Cat Eye Syndrome (CES) is a rare chromosomal disorder presenting with a wide spectrum of physical and developmental traits. It is also known as Schmid-Fraccaro syndrome.
Defining the Genetic Cause
The cause of Cat Eye Syndrome lies in an abnormality of chromosome 22, specifically involving a duplicated segment on the long arm designated 22q11. This duplication typically results in a partial tetrasomy, meaning four copies of this segment are present instead of the usual two. This extra segment often forms a small, supernumerary marker chromosome (sSMC).
The presence of this extra chromosome causes a gene dosage imbalance, disrupting normal development across multiple organ systems. Most cases arise spontaneously (de novo) during the formation of the egg or sperm cell. In a minority of instances, the condition can be inherited from a parent who carries the sSMC. The severity of the syndrome does not always correlate directly with the size of the duplicated segment.
Prevalence and Incidence Statistics
Cat Eye Syndrome is a rare disease with variable reported figures. Estimated incidence rates range widely, typically cited between 1 in 50,000 and 1 in 150,000 live births. The disorder appears to affect males and females with equal frequency.
Determining the exact prevalence is challenging because many individuals with very mild forms of CES may go undiagnosed. Milder cases present with only a few subtle anomalies, making clinical recognition difficult without genetic testing. This variability in presentation suggests that the true prevalence figures are likely higher than current estimates.
Distinctive Physical Features
Cat Eye Syndrome is characterized by a set of physical features, though no single feature is present in every affected individual. The syndrome gets its name from the ocular coloboma, a defect in the eye structure, often in the iris, which can make the pupil appear elongated like a cat’s vertical slit. Coloboma is present in about half of patients and can affect the retina or choroid as well as the iris.
Anomalies of the ear are considered the most consistent feature, occurring in a large percentage of individuals. These commonly include small skin tags or pits located just in front of the ear, known as preauricular tags or pits. Another characteristic finding is anal atresia, which is an abnormal or absent opening of the anus, often requiring surgical correction shortly after birth.
The syndrome frequently involves congenital malformations affecting internal organs. Approximately half of those affected have structural heart defects, which can range from minor issues to severe conditions like Total Anomalous Pulmonary Venous Return (TAPVR). Kidney abnormalities are also common, including the absence of a kidney (renal agenesis) or underdeveloped kidneys (hypoplasia). Although intellectual development is often normal or only mildly impaired, some individuals may experience moderate learning difficulties.
Clinical Diagnosis and Ongoing Management
Initial suspicion of Cat Eye Syndrome is raised by observing characteristic physical features in a newborn or infant. Confirmation requires genetic testing to visualize the extra chromosomal material. Standard karyotyping can reveal the presence of the small supernumerary marker chromosome derived from chromosome 22.
More advanced techniques, such as Fluorescence In Situ Hybridization (FISH) or array Comparative Genomic Hybridization (aCGH), are used to confirm the duplication of the 22q11 region. These high-resolution methods are particularly important for detecting low-level mosaicism, where the extra chromosome is present in only some of the body’s cells.
Management for CES is supportive and highly individualized due to the wide variability in symptoms. A multidisciplinary team of specialists, including cardiologists, ophthalmologists, and urologists, addresses specific organ defects. Surgical interventions are frequently necessary for congenital heart defects and anal atresia. Early intervention programs, physical therapy, and educational support are utilized to manage developmental and learning differences.