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PubMed This is a summary of 22 peer-reviewed journal articles Updated
Medical Genetics

Biology, Testing, and Genetic Reports

At a Glance

Diagnosing Ring Chromosome 13 Syndrome requires multiple tests. A karyotype identifies the physical ring shape and mosaicism, while a microarray pinpoints exact missing genes like RB1 or CHAMP1. Because the ring is unstable, symptoms vary widely depending on dynamic mosaicism.

Understanding your child’s genetic report is a critical step in navigating Ring Chromosome 13 Syndrome. Because this condition is so complex, doctors use several different types of tests to build a complete picture of what is happening in your child’s cells.

Testing: Seeing the Big and Small Pictures

No single test tells the whole story. Instead, doctors combine different technologies to understand both the structure and the instructions of the chromosomes [1][2].

The Karyotype: Looking at Structure

A karyotype is like taking a photograph of all the chromosomes under a microscope [1].

  • What it sees: It can physically see the ring shape of chromosome 13 [1][3].
  • Mosaicism: It is the best tool for seeing mosaicism—the percentage of cells that have the ring versus cells that have lost it entirely [4][5].

Chromosomal Microarray (CMA): Looking at Instructions

A microarray is a molecular test that scans the chromosome for missing or extra pieces of DNA [2].

  • Breakpoints: It identifies exactly where the chromosome broke (the “breakpoints”) and which specific genes are missing [2][6].
  • Limitation: It cannot “see” the ring shape itself or tell you if the chromosome is circular [1].

Long-Read Sequencing: The High-Definition View

This newer technology provides the highest resolution possible, mapping the exact sequence of DNA across the breakpoints to reveal complex rearrangements that other tests might miss [7][8].

Why Prognosis is Challenging: Dynamic Mosaicism

One of the most confusing parts of this diagnosis is that the ring chromosome is unstable [5]. When cells divide, the ring can become tangled, break, or fail to move into the new cell [9][4].

This leads to dynamic mosaicism, where different tissues in your child’s body (like the brain, blood, or skin) may have different percentages of:

  1. Ring Cells: Cells with the original ring.
  2. Monosomy Cells: Cells missing one copy of chromosome 13 entirely [4][5].
  3. Rearranged Cells: Cells with complex, secondary changes to the ring [5].

Because we cannot easily test every tissue, it is difficult for doctors to predict exactly how the syndrome will progress [10][11].

Mapping the Critical Genes

The symptoms your child experiences are largely driven by the loss of specific genes within the deleted sections of chromosome 13 [12].

Gene Location Associated Features
RB1 13q14.2 Significant risk for retinoblastoma (eye cancer); often requires frequent exams [13][14].
ZIC2 13q32.3 Associated with holoprosencephaly (brain midline differences) and microcephaly [15][16].
EFNB2 13q33.3 Involved in the development of the heart and urogenital systems [17][18].
CHAMP1 13q34 Linked to intellectual disability, low muscle tone (hypotonia), and severe speech delays [19][20].

By identifying which of these genes are missing on your child’s microarray report, your medical team can prioritize the most important screenings and therapies [21][22].

Common questions in this guide

What is the difference between a karyotype and a microarray for Ring Chromosome 13?
A karyotype looks at the physical structure of the chromosomes under a microscope to see the ring shape and check for mosaicism. A microarray scans the chromosome at a molecular level to identify the exact breakpoints and which specific genes are missing.
What does dynamic mosaicism mean in Ring Chromosome 13 Syndrome?
Because the ring chromosome is unstable, it can break or fail to divide properly. This creates dynamic mosaicism, meaning different tissues in your child's body may have varying percentages of cells with the ring, cells missing the chromosome entirely, or cells with secondary changes.
Why is the RB1 gene important on my child's microarray report?
The RB1 gene is located on chromosome 13 and acts to prevent tumors. If this gene is included in the deleted section of your child's chromosome, they have a significantly higher risk of developing an eye cancer called retinoblastoma and will need frequent specialist eye exams.
Which missing genes cause developmental delays in Ring Chromosome 13?
The loss of specific genes drives many developmental symptoms. For example, the missing CHAMP1 gene is strongly linked to intellectual disability, low muscle tone, and severe speech delays, while the missing ZIC2 gene is associated with structural brain differences.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Can you walk me through the specific 'breakpoints' on my child's 13q arm and which genes listed in this guide are missing?
  2. 2.My child's karyotype shows a certain percentage of ring cells. How does this level of mosaicism compare to what you typically see?
  3. 3.Is the RB1 gene (13q14.2) definitely included in the deleted section, and what is our plan for eye screenings?
  4. 4.Would long-read sequencing provide any additional information about the structure of the ring that we don't already have from the microarray?
  5. 5.Based on the loss of the CHAMP1 or ZIC2 genes, what specific developmental or neurological specialists should we be seeing?

