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PubMed This is a summary of 9 peer-reviewed journal articles Updated
Genetics

Navigating the Diagnostic Pathway

At a Glance

Cat-Eye Syndrome is diagnosed using three main genetic tests: a karyotype to spot an extra marker chromosome, FISH to confirm the material is from chromosome 22, and a microarray to map its exact size. The percentage of affected cells in mosaic cases does not predict symptom severity.

Navigating the world of genetic testing can feel like reading a complex blueprint. To confirm a diagnosis of Cat-Eye Syndrome (CES), doctors use a series of tests that look at your child’s chromosomes at different levels of detail.

Step 1: The Bird’s-Eye View (Karyotype)

The first test performed is usually a G-banding karyotype. This involves taking a picture of all the chromosomes in a cell and lining them up in pairs [1].

  • What it looks for: An extra, tiny chromosome that shouldn’t be there.
  • What you might see on the report: If a marker is found, the report may say 47,XX,+mar (for a girl) or 47,XY,+mar (for a boy). The “47” means there are 47 chromosomes instead of the usual 46, and “+mar” stands for the extra marker chromosome [2].
  • The limitation: A karyotype can see that an extra piece exists, but it is often too small to tell which chromosome it came from [3][1].

Step 2: The “Glow” Test (FISH)

To confirm the extra piece is actually from chromosome 22, doctors use Fluorescence In Situ Hybridization (FISH) [4].

  • How it works: Scientists use fluorescent “probes” that only stick to specific parts of chromosome 22. If the probes light up on the extra marker chromosome, it confirms the diagnosis of CES [2].

Step 3: The High-Resolution Map (CMA)

The “gold standard” for understanding the exact size of the extra piece is Chromosomal Microarray Analysis (CMA), sometimes called array-CGH [5][6].

  • What it does: This test looks at the genetic code in much higher resolution than a karyotype, determining the exact “breakpoints”—the start and end points of the extra material [5].
  • What you might see on the report: Look for coordinates like 22q11.1-q11.21. This indicates the specific neighborhood on chromosome 22 that has been duplicated [7][8].

Understanding Mosaicism on a Report

In about 40% of cases, CES is mosaic, meaning the extra marker is in some cells but not others [7].

On a lab report, mosaicism is often written with a forward slash separating two different cell counts. For example: 47,XX,+mar[15]/46,XX[35] [1].

  • The first part ([15]) shows how many cells had the extra marker.
  • The second part ([35]) shows how many cells were typical.
    In this example, 15 out of 50 cells (or 30%) carried the marker. While you might assume a lower percentage means milder symptoms, research shows that genotype-phenotype correlation in CES is poor [8]. The percentage of mosaic cells found in the blood test does not reliably predict how severe the clinical symptoms will be [7].

What to Look for in the Final Report

To ensure your child’s diagnosis is complete, check the “Interpretation” or “Results” section for these key terms:

  1. Supernumerary Marker Chromosome (sSMC): Confirms an extra piece was found [1].
  2. Partial Tetrasomy or Trisomy 22: Confirms the extra material is from chromosome 22 [7].
  3. idic(22)(q11.2): This notation describes an inverted duplication, the most common cause of CES [9][5].

