Does Cat Eye Syndrome Run in Families? Unraveling the Genetics Behind This Rare Disorder

Introduction to Cat Eye Syndrome

Cat eye syndrome (CES) is a rare congenital chromosomal disorder characterized by an extra (partial or complete) duplicate of genetic material from chromosome 22 being present in a person’s cells. This extra genetic material causes a range of symptoms and physical features that can vary greatly in range and severity between affected individuals. Some common features include distinctive eye abnormalities, such as pupils that resemble the eyes of a cat, as well as heart defects, kidney problems, and intellectual disability or learning difficulties.

The prevalence of cat eye syndrome is estimated at 1 in 50,000 to 1 in 150,000 births. The syndrome affects males and females in equal numbers and has been identified in all ethnic groups. However, the syndrome is likely underdiagnosed due to variation in symptoms and lack of awareness among health care providers.

Genetics and Inheritance

Cat eye syndrome is caused by a partial tetrasomy of chromosome 22, meaning there is an extra copy of part of this chromosome in each cell. This extra genetic material almost always occurs randomly when the sperm or egg cell is forming, rather than being inherited from a parent. Only about 1% of cat eye syndrome cases are inherited from a parent with a rearranged chromosome 22.

The extra partial copy of chromosome 22 most often includes the q11.1 and q11.2 regions. Having this extra genetic material disrupts the normal development of many parts of the body, leading to the signs and symptoms of cat eye syndrome.

Cat eye syndrome is considered a sporadic genetic disorder, since it arises randomly and is not usually passed down through families. However, someone who carries a chromosomal rearrangement involving chromosome 22 has an increased risk of passing the abnormality to their children. In those rare inherited cases, cat eye syndrome can have an autosomal dominant pattern of inheritance.

Prenatal testing, such as amniocentesis or chorionic villus sampling, can detect cat eye syndrome during pregnancy. Genetic counseling can help parents understand their chances of having a child with cat eye syndrome.

Physical Characteristics

Some of the most common physical characteristics of cat eye syndrome include:

child with cat eye syndrome characteristics

  • Coloboma of the iris – This is a gap or cleft in the iris of the eye below the pupil, which makes the pupil look elongated like a cat’s eye. It occurs in over 90% of people with cat eye syndrome.1
  • Preauricular pits – These are small holes or dimples in front of the ears. They occur in over 70% of people with cat eye syndrome.2
  • Downslanted palpebral fissures – This refers to eyes that slant downwards at the outer corners. It is present in about 65% of people with cat eye syndrome.

Other common physical features include low-set and malformed ears, heart defects, kidney problems, and developmental delays. The severity of symptoms can vary greatly among individuals with cat eye syndrome.

Developmental Effects

Cat eye syndrome often causes intellectual disability and delayed development. According to the National Organization for Rare Disorders (NORD), intellectual disability occurs in 50-60% of people with cat eye syndrome. The intellectual disability can range from mild to severe. Language and speech delays are also common, with some individuals being unable to speak. Motor skills like sitting, standing and walking may be delayed as well.

child receiving speech therapy

A study published in Molecular Cytogenetics found that 100% of participants with cat eye syndrome had developmental delay and 90% had speech delay (Tao et al., 2013). The study also found that the severity of intellectual disability correlated with the size of the genetic deletion on chromosome 22.

Early intervention with speech therapy, physical therapy and special education services can help children with cat eye syndrome reach their full potential. However, intellectual disability and developmental delays remain very common features of this condition.

Other Health Conditions

Cat eye syndrome is often associated with congenital heart defects, which occur in 50-60% of cases according to the National Organization for Rare Disorders (https://rarediseases.org/rare-diseases/cat-eye-syndrome/). The most common heart defects include atrial septal defect, ventricular septal defect, tetralogy of Fallot, and patent ductus arteriosus. Kidney malformations are also common, occurring in 30-50% of individuals with cat eye syndrome. These malformations can lead to loss of kidney function. Another condition associated with cat eye syndrome is anal atresia, which is the absence of an opening for the anus. This occurs in 10-25% of cases. Cleft palate is also sometimes present.

Diagnosis

Cat eye syndrome is usually diagnosed through a chromosome analysis called a karyotype. This test analyzes the number and appearance of chromosomes in a sample of blood, skin, or other tissue.

