Is Cat Eye Syndrome in Your Genes? Dominant vs Recessive Inheritance of this Rare Disorder

Introduction to Cat Eye Syndrome

Cat eye syndrome (CES) is a rare chromosomal disorder characterized by an extra chromosome 22 in some or all cells of the body (1). The most common features of CES include unusual eye findings like coloboma, anal atresia, heart defects, kidney problems, and mild to moderate intellectual disability (2, 3). The signs and symptoms of CES can vary widely, even among affected members of the same family (3).

The prognosis for individuals with CES depends on the symptoms present. Many of the structural defects can be corrected with surgery. However, intellectual disability may range from mild learning disabilities to more severe cognitive and developmental delays. Supportive therapy, special education, and vocational training can help improve development and quality of life. The life expectancy for individuals with CES is usually normal, unless complex congenital heart defects are present (1, 3).

Genetics and Inheritance

Cat eye syndrome is caused by a chromosomal abnormality. Specifically, it is caused by the presence of an extra (supernumerary) bisatellited marker chromosome derived from human chromosome 22. This extra genetic material leads to partial trisomy of chromosome 22. The extra chromosome is present in some cells but not others, leading to a chromosomal mosaicism.

Cat eye syndrome is considered a sporadic genetic disorder, meaning it usually occurs randomly due to a new mutation rather than being inherited from a parent. However, in about 10-15% of cases, the condition is inherited from a parent with mosaicism for the marker chromosome 22. When cat eye syndrome is inherited, it does not follow typical patterns of dominant or recessive inheritance. The amount of extra chromosome 22 material present in parental cells can influence recurrence risks for future children.

Overall, cat eye syndrome is a rare disorder, estimated to occur in 1 in 50,000 to 150,000 births. Both males and females are affected equally. The risk of recurrence depends on whether the parents are found to have mosaicism for the marker chromosome. For most families with an affected child, the recurrence risk is low at less than 1%. However, the risk may be as high as 50% if mosaicism is detected in a parent.

Sources:

[1] https://rarediseases.org/rare-diseases/cat-eye-syndrome/

[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC311098/

Chromosomal Abnormality

Cat eye syndrome is caused by a rare chromosomal abnormality characterized by the presence of an extra bisatellited marker chromosome, consisting of inverted duplicated material from chromosome 22q11 (https://rarediseases.org/rare-diseases/cat-eye-syndrome/). This extra genetic material leads to a partial trisomy for a small region of chromosome 22. In about 80% of cases, the marker chromosome is a small metacentric or submetacentric supernumerary chromosome, representing an inverted duplication of proximal 22q (https://rarediseases.info.nih.gov/diseases/26/cat-eye-syndrome).

illustration of chromosome abnormality

The most common karyotype seen in cat eye syndrome is 47,XX,+mar or 47,XY,+mar, indicating the presence of the extra marker chromosome. The marker is made up of two copies of the proximal long arm and centromere of chromosome 22, arranged in an inverted duplicated orientation. This abnormal chromosome contains two copies of genes from 22q11.1 to 22q11.21 (https://www.news-medical.net/health/What-is-Cat-Eye-Syndrome.aspx).

Prevalence

Cat eye syndrome is a rare chromosomal disorder that affects approximately 1 in every 50,000 to 150,000 births worldwide (WebMD). Some studies estimate the incidence to be around 1 in 65,000 live births (Gaspar & Vieira). The syndrome seems to occur randomly and has been reported in all ethnic groups. However, some research indicates it may be more common in populations where consanguineous marriages are prevalent (NORD).

Signs and Symptoms

Cat eye syndrome is characterized by a wide range of physical abnormalities and health conditions. Some of the most common signs and symptoms associated with cat eye syndrome include:

  • Facial abnormalities such as a cleft lip and/or palate, downward slanting eyelid folds, widely spaced eyes (hypertelorism), and flattened nose bridge
  • Ocular abnormalities including coloboma (a gap or split in the iris), microphthalmia (abnormally small eyes), strabismus (misaligned eyes), and nystagmus (involuntary eye movements)
  • Kidney abnormalities such as missing kidney, horseshoe kidney, or small dysplastic kidneys
  • Congenital heart defects like atrial septal defect, ventricular septal defect, Tetralogy of Fallot, or patent ductus arteriosus
  • Gastrointestinal malformations including imperforate anus, tracheoesophageal fistula, or annular pancreas
  • Skeletal abnormalities like extra, fused, or misshapen vertebrae
  • Hearing loss or deafness
  • Intellectual disability, learning disabilities, developmental delay
  • Growth deficiency – short stature

The severity and combination of abnormalities can vary widely between individuals with cat eye syndrome. Mild cases may involve only minor ocular defects and learning difficulties, while more severe cases present with multiple malformations and serious medical complications (NIH Rare Diseases). Early diagnosis and ongoing management by a team of specialists is important for the best possible outcomes.

child receiving developmental assessment

Developmental Issues

Children with cat eye syndrome often experience intellectual disability and developmental delays. These issues can range from mild to severe. Intellectual disability is present in 50-70% of individuals with cat eye syndrome and is often characterized by an IQ below 70. The degree of disability can vary widely. Some children may be able to live independently as adults while others require more support.

