What is cat eye syndrome
Cat eye syndrome is a rare chromosomal disorder with a highly variable clinical presentation that may be evident at birth 1. Cat eye syndrome signs and symptoms vary widely but may include abnormalities of the eyes, ears, anal region, heart and/or kidney. Most cat eye syndrome patients have multiple malformations affecting the eyes (iris coloboma), ears (preauricular pits and/or tags), anal region (anal atresia), heart and kidneys. Intellectual disability is usually mild or borderline normal. Cat eye syndrome has an estimated prevalence of 1/50,000 to 1/150,000 live births 1. Males and females appear to be affected equally 1. More than 100 cases have been described in the medical literature, including apparently sporadic and familial cases. Many more affected individuals exist but have not been described in the medical literature. However, the syndrome is very rare, and currently there are no accurate estimates of the incidence of cat eye syndrome in the population. Schinzel et al 2 estimated an incidence of approximately one in 50,000 to one in 150,000 individuals in Northeastern Switzerland. Because some affected individuals develop few associated features, however, the disorder may in some people remain unrecognized. There is currently no way to estimate how underdiagnosed cat eye syndrome is.
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, known as 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 four times (partial tetrasomy) rather than twice in cells of the body. In a small number of people with cat eye syndrome, the 22q11 region is present in 3 copies (partial trisomy). The name “cat eye syndrome” is derived from a distinctive eye (ocular) abnormality that is present in a little over half affected individuals. This defect, known as a coloboma, usually appears as a cleft or gap in the iris below the pupil, and the elongated pupil therefore resembles the appearance of a cat’s eye. There are, however, many other features associated with cat eye syndrome involving many organs and systems. These symptoms result from abnormal development during embryo and fetal stages. Associated symptoms vary greatly in presence and severity from one person to another, including among members of the same family. cat eye syndrome may be best thought of as a disorder spectrum. While some people may have few or mild manifestations, others may have multiple severe malformations.
Table 1 gives the estimated incidence of symptoms from two different studies. These estimates are likely to be overestimates. Some affected individuals may manifest no symptoms (asymptomatic) or so few symptoms that they may not be diagnosed with the disorder. Although the cat eye syndrome chromosome is usually new and not inherited from a parent, there are a few inherited cases where the birth of a child with multiple features of cat eye syndrome results in the discovery of a mild case in a parent. The incidence of mild unrecognized cases of cat eye syndrome in the population, while likely rare, is unknown. The presence of the cat eye syndrome chromosome therefore in no way predicts the presence or severity of symptoms. Affected individuals will rarely have all of the symptoms discussed below and every case is different and unique. If a symptom is present in only one case, that may have an independent cause (not part of the syndrome). Parents should talk to their children’s physician and medical team about their child, potential associated symptoms and overall prognosis.
Table 1. Typical features of cat eye syndrome present in over 10% of affected individuals
| Symptom | Berends et al. 3 | Rosias et al. 4 |
| Coloboma (eye defect) | 55% (40/73) | 61% (54/88) |
| Downslanting palpebral fissures (eye abnormality) | 7% (34/73) | 69% (48/70) |
| Hypertelorism (wide set eyes) | 38% (28/73) | 70% (48/69) |
| Microphthalmia (small eye) | 19% (10/54) | 39% (23/59) |
| Epicanthal folds | 26% (19/74) | 64% (29/45) |
| Anal and rectum defects | 73% (54/74) | 81% (71/88) |
| Preauricular tags or pits (Outer ear defect) | 81% (60/74) | 87% (78/90) |
| Hearing loss | 17% (9/54) | 16% (11/68) |
| Heart defects | 50% (37/74) | 3% (50/80) |
| Kidney Defects | 31% (22/72) | |
| Kidney and Genital Defects | 71% (55/77) | |
| Intellectual disability | 32% (16/50) | 56% (38/68) |
| Skeletal defects | 29% (21/73) | 73% (46/63) |
| Abdominal defects | 69% (33/48) | |
| 12.5% (6/48) | |
| 8% (4/48) | |
| Cleft Palate | 14% (10/72) | |
| Cleft palate or absent uvula | 31% (15/48) | |
| Short stature | 15% (9/62) | 50% (32/64) |
Are there prenatal tests for cat eye syndrome?
