Cat eye syndrome is a rare chromosomal disorder that may be evident at birth. Individuals with a normal chromosomal make-up have two 22nd chromosomes, both of which have a short arm, known as 22p, and a long arm, called 22q. However, in individuals with cat eye syndrome, the short arm and a small region of the long arm of chromosome 22 (i.e., 22pter-22q11) are present three or four times (trisomy or tetrasomy) rather than twice in cells of the body.
The name "cat eye syndrome" is derived from a distinctive eye (ocular) abnormality that is present in some affected individuals. This feature consists of partial absence of ocular tissue (coloboma), often affecting both eyes (bilateral). Affected ocular tissues may include the colored region (iris), the middle layer (choroid), and/or the nerve-rich innermost membrane (retina) of the eye.
Associated symptoms and findings may vary greatly in range and severity, including among affected members of the same family. While some may have few or mild manifestations that may remain unrecognized, others may have the full spectrum of malformations. However, in many cases, characteristic features of the disorder include mild growth delays before birth; mild mental deficiency; and malformations of the skull and facial (craniofacial) region, the heart, the kidneys, and/or the anal region.
More specifically, individuals with cat eye syndrome frequently have coloboma(s), downslanting eyelid folds (palpebral fissures), widely spaced eyes (ocular hypertelorism), and/or other ocular defects; misshapen ears with abnormal outgrowths of skin and small depressions in front of the outer ears (preauricular tags and pits), and/or absence (atresia) of the anal canal, with an abnormal passage (fistula) from the end portion of the large intestine (rectum) into abnormal locations (e.g., the bladder, vagina, or perineum). Additional features may commonly include variable congenital heart (cardiac) defects, kidney (renal) abnormalities, skeletal defects, and/or other physical findings.
Although the symptoms and physical findings associated with cat eye syndrome may be extremely variable, such abnormalities tend to involve the eyes, ears, anal region, heart, and/or kidneys. However, as mentioned above, it is important to note that some affected individuals may manifest so few symptoms that they may never be diagnosed with the disorder.
Many individuals with cat eye syndrome have eye (ocular) abnormalities, such as absence of some ocular tissue from one or both eyes (unilateral or bilateral). The coloboma may involve the colored region (iris), the middle layer (choroid), and/or the nerve-rich innermost membrane (retina) of the eye. Iris coloboma may give the iris an unusual “keyhole” appearance. Although coloboma was originally considered a primary feature of the disorder, this abnormality is not present in all individuals with cat eye syndrome.
In many cases, affected individuals have additional eye abnormalities, such as downwardly slanting eyelid folds (palpebral fissures); vertical skin folds that may cover the inner corners of the eyes (epicanthal folds); widely spaced eyes (ocular hypertelorism), crossing of the eyes (strabismus); and/or abnormal smallness of one of the eyes (unilateral microphthalmia). Less frequently, other ocular defects may be present. These may include absence of the iris (aniridia); clouding of the dome-shaped, normally transparent region of the front of the eyeball (cornea); absence of tissue from portions of the eyelid (eyelid coloboma); loss of transparency of the lens of the eye (cataract), and/or Duane syndrome. The latter is a condition characterized by limitation or absence of certain horizontal eye movements and retraction or “drawing back” of the eyeball into the eye cavity (orbit) upon attempting to look inward. In some cases, depending on the severity and/or combination of eye abnormalities present, varying degrees of visual impairment may result.
Cat eye syndrome is also commonly associated with abnormalities of the ears. Affected individuals may have small outgrowths of skin and/or slight depressions in front of the outer ears (preauricular tags and/or pits). In addition, the outer portions of the ears (auricles) may be low set and malformed (dysplastic), with blind-ending or absent external ear canals (microtia). In most cases, absence (atresia) of the external ear canal tends to affect one ear and may cause mild hearing impairment due to inadequate transmission of sound from the external to the inner ear (conductive hearing loss).
Some individuals with cat eye syndrome may have additional malformations of the skull and facial (craniofacial) region. Such abnormalities may include an abnormally small lower jaw (mandibular hypoplasia), a flat nasal bridge, an abnormal groove in the upper lip (cleft lip), and/or incomplete closure of the roof of the mouth (cleft palate).