Questions For You

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References

References (22)
  1. 1

    Prenatal diagnosis of a fetus with mosaic ring chromosome 13: Case report and review of the literature.

    Hu XN, Li LL, Shi QY, et al.

    Taiwanese journal of obstetrics & gynecology 2021; (60(3)):554-558 doi:10.1016/j.tjog.2021.03.031.

    PMID: 33966748
  2. 2

    [Molecular cytogenetic diagnosis of a case with ring chromosome 18 syndrome].

    Lyu Y, Wang X, Zhang K, et al.

    Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics 2019; (36(10)):1010-1014 doi:10.3760/cma.j.issn.1003-9406.2019.10.015.

    PMID: 31598948
  3. 3

    Continuing role for classical cytogenetics: Case report of a boy with ring syndrome caused by complete ring chromosome 4 and review of literature.

    Burgemeister AL, Daumiller E, Dietze-Armana I, et al.

    American journal of medical genetics. Part A 2017; (173(3)):727-732 doi:10.1002/ajmg.a.38063.

    PMID: 28127864
  4. 4

    Compound phenotype in a girl with r(22), concomitant microdeletion 22q13.32-q13.33 and mosaic monosomy 22.

    Kashevarova AA, Belyaeva EO, Nikonov AM, et al.

    Molecular cytogenetics 2018; (11()):26 doi:10.1186/s13039-018-0375-3.

    PMID: 29736186
  5. 5

    Complex biology of constitutional ring chromosomes structure and (in)stability revealed by somatic cell reprogramming.

    Nikitina TV, Kashevarova AA, Gridina MM, et al.

    Scientific reports 2021; (11(1)):4325 doi:10.1038/s41598-021-83399-3.

    PMID: 33619287
  6. 6

    [Molecular cytogenetic analysis of a case with ring chromosome 3 syndrome].

    Zhang K, Song F, Zhang D, et al.

    Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics 2016; (33(6)):816-819 doi:10.3760/cma.j.issn.1003-9406.2016.06.015.

    PMID: 27984612
  7. 7

    Long read Nanopore sequencing identifies precise breakpoints of a de novo paracentric inversion that disrupt the MEIS2 gene in a Chinese girl with syndromic developmental delay.

    Tan J, Huang M, Ji X, et al.

    BMC pediatrics 2025; (25(1)):18 doi:10.1186/s12887-024-05267-z.

    PMID: 39789493
  8. 8

    Combining cytogenetic and genomic technologies for deciphering challenging complex chromosomal rearrangements.

    Michaelson-Cohen R, Murik O, Zeligson S, et al.

    Molecular genetics and genomics : MGG 2022; (297(4)):925-933 doi:10.1007/s00438-022-01898-y.

    PMID: 35488049
  9. 9

    Human ring chromosome registry for cases in the Chinese population: re-emphasizing Cytogenomic and clinical heterogeneity and reviewing diagnostic and treatment strategies.

    Hu Q, Chai H, Shu W, Li P

    Molecular cytogenetics 2018; (11()):19 doi:10.1186/s13039-018-0367-3.

    PMID: 29492108
  10. 10

    Molecular and Cytogenetic Characterization of a Fetus with Mosaic Ring Chromosome 13: A Very Rare Case.