Yes, 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 defects such as a heart defect that might suggest cat eye syndrome. During amniocentesis, a sample of amniotic fluid containing fetal cells is removed and analyzed, while CVS (chorionic villus sampling) involves the removal of tissue samples from a portion of the placenta. Chromosomal studies performed on such cells may reveal the cat eye syndrome chromosome.
What causes cat eye syndrome?
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 usually present in four copies (partial tetrasomy) rather than two copies in cells of the body. The diagnosis of cat eye syndrome is based on the presence of extra chromosomal material derived from chromosome 22, as described below.
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, plus two X chromosomes for females and an unequal 23rd pair of X and Y chromosomes for males. 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 have two 22nd chromosomes, both of which consist of a short arm (22p), a long arm (22q), and a centromere. However, almost all individuals with Cat eye syndrome have an unusual extra chromosome (supernumerary bisatellited marker chromosome). This marker chromosome is derived from two segments of chromosome 22, each of which consist of the short arm, the centromere and a piece of the long arm (22q11), both fused together to form a single extra chromosome. Therefore, this chromosomal region (22pter-22q11) is present in cells of the body four times: twice as part of the two normal chromosomes 22, and twice together in the marker chromosome. In addition, in some people, this extra chromosome may be present in only a certain percentage of the body’s cells (mosaicism). Mosaicism seen in the blood cells that are examined does not necessarily predict milder symptoms. There is no way to anticipate the specific symptoms or severity of an infant with a mosaic form of Cat eye syndrome.
In rare instances, a portion of the chromosomal segment 22 q11 may appear three times: once in a normal chromosome 22 and twice in a chromosome 22 with an internal duplication. A portion of region 22q11 is considered critical for expression of all or most of the features associated with Cat eye syndrome. This region is referred to as the Cat eye syndrome critical region and contains approximately 12 genes. Research is ongoing to isolate and characterize the gene(s) responsible for features associated with Cat eye syndrome.
How is cat eye syndrome inherited?
The exact cause of cat eye syndrome is not understood. In most instances, the chromosomal abnormality appears to arise “de novo” or random mutation due to an error in the division of a parent’s reproductive cells (meiotic error); in such cases, the parent has normal chromosomes. Formation of the marker chromosome may be a result of specific sequences in the region that predispose to chromosomal rearrangement. It not due to any specific actions taking by the parents during pregnancy.
In a small percentage of people, a parent (especially with milder symptoms) will pass the cat eye syndrome chromosome to their offspring. In some of these instances, the parent has the marker chromosome in some body cells while other body cells are unaffected (mosaicism). There have been instances reported where 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, those with multiple or severe features may be identified while previous generation go unrecognized and undiagnosed. In any case, it is important to note that individuals with Cat eye syndrome who have children run a substantial risk of passing the extra marker chromosome to a proportion of their offspring.
Further research is necessary to learn more about the complex chromosomal and genetic mechanisms potentially responsible for the expression and transmission of cat eye syndrome.
People with specific questions about genetic risks or genetic testing for themselves or family members should speak with a genetics professional.
Resources for locating a genetics professional in your community are available online:
- The National Society of Genetic Counselors (https://www.findageneticcounselor.com/) offers a searchable directory of genetic counselors in the United States and Canada. You can search by location, name, area of practice/specialization, and/or ZIP Code.
- The American Board of Genetic Counseling (https://www.abgc.net/about-genetic-counseling/find-a-certified-counselor/) provides a searchable directory of certified genetic counselors worldwide. You can search by practice area, name, organization, or location.
- The Canadian Association of Genetic Counselors (https://www.cagc-accg.ca/index.php?page=225) has a searchable directory of genetic counselors in Canada. You can search by name, distance from an address, province, or services.
- The American College of Medical Genetics and Genomics (http://www.acmg.net/ACMG/Genetic_Services_Directory_Search.aspx) has a searchable database of medical genetics clinic services in the United States.