Cat eye syndrome may also be characterized by malformations of the gastrointestinal and/or genital and urinary (genitourinary) tracts. In some affected individuals, the anal opening may be unusually small or narrow or the anal canal may be absent (anal atresia), with a passage (fistula) from the end portion of the large intestine (rectum) into abnormal locations. In males, fistulae may form between the rectum and the muscular organ that collects urine (bladder), the tube that excretes urine from the bladder (urethra), or the area behind the genitals (perineum). In females, fistulae may be present between the rectum and the bladder or the vagina. Some affected males may also have undescended testes (cryptorchidism), in some females, there may be underdevelopment of the uterus or absence of the vagina.
In addition, in some individuals with the syndrome, portions of the intestine may protrude through a defect in the abdominal wall at the navel (umbilical hernia) or into the canal that passes through lower muscular layers of the abdominal wall (inguinal hernia). (In males, the inguinal canal is the tubular passageway through which the testes normally descend from the abdomen into the scrotum before birth.) Additional reported features have included an abnormal saclike protrusion (Meckel diverticulum) from the lower small intestine (ileum), incomplete rotation of the upper large intestine (cecum), and/or absence of groups of nerve fibers (ganglia) in the muscular wall of the large intestine (Hirschsprung’s disease), resulting in impairment or absence of the involuntary, rhythmic contractions (peristalsis) that propel waste materials through the lower digestive tract. Associated findings may include an abnormal accumulation of feces within the colon, widening of the colon above the affected segment (megacolon), abdominal bloating, periodic vomiting, loss of appetite (anorexia), and/or other abnormalities. (For more information, use “Hirschsprung*” as your search term in the Rare Disease Database.)
Some individuals with cat eye syndrome may also have structural abnormalities of the heart at birth (congenital heart defects), particularly total anomalous pulmonary venous return or tetralogy of Fallot. Associated symptoms and findings may vary, depending on the size, nature, and/or combination of heart malformations present and other factors.
Tetralogy of Fallot consists of a combination of cardiac defects. These include an abnormal opening in the partition (septum) separating the two lower chambers of the heart (ventricular septal defect); obstruction of the proper outflow of blood from the right ventricle to the lungs due to narrowing of the opening between the ventricle and the pulmonary artery (pulmonary stenosis), displacement of the aorta, enabling oxygen-depleted blood to flow from the right ventricle to the aorta; and thickening (hypertrophy) of heart muscle of the right ventricle. (The pulmonary artery transports oxygen-depleted blood from the right ventricle to the lungs, where the exchange of oxygen and carbon dioxide occurs. The aorta, the major artery of the body, arises from the left ventricle and supplies oxygen-rich blood to most arteries.) Associated symptoms and findings may include insufficient oxygen supply to body tissues (hypoxia), bluish discoloration of the skin and mucous membranes (cyanosis), shortness of breath (dyspnea), feeding difficulties, failure to grow and gain weight at the expected rate (failure to thrive), and/or other abnormalities. (For more information on this disorder, choose “tetralogy of Fallot” as your search term in the Rare Disease Database.)
Total anomalous pulmonary venous return (TAPVR) is characterized by abnormalities in blood flow to the heart. The pulmonary veins normally return oxygenated blood from both lungs to the left upper chamber (left atrium) of the heart. However, in infants with TAPVR, the pulmonary veins improperly return blood directly to the upper right chamber (right atrium) of the heart or to veins draining into the right atrium, leading to mixing of oxygenated and oxygen-deficient blood. Associated symptoms and findings may include cyanosis, abnormally rapid breathing (tachypnea), rising blood pressure in the lungs (pulmonary hypertension), inability of the heart to pump enough blood to meet the body’s requirements for oxygen (heart failure), and/or other abnormalities. In severe cases, congenital heart disease may lead to potentially life-threatening complications.
Various kidney (renal) malformations are also frequently associated with cat eye syndrome. Such renal abnormalities may include underdevelopment and/or absence of one or both kidneys (unilateral or bilateral renal hypoplasia and/or agenesis); the presence of an additional kidney (supernumerary kidney); abnormal swelling (distention) of and accumulation of urine in the kidneys (hydronephrosis); and/or abnormal development of renal cysts (cystic dysplasia). Associated symptoms and findings depend upon the range and/or severity of renal malformations present.
