Cat Eye Syndrome (CES) is a rare genetic condition with specific physical features, present from birth and affecting different body systems. Understanding CES involves recognizing its unique manifestations and underlying genetic changes.
The Chromosomal Anomaly
Cat Eye Syndrome results from an extra, abnormal chromosome. This supernumerary chromosome is derived from chromosome 22, containing duplicated or triplicated genetic material. The specific region involved is the long arm of chromosome 22, at band 22q11.2. This means that individuals with CES possess three or four copies of genes normally present in two copies, located within this particular segment of chromosome 22.
This additional genetic material leads to an excess of gene products. This gene dosage imbalance disrupts normal developmental processes. The precise genes within the 22q11.2 region that contribute to each specific feature of the syndrome are still under investigation, but their overexpression is understood to be the direct cause of the diverse clinical manifestations observed in affected individuals.
How the Anomaly Arises
Most cases of Cat Eye Syndrome arise “de novo,” meaning the chromosomal anomaly is a new occurrence and is not inherited. This typically results from an error during the formation of reproductive cells, either eggs or sperm. These errors often involve non-disjunction, where chromosomes fail to separate properly during meiosis, the cell division that creates gametes.
An abnormal recombination event during meiosis can also lead to this extra chromosome, resulting in an unbalanced rearrangement of genetic material. In rare instances, Cat Eye Syndrome can be inherited from a parent who carries a balanced chromosomal rearrangement, such as a translocation or inversion, involving chromosome 22. Such a parent may not show symptoms of the syndrome but can pass on an unbalanced form to their offspring.
Recognizing Cat Eye Syndrome
The syndrome is named for a distinctive ocular feature: coloboma of the iris. This appears as a gap or hole in the colored part of the eye, resembling a cat’s pupil.
Many individuals also present with preauricular tags or pits, which are small skin growths or depressions located in front of the ears. Another common characteristic involves anal anomalies, frequently an imperforate anus, where the anal opening is absent or improperly formed.
Other potential features include various heart defects, with total anomalous pulmonary venous return being a less common but reported finding. Kidney abnormalities, such as underdeveloped or absent kidneys, can also occur. The degree of intellectual disability in individuals with Cat Eye Syndrome varies significantly, ranging from normal intelligence to severe impairment. These diverse physical signs are all expressions of the underlying genetic imbalance.
Diagnosis and Genetic Counseling
Diagnosis of Cat Eye Syndrome is confirmed through specific genetic testing methods. Karyotyping, which involves examining a person’s chromosomes, can often identify the extra, abnormal chromosome 22. Fluorescence In Situ Hybridization (FISH) is another technique that uses fluorescent probes to detect the duplicated region on chromosome 22q11.2 with higher precision. Chromosomal microarray (CMA) offers a more detailed analysis, capable of identifying smaller duplications or triplications of genetic material on chromosome 22.
Genetic counseling plays a significant role for families affected by Cat Eye Syndrome. Counselors help families understand the diagnosis, including the specific genetic changes involved and their implications for the individual’s health. They also discuss the typically low recurrence risk for future pregnancies in de novo cases, providing information on the probability of having another child with the syndrome. This guidance assists families in making informed decisions regarding family planning and medical management.