Cat eye syndrome symptoms
The classic symptoms associated with cat eye syndrome are ocular coloboma, anal atresia and the minor ear defect preauricular skin tags or pits 5. However, the syndrome is extremely variable, and it has been estimated that only 41% of patients with cat eye syndrome have this classic triad of symptoms 3. In general the abnormalities associated with cat eye syndrome tend to involve the eyes, ears, anal region, heart, and/or kidneys, but other organs may show involvement and some people show intellectual disability.
Below are discussed the most common features of cat eye syndrome.
Coloboma and other eye abnormalities
A coloboma (plural colobomata or colobomas) consists of the partial absence of ocular tissue, often affecting both eyes (bilateral). It results from the failure to close a fissure in the lower part of the eye during early development, resulting in a cleft or gap that persists. Affected ocular tissues may include the colored portion of the eye that controls the amount of light that enters into the eye (iris), the dark-brown, middle layer (choroid), and/or the nerve-rich innermost membrane (retina) of the eye. Iris coloboma may give the iris an unusual “keyhole” appearance. If only the iris is involved, then vision is not affected. However, a more extensive coloboma involving other layers of the eye may result in vision defects and/or blindness. Although coloboma was originally considered a primary feature of the disorder, this abnormality is only present in a little over half of individuals with cat eye syndrome.
Some affected individuals have additional eye abnormalities, such crossing of the eyes (strabismus); and/or abnormal smallness of one of the eyes (unilateral microphthalmia). Less frequently, other ocular defects may be present including 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 the 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, including blindness.
Anal abnormalities
In approximately ¾ of affected individuals, the anal opening may be unusually small or narrow (anal stenosis) or the anal canal may be absent (anal atresia), sometimes 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. Anal atresia and fistulae are corrected surgically.
Ear Abnormalities
The third classic feature of cat eye syndrome is preauricular skin tags and/or pits. It is the most common feature of cat eye syndrome, seen in over 80% of people. Affected individuals may have small outgrowths of skin (tags) and/or slight depressions (pits) in front of the outer ears (preauricular). In addition, the outer portions of the ears (auricles) may be low set and/or malformed (dysplastic), sometimes 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).
Heart defects
About half of individuals with cat eye syndrome 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. In people with severe disease, congenital heart disease may lead to life-threatening complications.
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 total anomalous pulmonary venous return, 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. There is also a hole between the two atria (atrial septal defect), leading to mixing of oxygenated and oxygen-deficient blood. Associated symptoms and findings may include bluish discoloration of the skin and mucous membranes due to low blood oxygen (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. Although total anomalous pulmonary venous return is a rare heart defect, representing only 1-2% of heart defects in children, it is one of the most common heart defects in cat eye syndrome.
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. The symptoms associated tetralogy of Fallot can different in one person compared to another.
Holes between the atria or ventricles (atrial or ventricle septal defects) are also common heart defects associated with cat eye syndrome. A variety of other heart defects have been reported.
Kidney and genital defects
Collectively defects of the urinary system and the reproductive organs are classified as urogenital defects. These two systems have a common origin in the embryo. Typical kidney defects associated with cat eye syndrome include underdevelopment of one or both kidneys (unilateral or bilateral renal hypoplasia); absence of a kidney (unilateral 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). Typical reproductive tract defects in females include underdevelopment of the uterus, absence of the vagina or abnormal genitalia. In males defects include undescended testes (cryptorchidism) and external genital abnormalities.
Intellectual disability
Some individuals with cat eye syndrome have normal intelligence. However, some may have borderline normal to mild intellectual disability, or, less commonly, moderate intellectual disability. Berends et al, 2001 3 compared the IQ scores of 51 patients and found 47% in the normal range, 22 % borderline normal, 18% with mild intellectual disability and 14% with moderate intellectual disability. Rare cases of severe intellectual disability have also been reported. Individuals with intellectual disability may experience delays in reaching developmental milestones that require the coordination of muscular and mental activity (psychomotor delays).