Common questions in this guide

How is Cat-Eye Syndrome diagnosed?
Cat-Eye Syndrome is diagnosed through a combination of three genetic tests. A karyotype first spots an extra marker chromosome, FISH confirms the material is from chromosome 22, and a chromosomal microarray measures the exact size of the extra genetic piece.
What does '+mar' mean on my child's karyotype report?
The notation '+mar' indicates a supernumerary marker chromosome. This means the lab found an extra, tiny piece of genetic material that requires further specialized testing, like FISH, to identify where it came from.
Does the percentage of mosaicism predict how severe Cat-Eye Syndrome will be?
No, the percentage of mosaic cells found in a blood test does not reliably predict how severe the clinical symptoms will be. Research shows that the correlation between these genetic percentages and physical symptoms is poor.
What does idic(22)(q11.2) mean on a lab report?
This notation describes an inverted duplication of a specific section of chromosome 22. It confirms the exact location of the extra genetic material and is the most common cause of Cat-Eye Syndrome.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Can you walk me through each line of my child's genetic report and explain what it means for their specific diagnosis?
  2. 2.Since the karyotype showed an 'extra marker,' did the FISH or CMA testing confirm exactly that it came from chromosome 22?
  3. 3.Does my child have mosaicism, and if so, what percentage of their cells were found to carry the extra marker?
  4. 4.What are the specific 'breakpoints' or coordinates of the extra genetic material on chromosome 22?

Questions For You

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References

References (9)
  1. 1

    Prenatal diagnosis and molecular cytogenetic identification of small supernumerary marker chromosomes: analysis of three prenatal cases using chromosome microarray analysis.

    Xue H, Chen X, Lin M, et al.

    Aging 2020; (13(2)):2135-2148 doi:10.18632/aging.202220.

    PMID: 33318309
  2. 2

    [Prenatal diagnosis and clinical analysis of two fetuses with Cat-eye syndrome].

    Wu X, An G, He D, et al.

    Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics 2019; (36(5)):498-501 doi:10.3760/cma.j.issn.1003-9406.2019.05.021.

    PMID: 31030443
  3. 3

    Small supernumerary marker chromosomes and their correlation with specific syndromes.

    Jafari-Ghahfarokhi H, Moradi-Chaleshtori M, Liehr T, et al.

    Advanced biomedical research 2015; (4()):140 doi:10.4103/2277-9175.161542.

    PMID: 26322288
  4. 4

    Mosaic cat eye syndrome in a child with unilateral iris coloboma.

    Hernández-Medrano C, Hidalgo-Bravo A, Villanueva-Mendoza C, et al.

    Ophthalmic genetics 2021; (42(1)):84-87 doi:10.1080/13816810.2020.1839918.

    PMID: 33465332
  5. 5

    Congenital hypopituitarism and multiple midline defects in a newborn with non-familial Cat Eye syndrome.

    Serra G, Giambrone C, Antona V, et al.

    Italian journal of pediatrics 2022; (48(1)):170 doi:10.1186/s13052-022-01365-9.

    PMID: 36076277
  6. 6

    Cat eye syndrome caused by 22q11.1q11.21 duplication: case report in a Chinese family.

    Wang Y, Zhang P, Chai Y, Zang W

    Molecular cytogenetics 2023; (16(1)):28 doi:10.1186/s13039-023-00660-2.

    PMID: 37880750
  7. 7

    Cat eye syndrome: Clinical, cytogenetics and familial findings in a large cohort of 43 patients highlighting the importance of congenital heart disease and inherited cases.

    Jedraszak G, Jobic F, Receveur A, et al.

    American journal of medical genetics. Part A 2024; (194(4)):e63476 doi:10.1002/ajmg.a.63476.

    PMID: 37974505
  8. 8

    Clinical and molecular cytogenetic findings of cat eye syndrome and a 2-year-old patient with congenital aural atresia and hearing loss.

    Xu L, Cheng X, Tang L, et al.

    BMC pediatrics 2024; (24(1)):658 doi:10.1186/s12887-024-05136-9.

    PMID: 39402511
  9. 9

    A child with cat-eye syndrome and oculo-auriculo-vertebral spectrum phenotype: A discussion around molecular cytogenetic findings.

    Glaeser AB, Diniz BL, Santos AS, et al.

    European journal of medical genetics 2021; (64(11)):104319 doi:10.1016/j.ejmg.2021.104319.

    PMID: 34474176

This guide to interpreting genetic reports is for informational purposes only and does not replace professional medical advice. Always review test results with your child's geneticist or pediatrician.

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