In addition, in some individuals with cat eye syndrome, bile ducts may fail to develop or develop abnormally (biliary atresia). Bile, a liquid secreted by the liver, plays an essential role in carrying waste products from the liver and breaking down fats in the small intestine. The bile ducts are narrow tubes through which bile passes from the liver to the first section of the small intestine (duodenum). Due to such absence or underdevelopment of bile ducts, bile is unable to reach the intestine and abnormally accumulates in the liver. Associated findings may include yellowing of the skin, mucous membranes, and whites of the eyes (jaundice); abnormally dark urine; pale feces; enlargement of the liver; growth failure; and/or additional symptoms. Without appropriate treatment, scarring and impaired functioning of the liver may lead to potentially life-threatening complications. (For more information, choose “biliary atresia” as your search term in the Rare Disease Database.)
Many individuals with cat eye syndrome may also have growth delays during fetal development (mild prenatal growth retardation). In addition, reports suggest that short stature appears to be a common finding. Investigators indicate that affected individuals with severe short stature may lack sufficient levels of a hormone that stimulates normal growth and development (growth hormone), possibly due to improper function of the hypothalamus and associated, diminished activity of the gland that secretes growth hormone (pituitary gland).
Affected individuals may also have additional skeletal abnormalities. These may include abnormal sideways curvature of the spine (scoliosis); abnormal fusion of certain bones in the spinal column (vertebral fusions); absence of the bone on the thumb side of the forearm (radial aplasia); absence or abnormal fusion (synostosis) of certain ribs; absence of certain toes and/or duplication of the large toes (hallux); and/or dislocation of the hips.
Some individuals with cat eye syndrome have normal intelligence. However, many have borderline normal to mild mental retardation, or, less commonly, moderate retardation. Rare cases of severe mental retardation have also been reported.
Cat eye syndrome is a rare disorder associated with the presence of an extra chromosome fragment, in which the short arm (p) and a small portion of the long arm (q) of chromosome 22 are present three or four times (trisomy or tetrasomy) rather than twice in cells of the body.
Chromosomes are found in the nucleus of all body cells. They carry the genetic characteristics of each individual. Pairs of human chromosomes are numbered from 1 through 22, with an unequal 23rd pair of X and Y chromosomes for males and two X chromosomes for females. Each chromosome has a short arm designated as “p,” a long arm identified by the letter “q,” and a narrowed region at which the two arms are joined (centromere). Chromosomes are further subdivided into bands that are numbered outward from the centromere. For example, the short arm of chromosome 22 includes bands 22p11.1 to 22p13; the end or “terminal” of the short arm is known as 22pter. The long arm includes bands 22q11.1 to 22q13.
Thus, individuals with a normal chromosomal make-up (karyotype) have two 22nd chromosomes, both of which consist of a short arm (22p), a long arm (22q), and a centromere. However, many individuals with cat eye syndrome have an extra chromosome (supernumerary bisatellited marker chromosome). This marker chromosome is derived from two segments of chromosome 22, which consist of the short arm, the centromere (i.e., dicentric), and a piece of the long arm (22q11); therefore, in such cases, this chromosomal region (22pter-22q11) is present in cells of the body four times (tetrasomic) rather than the normal two. The material within the supernumerary chromosome may appear in the reverse order of that within the normal 22nd chromosome (i.e., inverted duplication). In addition, in many cases, this extra chromosome may be present in only a certain percentage of the body’s cells (known as mosaicism).
In other cases, the chromosomal segment from 22pter to band q11 may appear three times (trisomy) rather than twice in cells of the body. Researchers indicate that trisomy or tetrasomy of a region within proximal 22q11 is critical for expression of all or most of the features associated with cat eye syndrome. This region is referred to as the critical CES (cat eye syndrome) region. (Proximal indicates closer to or nearest a particular point of reference [i.e., the centromere].) Research is ongoing to isolate and characterize the gene(s) responsible for features associated with cat eye syndrome.