Skeletal defects
Typical skeletal abnormalities 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.
Abdominal defects
In some individuals with cat eye 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). Additional reported features have included an abnormal saclike protrusion (Meckel diverticulum) from the lower small intestine (ileum), or Hirschsprung disease, which is the incomplete rotation of the upper large intestine (cecum), and/or the absence of groups of nerve fibers (ganglia) in the muscular wall of the large intestine 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.
In addition, 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. Without appropriate treatment, scarring and impaired functioning of the liver may lead to potentially life-threatening complications.
Cleft Palate
Cleft palate is the incomplete closure of the roof of the mouth. Varying degrees of this defect may be seen in 14-31% of individuals with cat eye syndrome 3.
Short Stature
Short stature has been reported in 15-50% of individuals with cat eye syndrome 3. However, it is not yet clear that this is associated with a deficiency of growth hormone in most affected individuals.
Abnormal facial features
Most individuals with cat eye syndrome show abnormal features of the skull and facial (craniofacial) region. Common features include downwardly slanting eyelid folds (palpebral fissures); eyes that are widely spaced apart (ocular hypertelorism), and vertical skin folds that may cover the inner corners of the eyes (epicanthal folds), an abnormally small lower jaw (mandibular hypoplasia or micrognathia) and a flat nasal bridge.
Cat eye syndrome diagnosis
The diagnosis of cat eye syndrome is based on the presence of extra chromosomal material derived from chromosome 22q11. 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 defects such as a heart defect that might suggest Cat eye syndrome. During amniocentesis, a sample of amniotic fluid containing fetal cells is removed and analyzed, while CVS involves the removal of tissue samples from a portion of the placenta. Chromosomal studies performed on such cells may reveal the cat eye syndrome chromosome.
Cat eye syndrome may be recognized after birth (postnatally) by a thorough clinical evaluation, detecting a subset of characteristic physical findings such as 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. A suspected diagnosis is then confirmed by standard chromosomal studies to identify the cat eye syndrome chromosome or a duplication within the 22q11 region.
Once a chromosomal diagnosis is made, various specialized tests may also be performed to determine whether other features of cat eye syndrome are present. In particular, 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 tests should include 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.
Specialized imaging techniques and/or other tests may also be used to detect and/or characterize possible gastrointestinal, genitourinary, renal, skeletal, or biliary defects, as well as other physical abnormalities that may occur in association with Cat eye syndrome. Investigation of cognitive function may also be appropriate.
Cat eye syndrome treatment
The treatment of cat eye syndrome may require the coordinated efforts of a team of medical professionals, such as pediatricians, surgeons, heart specialists (cardiologists), specialists 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 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, 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 affected individuals and their families. Chromosomal studies may be recommended for parents of affected individuals to determine whether they carry the cat eye syndrome chromosome or exhibit mosaicism for this chromosome, particularly if they manifest any features that may be associated with the disorder. Genetic counseling may also benefit adults with cat eye syndrome who are interested in having children.
Cat eye syndrome prognosis
Some patients die from severe malformations in early infancy. Otherwise, life expectancy is generally not significantly reduced.
References- Cat-eye syndrome. https://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=en&Expert=195
- Schinzel A., Schmid W., Auf der Maur P., et al. Incomplete trisomy 22. I. Familial 11/22 translocation with 3:1 meiotic disjunction. Delineation of a common clinical picture and report of nine new cases from six families. Human Genetics. 1981;56(3):249–262. doi: 10.1007/bf00274675
- Phenotypic variability of Cat-Eye syndrome. Berends MJ, Tan-Sindhunata G, Leegte B, van Essen AJ. Genet Couns. 2001;12(1):23-34. https://www.ncbi.nlm.nih.gov/pubmed/11332976
- Rosias PR, Sijstermans JM, Theunissen PM, et al., Phenotypic variability of the cat eye syndrome. Case report and review of the literature. Genet Couns. 2002;12:273-82.
- Cat eye syndrome. https://rarediseases.org/rare-diseases/cat-eye-syndrome/