People with cat eye syndrome have an extra (partial trisomy) chromosome 22 in some or all of their cells. The extra genetic material disrupts normal development, causing the signs and symptoms of this disorder.

Specifically, a karyotype analysis will show that affected individuals have an abnormally shaped chromosome 22, resulting from the duplication of the top portion of chromosome 22. This duplicated section of chromosome 22 is attached to the bottom of another chromosome 22, forming a dicentric chromosome that resembles the shape of a cat’s eye, hence the disorder’s name.

Detecting the characteristic karyotype confirms the diagnosis of cat eye syndrome.

Source: https://rarediseases.org/rare-diseases/cat-eye-syndrome/

Treatment

There is currently no cure for cat eye syndrome as it is caused by a permanent change to a chromosome. However, many of the symptoms can be treated and managed (https://www.webmd.com/parenting/baby/cat-eye-syndrome-facts). The treatment focuses on addressing the specific symptoms present in each individual and providing support.

child meeting with medical team

Treatment may involve a team of specialists including pediatricians, surgeons, cardiologists, ophthalmologists, audiologists and physical/occupational therapists. Surgery may be needed to correct heart defects, cleft palate and other physical abnormalities. Medications can help manage immune deficiencies, respiratory infections, and other health conditions. Hearing aids and speech therapy may help with hearing loss. Eyeglasses can correct vision issues. Physical/occupational therapy can improve motor skills. Early intervention services are important for optimizing development.

Providing social and emotional support to children and families living with cat eye syndrome is also an important part of management. Connecting with support groups and finding community resources can help families cope. While there is no cure, treatment focusing on symptomatic management and support can significantly improve quality of life.

Prognosis

The prognosis for individuals with cat eye syndrome can vary greatly depending on the severity of symptoms. However, most people with the condition have a normal life expectancy (1). While some severely affected infants unfortunately may die during infancy, the majority of people with cat eye syndrome do not have a shortened lifespan (2).

The severity of symptoms is highly variable between individuals with cat eye syndrome. Some may have only mild symptoms like eyes that are spaced wider apart, while others can have more complex medical problems affecting the heart, kidneys, and other organs. Even within the same family, the effects can range from relatively mild to quite severe (3).

With appropriate treatment and management of any medical issues present, many individuals with cat eye syndrome can have a good quality of life. However, the variability in symptoms makes it difficult to generalize the prognosis. Lifespan is usually normal, but severity of symptoms varies widely between affected individuals.

Sources:
(1) https://www.news-medical.net/health/What-is-Cat-Eye-Syndrome.aspx
(2) https://www.healthline.com/health/cat-eye-syndrome
(3) https://rarediseases.org/rare-diseases/cat-eye-syndrome/

Causes

Cat eye syndrome is caused by an extra (supernumerary) chromosome 22 in the cells of the body. Specifically, it is caused by an extra duplicated region of the chromosome called 22pter->22q11. Most people have two copies of chromosome 22 in each cell. But people with cat eye syndrome have three copies of this region of chromosome 22 in some or all of their cells.

This extra genetic material disrupts normal development, causing the signs and symptoms of cat eye syndrome. The extra chromosome is the result of a random error that occurs when egg or sperm cells are forming or within the first few cell divisions after fertilization. As a result, cat eye syndrome is considered a sporadic genetic change with a low recurrence risk (Source).

In a very small number of cases, one parent is a carrier of a rearrangement of genetic material between chromosome 22 and another chromosome. This can increase the risk of having a child with cat eye syndrome. Advanced parental age may also increase the risk of chromosome abnormalities, but there is insufficient evidence showing a direct link between parental age and cat eye syndrome (Source).

Support and Coping

support group meeting
Early diagnosis and intervention services are key for children with cat eye syndrome. Services like occupational, physical, and speech therapy can help address developmental delays and other issues caused by the disorder. Parents should consult with their child’s doctor to determine which therapies would be most beneficial.

Connecting with support groups can also provide important resources for families coping with cat eye syndrome. Organizations like Cat Eye Syndrome International (CESI) provide information on what to expect when dealing with the disease. They can connect families to medical professionals familiar with treating cat eye syndrome and to other families going through similar experiences. Support groups help parents and caregivers feel less alone in managing their child’s care.

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