In addition to intellectual disabilities, children with cat eye syndrome frequently experience delays in reaching developmental milestones for motor skills, speech and language. They may be late in learning to walk, talk and care for themselves. Language deficits include delayed speech, poor pronunciation, and difficulties with grammar and expressing more complex ideas.

Learning disabilities are also common among those with cat eye syndrome. Challenges with reading, writing and mathematics are typical. Children may require special education services and other therapies to address their unique learning needs. Academic skills often continue to be an area of difficulty throughout their education.

Early intervention with speech therapy, physical therapy, occupational therapy and special education can help children reach their full potential. Ongoing support and accommodations continue to be important as they grow and learn new skills. While developmental delays may persist to adulthood, many people with cat eye syndrome are able to have meaningful relationships, find employment and enjoy an enhanced quality of life.

Sources:
https://rarediseases.org/rare-diseases/cat-eye-syndrome/
https://www.news-medical.net/health/What-is-Cat-Eye-Syndrome.aspx

Diagnosis

Cat eye syndrome is typically diagnosed through genetic testing. The main diagnostic test is a chromosome analysis called a karyotype, which allows doctors to examine the chromosomes for abnormalities. This test can identify the extra genetic material from chromosome 22 that causes cat eye syndrome.

Prenatal testing can also diagnose cat eye syndrome before birth. Tests like amniocentesis, chorionic villus sampling (CVS), or percutaneous umbilical blood sampling (PUBS) allow doctors to analyze the fetus’s chromosomes for abnormalities. Ultrasound may also detect some physical signs of cat eye syndrome prenatally, like heart defects or kidney issues, prompting further genetic testing.

If cat eye syndrome is suspected after birth, doctors will examine the infant for characteristic signs like eye abnormalities (coloboma, microphthalmia), heart defects, kidney problems, and anal atresia. These distinctive features, along with delayed development, may indicate the need for chromosome analysis to confirm the diagnosis.

Early diagnosis through genetic testing allows parents and doctors to plan for treatments and interventions to manage symptoms and developmental issues associated with cat eye syndrome.

Treatment and Management

child wearing cochlear implant hearing aids
There is currently no cure for cat eye syndrome since it is caused by a chromosomal abnormality. However, treatment aims to manage the various symptoms associated with the condition. This often involves a coordinated team of healthcare professionals such as pediatricians, cardiologists, ophthalmologists, audiologists and physical/occupational therapists.

Some of the key areas of treatment and management include:

  • Medical care – Managing heart defects with surgery or medication, monitoring for recurrent infections, treating refractive errors with glasses or contact lenses, managing hearing loss with hearing aids or cochlear implants.
  • Therapies – Physical, occupational and speech therapy to help with delayed development and motor skills issues. Cognitive behavioral therapy may help with social and behavioral problems.
  • Educational support – An individualized education plan (IEP) to provide accommodations and interventions tailored to the child’s needs and abilities. This may involve special education services, assistive technology, small classroom sizes etc.

Lifelong and proactive medical care is crucial for preventing complications and maintaining quality of life. Providing educational support and early intervention services can help children with cat eye syndrome reach their full potential. While there is no cure, appropriate treatment and management can significantly improve outcomes.

Prognosis

The prognosis for individuals with cat eye syndrome varies greatly depending on the severity of symptoms and associated complications. While some people with mild cases may live a relatively normal life, others with more significant issues may have reduced life expectancy and ongoing disabilities.

group of children with disabilities smiling

One study found that around 70% of people with cat eye syndrome had a normal life expectancy, while 30% had reduced lifespan, often related to congenital heart defects or kidney malformations (Source 1). However, with advances in medical care and treatment options, life expectancy is improving overall.

Many of the congenital defects associated with cat eye syndrome can be corrected with surgery early in life. However, developmental delays and intellectual disability may persist and require ongoing special education and support services. Adults may need assisted living arrangements depending on their level of functioning.

Regular follow-up with a multidisciplinary team is important for optimal outcomes. This allows early intervention for any emerging issues. With appropriate management and support, many individuals with cat eye syndrome can live fulfilling lives within their capabilities.

Resources

There are several organizations that provide support and resources for individuals and families affected by Cat Eye Syndrome.

Cat Eye Syndrome International (CESI) is a non-profit organization dedicated to improving the lives of those with Cat Eye Syndrome through education, support, and research. CESI provides an online community, conferences, a newsletter, and information on medical issues related to the syndrome. Learn more at their website: https://rarediseases.org/organizations/cat-eye-syndrome-international/

The National Organization for Rare Disorders (NORD) also has an informational page on Cat Eye Syndrome which provides an overview of causes, symptoms, diagnosis, and management of the condition. More details can be found on their website: https://rarediseases.info.nih.gov/diseases/26/cat-eye-syndrome

In addition to these organizations, connecting with other families and joining Cat Eye Syndrome support groups can provide solidarity and allow families to share experiences and advice. Numerous online groups and in-person meetings are available.

Further reading on recent research and clinical management of Cat Eye Syndrome can be found in medical journals and publications. Consulting with a genetic counselor or medical genetics specialist is also recommended for the most up-to-date information and care recommendations.

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