The exact cause of cat eye syndrome is not fully understood. In some instances, the chromosomal abnormality appears to arise “de novo” or randomly (sporadically) due to an error in the division of a parent’s reproductive cells (meiotic error); in such cases, the parent has normal chromosomes. In others, it may appear to result from a balanced translocation in one of the parents. Translocations occur when portions of certain chromosomes break off and are rearranged, resulting in shifting of genetic material and an altered set of chromosomes. If a chromosomal rearrangement is balanced, meaning that it consists of an altered but balanced set of genes, it is usually harmless to the carrier. However, such a chromosomal rearrangement may be associated with an increased risk of abnormal chromosomal development in the carrier’s offspring.
In other cases, a parent of an affected child may have the marker chromosome in some body cells (mosaicism) and, in some instances, manifest certain, possibly mild features of the disorder. Evidence indicates that mosaicism for this chromosomal abnormality may be transmitted through several generations in some families; however, as noted above, expression of associated features may be variable. As a result, only those with multiple or severe features may be identified.
Some researchers suggest that certain regions of 22q11 are susceptible to chromosomal instability and chromosomal rearrangements associated with certain congenital malformation disorders, including cat eye syndrome. Such investigators indicate that the basic underlying defect for the syndrome may be inherited fragile chromosomal sites or other possible predispositions that may lead to complex rearrangements seen in cat eye syndrome.
Chromosomal analysis and genetic counseling may be recommended for parents of an affected child to help confirm or exclude the presence of certain abnormalities involving chromosome 22 (e.g., mosaicism for the marker chromosome, balanced translocation) and evaluate recurrence risk.
Further research is necessary to learn more about the complex chromosomal and genetic mechanisms potentially responsible for the expression and transmission of the syndrome.
As mentioned above, cat eye syndrome is named for coloboma of the eye, an often bilateral finding in some affected individuals. The syndrome has been recognized for more than a century. The presence of coloboma occurring along with anal atresia (see “Symptoms” above) was initially considered primary features of the syndrome. However, cat eye syndrome was more specifically defined in 1965, when researchers reported that some affected individuals have only one or neither of these features. The diagnosis is currently based on the presence of extra chromosomal material derived from chromosome 22 (i.e., containing the critical CES region). (For further information, see “Causes” above.)
More than 100 cases have been reported in the medical literature, including apparently sporadic and familial cases. According to researchers, there are no specific estimates concerning the incidence of the chromosomal marker for cat eye syndrome in the general population. (Incidence refers to the number of new cases of a particular disorder or condition during a specific period.) Yet, based on affected individuals observed in Northeastern Switzerland in the last two decades, investigators estimate an incidence of approximately one in 50,000 to one in 150,000 individuals. Because some affected individuals develop few associated features, however, the disorder may often remain unrecognized and may therefore be underdiagnosed, making it difficult to determine the true frequency of cat eye syndrome in the general population.
In some cases, it is possible that a diagnosis of cat eye syndrome may be suspected before birth (prenatally) based upon specialized tests, such as ultrasound, amniocentesis, and/or chorionic villus sampling (CVS). During fetal ultrasonography, reflected sound waves create an image of the developing fetus, potentially revealing certain findings that suggest a chromosomal disorder or other developmental abnormalities. During amniocentesis, a sample of fluid that surrounds the developing fetus is removed and analyzed, while CVS involves the removal of tissue samples from a portion of the placenta. Chromosomal studies performed on such fluid or tissue samples may reveal tetrasomy (supernumerary chromosome) or trisomy of a portion of chromosome 22.
In some cases, cat eye syndrome is recognized or confirmed after birth (postnatally) by a thorough clinical evaluation, detection of characteristic physical findings, standard chromosomal studies, and specialized tests to identify specific DNA sequences (e.g., fluorescence in situ hybridization [FISH]). The diagnosis is based on detection of extra chromosomal material containing the critical CES region (see "Causes" above). According to reports in the medical literature, characteristic features that may be helpful for diagnosis include coloboma, downslanting eyelid folds (palpebral fissures), preauricular tags and/or pits, malformed ears with absence of the external ear canal, anal atresia, heart defects, and renal malformations.