    Zhao XR, Han X, Wang YL, Hu WJ

    Chinese medical journal 2017; (130(24)):3007-3008 doi:10.4103/0366-6999.220308.

    PMID: 29237938
  11. 11

    [Genetic features of a case with mosaic ring chromosome 4 and a review of the literature].

    Ma C, Wang Y, Zhen N, et al.

    Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics 2023; (40(1)):105-109 doi:10.3760/cma.j.cn511374-20210424-00358.

    PMID: 36585012
  12. 12

    Two Cases with Ring Chromosome 13 at either End of the Phenotypic Spectrum.

    Çakmaklı S, Çankaya T, Gürsoy S, et al.

    Cytogenetic and genome research 2017; (153(4)):175-180 doi:10.1159/000486775.

    PMID: 29518772
  13. 13

    13q deletion syndrome resulting from balanced chromosomal rearrangement in father: the significance of parental karyotyping.

    Dittner-Moormann S, Reschke M, Biewald E, et al.

    Molecular cytogenetics 2020; (13()):31 doi:10.1186/s13039-020-00500-7.

    PMID: 32760450
  14. 14

    Case report: Genetic diagnoses in a pediatric patient with retinoblastoma and comorbid global developmental delay: three distinct entities diagnosed by whole exome sequencing in a single patient.

    Chen J, Yang S, Wang H, et al.

    Frontiers in neuroscience 2024; (18()):1391596 doi:10.3389/fnins.2024.1391596.

    PMID: 39108315
  15. 15

    ZIC2 in Holoprosencephaly.

    Barratt KS, Arkell RM

    Advances in experimental medicine and biology 2018; (1046()):269-299 doi:10.1007/978-981-10-7311-3_14.

    PMID: 29442327
  16. 16

    Nasal fistula, epidermal cyst and hypernatremia in a girl presenting holoprosencephaly due to a rare ZIC2 point mutation.

    de Almeida IG, Kuratani DK, Gomes LM, et al.

    European journal of medical genetics 2020; (63(2)):103641 doi:10.1016/j.ejmg.2019.03.005.

    PMID: 30894326
  17. 17

    Reduced anogenital distance, hematuria and left renal hypoplasia in a patient with 13q33.1-34 deletion: case report and literature review.

    He X, Shen H, Fu H, et al.

    BMC pediatrics 2020; (20(1)):327 doi:10.1186/s12887-020-02205-7.

    PMID: 32616040
  18. 18

    Chromosome 13q deletion syndrome involving 13q31‑qter: A case report.

    Wang YP, Wang DJ, Niu ZB, Cui WT

    Molecular medicine reports 2017; (15(6)):3658-3664 doi:10.3892/mmr.2017.6425.

    PMID: 28393221
  19. 19

    [Analysis of a child with autosomal dominant mental retardation type 40 due to variant of CHAMP1 gene].

    Xu J, Li J, Jiao Z, et al.

    Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics 2023; (40(1)):47-52 doi:10.3760/cma.j.cn511374-20220517-00333.

    PMID: 36585000
  20. 20

    Cytogenetic and molecular characterization of a patient having infertility and mild intellectual disability with a very rare unstable ring chromosome 13.

    Kaya M, Suer I, Kalayci T, et al.

    Scottish medical journal 2022; (67(4)):173-177 doi:10.1177/00369330221114426.

    PMID: 35862016
  21. 21

    13q Deletion Syndrome Involving RB1: Characterization of a New Minimal Critical Region for Psychomotor Delay.

    Privitera F, Calonaci A, Doddato G, et al.

    Genes 2021; (12(9)) doi:10.3390/genes12091318.

    PMID: 34573300
  22. 22

    Deletion of Chromosome 13 due to Different Rearrangements and Impact on Phenotype.

    Bellucco FT, Rodrigues de Oliveira-Júnior H, Santos Guilherme R, et al.

    Molecular syndromology 2019; (10(3)):139-146 doi:10.1159/000497402.

    PMID: 31191202

This page explains genetic testing for Ring Chromosome 13 Syndrome for educational purposes. A medical geneticist is the best source for interpreting your child's specific microarray and karyotype reports.

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