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Cat eye syndrome (CES) or Schmid–Fraccaro syndrome is a rare condition caused by an abnormal extra
chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins ar ...
, i.e. a
small supernumerary marker chromosome A small supernumerary marker chromosome (sSMC) is an abnormal extra chromosome. It contains copies of parts of one or more normal chromosomes and like normal chromosomes is located in the cell's nucleus, is replicated and distributed into each d ...
. This chromosome consists of the entire short arm and a small section of the long arm of
chromosome 22 Chromosome 22 is one of the 23 pairs of chromosomes in human cells. Humans normally have two copies of chromosome 22 in each cell. Chromosome 22 is the second smallest human chromosome, spanning about 49 million DNA base pairs and representing ...
. In consequence, individuals with the cat eye syndrome have three ( trisomic) or four ( tetrasomic) copies of the genetic material contained in the abnormal chromosome instead of the normal two copies. The prognosis for patients with CES varies depending on the severity of the condition and their associated signs and symptoms, especially when heart or kidney abnormalities are seen.


Signs and symptoms

* Unilateral or bilateral
iris Iris most often refers to: *Iris (anatomy), part of the eye *Iris (mythology), a Greek goddess * ''Iris'' (plant), a genus of flowering plants * Iris (color), an ambiguous color term Iris or IRIS may also refer to: Arts and media Fictional ent ...
coloboma A coloboma (from the Greek , meaning defect) is a hole in one of the structures of the eye, such as the iris, retina, choroid, or optic disc. The hole is present from birth and can be caused when a gap called the choroid fissure, which is presen ...
(absence of tissue from the colored part of the eyes) * Preauricular pits/tags (small depressions/growths of skin on the outer ears) *
Anal atresia An imperforate anus or anorectal malformations (ARMs) are birth defects in which the rectum is malformed. ARMs are a spectrum of different congenital anomalies which vary from fairly minor lesions to complex anomalies. The cause of ARMs is unknow ...
(abnormal obstruction of the anus) * Downward-slanting
palpebral fissures The palpebral fissure is the elliptic space between the medial and lateral canthi of the two open eyelids. In simple terms, it is the opening between the eyelids. In adult humans, this measures about 10 mm vertically and 30 mm horizontally. Var ...
(openings between the upper and lower eyelids) *
Cleft palate A cleft lip contains an opening in the upper lip that may extend into the nose. The opening may be on one side, both sides, or in the middle. A cleft palate occurs when the palate (the roof of the mouth) contains an opening into the nose. The ...
* Kidney problems (missing, extra, or underdeveloped kidneys) * Short stature *
Scoliosis Scoliosis is a condition in which a person's spine has a sideways curve. The curve is usually "S"- or "C"-shaped over three dimensions. In some, the degree of curve is stable, while in others, it increases over time. Mild scoliosis does not ty ...
/skeletal problems * Cardiac defects (such as TAPVR) * Micrognathia (smaller jaw) *
Hernia A hernia is the abnormal exit of tissue or an organ, such as the bowel, through the wall of the cavity in which it normally resides. Various types of hernias can occur, most commonly involving the abdomen, and specifically the groin. Groin her ...
s * Biliary atresia * Rarer malformations can affect almost any organ *
Intellectual disability Intellectual disability (ID), also known as general learning disability in the United Kingdom and formerly mental retardation, Rosa's Law, Pub. L. 111-256124 Stat. 2643(2010). is a generalized neurodevelopmental disorder characterized by signif ...
– 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 In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological pr ...
symptoms Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showi ...
of the
syndrome A syndrome is a set of medical signs and symptoms which are correlated with each other and often associated with a particular disease or disorder. The word derives from the Greek language, Greek σύνδρομον, meaning "concurrence". When a sy ...
. This sSMC may be small, large, or ring-shaped, and typically includes 2 Mb, i.e. 2 million DNA
base pairs A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DN ...
, termed the CES critical region, located on its q arm(s) between its
band Band or BAND may refer to: Places *Bánd, a village in Hungary *Band, Iran, a village in Urmia County, West Azerbaijan Province, Iran * Band, Mureș, a commune in Romania *Band-e Majid Khan, a village in Bukan County, West Azerbaijan Province, I ...
11 and terminus (area notated as 22pter→q11)(also see small supernumerary marker chromosomes in cat eye syndrome). This area contains the ''
CECR1 Cat eye syndrome critical region protein 1 is a protein that in humans is encoded by the ''CECR1'' gene. This gene encodes a member of a subfamily of the adenosine deaminase protein family. The encoded protein may act as a growth factor and have ...
'', ''SLC25A18'', and ''
ATP6V1E1 V-type proton ATPase subunit E 1 is an enzyme that in humans is encoded by the ''ATP6V1E1'' gene. This gene encodes a component of vacuolar ATPase (V-ATPase), a multisubunit enzyme that mediates acidification of eukaryotic intracellular organelles ...
'' genes which are strong
candidate genes The candidate gene approach to conducting genetic association studies focuses on associations between genetic variation within pre-specified genes of interest, and phenotypes or disease states. This is in contrast to genome-wide association studies ...
for causing or promoting at least some of the birth defects in CES.


Diagnosis


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.


See also

* Trisomy 22


References


External links

{{Chromosomal abnormalities Congenital disorders Syndromes affecting stature Syndromes affecting the jaw Syndromes affecting the heart Syndromes affecting the kidneys Syndromes with cleft lip and/or palate Syndromes affecting the eye Rare syndromes