Various specialized tests may also be performed to help detect and/or characterize certain abnormalities that may be associated with the disorder, including thorough eye examination and careful monitoring of hearing. Early recognition of potential visual impairment and/or hearing loss may play an essential role in ensuring prompt intervention and appropriate, early correction or supportive treatment. In addition, a thorough cardiac evaluation may be advised to detect any heart abnormalities that may be present. Such evaluation may include a thorough clinical examination, evaluation of heart and lung sounds through use of a stethoscope, x-ray studies, electrocardiography (EKG), echocardiography, cardiac catheterization, and/or other cardiac studies. An EKG, which records the electrical activities of heart muscle, may reveal abnormal electrical patterns. During an echocardiogram, sound waves are directed toward the heart, enabling physicians to study cardiac function and motion. When cardiac catheterization is performed, a small hollow tube (catheter) is inserted into a large vein and threaded through the blood vessels leading to the heart. This procedure can be used for various purposes, including evaluating the pumping ability of the heart, measuring blood pressure within the heart, and withdrawing blood to measure oxygen content.
Additional specialized imaging techniques and/or other tests may also be used to detect and/or characterize certain gastrointestinal, genitourinary, renal, skeletal, biliary, and/or other physical abnormalities that may occur in association with cat eye syndrome. In addition, in affected individuals with severe short stature, laboratory testing and other studies may be conducted to help determine whether growth hormone deficiency may play a role in growth delays.
The treatment of cat eye syndrome may require the coordinated efforts of a team of medical professionals, such as pediatricians; surgeons; heart specialists (cardiologists); physicians who specialize in diagnosing and treating abnormalities of the digestive tract; eye specialists; health professionals who detect, evaluate, and help to manage hearing problems; physicians who diagnose and treat disorders of the skeleton, muscles, joints, and related tissues (orthopedists); and/or other health care professionals.
Disease management is directed toward the specific symptoms that are apparent in each individual. For those with congenital heart defects, treatment with certain medications, surgical intervention, and/or other measures may be required. In addition, surgical correction is necessary for anal atresia. In some cases, recommended treatment may also include surgical repair, correction, or management of certain ocular defects, skeletal abnormalities, genital defects, hernias, Hirschsprung's disease, biliary atresia, and/or other malformations associated with the disorder. The specific surgical procedures performed may depend upon the size, nature, severity, and/or combination of anatomical abnormalities; their associated symptoms; patient age; and other factors.
Before and after surgery for certain cardiac defects, individuals may be susceptible to bacterial infection of the heart lining and valves (endocarditis). Therefore, preventive (prophylactic) antibiotic therapy may be prescribed before and after certain surgical procedures and dental visits. In addition, respiratory infections must be treated vigorously and early.
For individuals with certain skeletal abnormalities, treatment may include physical therapy and various orthopedic techniques, potentially including surgical measures. In addition, as noted above, individuals with severe short stature in association with growth hormone deficiency may be candidates for growth hormone therapy.
Early intervention is important to ensure that children with cat eye syndrome reach their potential. Special services that may be beneficial include special remedial education, special social support, and/or other medical, social, and/or vocational services.
Genetic counseling will also be of benefit for patients and their families. As mentioned previously, chromosomal studies may be recommended for parents of affected individuals, such as to determine whether they exhibit mosaicism for the marker chromosome, particularly should they manifest any features that may be associated with the disorder (e.g., preauricular pits and/or tags, downslanting palpebral fissures). In other cases, chromosomal studies may help to determine whether a balanced translocation is present in one of the parents. Other treatment for this disorder is symptomatic and supportive.
Research is currently underway to determine whether there is a connection between the size of a person’s cat eye syndrome chromosome and the number and severity of symptoms the person shows. For more information, contact:
Heather McDermid, Professor
Department of Biological Sciences
University of Alberta
T6G 2E9 Canada
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
TTY: (866) 411-1010
For information about clinical trials sponsored by private sources, contact:
(Please note that some of these organizations may provide information concerning certain conditions potentially associated with this disorder [e.g., ocular abnormalities, anal atresia, biliary atresia, congenital heart abnormalities, short stature, mental retardation, etc.].)
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Online Mendelian Inheritance in Man, OMIM (TM). John Hopkins University, Baltimore, MD. MIM Number 115470; 7/13/00. Available at: http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?115470.
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