMC may be small, large, or ring-shaped, and typically includes 2 Mb, i.e. 2 million DNA base pairs, termed the CES critical region, located on its q arm(s) between its band 11 and terminus (area notated as 22pter→q11)(also see small supernumerary marker chromosomes in cat eye syndrome). This area contains the CECR1, SLC25A18, and ATP6V1E1 genes which are strong candidate genes for causing or promoting at least some of the birth defects in CES.

Diagnosis

An ultrasound exam may be used by a doctor to detect a birth defect that might be CES before a baby is born. An ultrasound creates an image of the fetus using sound waves. It might uncover specific CES-specific flaws. A follow-up test, like an amniocentesis, may be ordered by the doctor if they see these characteristics on an ultrasound. The doctor collects an amniotic fluid sample for analysis during amniocentesis. Extra chromosomal material from chromosome 22q11 helps doctors identify CES. The diagnosis can be verified through genetic testing. These tests could consist of:

• Karyotyping. A picture of a person's chromosomes is generated by this test.
• FISH, or fluorescence in situ hybridization. It is able to identify and pinpoint a particular DNA sequence on a chromosome.

The healthcare provider will likely order more testing when CES is identified to look for any potential extra problems, like heart or kidney disorders. These tests may include:

• X-rays and other imaging tests
• electrocardiography (EKG)
• echocardiography
• eye examination
• hearing tests
• cognitive function tests

History

The abnormalities common to CES were first cataloged in 1899, and described in association with a small marker chromosome in 1965. Early reports of CES discuss the possibility of chromosome 13 involvement. Now, CES is considered to be present with the chromosome 22 trisomy findings.

References

References

1. "Cat eye syndrome".
2. (2015). "Small supernumerary marker chromosomes and their correlation with specific syndromes". Advanced Biomedical Research.
3. (2001). "Phenotypic variability of the cat eye syndrome. Case report and review of the literature". Genet. Couns..
4. "Cat eye syndrome | Genetic and Rare Diseases Information Center (GARD) – an NCATS Program".
5. (18 July 2017). "Disorders of chromosome 22: Cat Eye Syndrome/Schmid Fraccaro Syndrome". Chromosome 22 Central.
6. "Cat eye syndrome {{!}} Genetic and Rare Diseases Information Center (GARD) – an NCATS Program".
7. (December 2020). "Prenatal diagnosis and molecular cytogenetic identification of small supernumerary marker chromosomes: analysis of three prenatal cases using chromosome microarray analysis". Aging.
8. (September 2012). "A 600 kb triplication in the cat eye syndrome critical region causes anorectal, renal and preauricular anomalies in a three-generation family". European Journal of Human Genetics.
9. Haab, O. Albrecht v Graefes. [[Archives of Ophthalmology]], 24: 257 only, 1879
10. Schachenmann G.. (1965). "Chromosomes in Coloboma and Anal Atresia". Lancet.
11. (1972). "Cat-eye syndrome, a partial trisomy 22". Humangenetik.