Welcome to the Chromosome Anomaly Collection. This Collection contains examples of unbalanced chromosome abnormalities (UBCAs) without phenotypic effect. These are anomalous in the sense that the great majority of cytogenetically visible UBCAs do have phenotypic consequences which would be likely to come to medical attention. The Collection also includes the cytogenetically visible euchromatic variants that can now be regarded as part of the continuum of copy number variation in the human genome. A more detailed review has been published (Barber JCK, J Med Genet, 42, 609-629, 2005). Download review:

transmitted review jmg.pdf (603.9KB)


This Collection is designed to help Geneticists, Physicians and families by providing a summary of as many of the known examples as possible. While every attempt has been made to accurately replicate details from publications in full or in abstract, no responsibility for the accuracy of the information nor the decisions which might be made in the light of this Collection can be taken by the compiler who has constructed the attached Charts.

Structure of Register

The Collection has been divided into Unbalanced Chromosome Abnormalitites (UBCAs) and Euchromatic Variants (EVs). UBCAs involve the addition (duplication) or removal (deletion) of one of the two copies of each chromosomal segment present in normal diploid individuals. The majority of the established EVs involve variable regions of the genome in which pseudogene or gene segments are present in multiple copies that are visible under the light microscope when copy number is high enough.

The absence of phenotypic consequences can usually be established only when a parent and child with the same chromosome abnormality are both phenotypically normal, or, inferred when an affected child has an unaffected parent. Consequently, this Collection is almost entirely composed of transmitted chromosomal imbalances. These have been sub-divided into three major colour coded groups:


In Group I, both parents and children are phenotypically normal. The majority of these families are ascertained at prenatal diagnosis. These examples provide precedents for a normal phenotype associated with imbalance of a particular region. They cannot, however, guarantee that all other examples with the same chromosomal breakpoints will necessarily be free of phenotypic consequences. This may be especially true of de novo examples of the same abnormality. Nevertheless, five examples without direct transmission have been added to Group 1 including the dup(9) of Stumm et al (2002), the del(10) of Davis et al (1999), the dup(11) of Zarate et al (2007), the dup(13) of Rivera et al (1981) and the dup(18) of Starke et al (2001).


In Group II, the majority of families are ascertained because of the phenotype of the proband but parents with the same chromosome abnormality are unaffected. The chromosome abnormality may therefore be considered a coincidental finding. In a number of cases, however, genomic imprinting explains the presence or absence of a phenotype depending on the sex of the transmitting parent.


In Group III, for comparison, are directly transmitted chromosome abnormalities that generally have mild phenotypic consequences in both parents and children.


Accessing the Collection

UBCAs are illustrated on a chart with bars on the Idiograms which indicate the location and extent of each imbalance. Duplications are on the left hand side and deletions on the right hand side of each chromosome. Click on the bar to access the summary chart with further details and click on the abbreviated reference to obtain the full reference.

EVs are illustrated with arrows which point to the approximate location of the expanded segments in each case. Click on the arrow to access the summary chart with further details and click on the abbreviated reference to obtain the full references.


Unbalanced chromosome abnormality (UBCA) chart

Euchromatic Variant (EV) Chart


This Collection concentrates on unbalanced cytogenetically visible abnormalities but currently excludes supernumerary marker chromosomes, ring chromosomes and heterochromatic variants.

It should be remembered that phenotypic variability is the hallmark of many chromosomal and non-chromosomal conditions. The working conclusions that arise from this Anomaly Register can be summarised as:

1. most visible chromosome abnormalities have phenotypic consequences.

2. exceptions to this rule exist but are frequently unique to a single family.

3. only by gathering further examples will it be possible to identify regions of the genome that are consistently free of phenotypic consequences.


Contribute data:

Genetic centres are invited to submit additional examples that may make it possible to establish whether the phenotypically normal abnormality carriers represent the benign end of a spectrum of phenotypic effect, or, whether there are indeed cytogenetic abnormalities that are consistently free of phenotypic consequences. A Chromosome Anomaly Collection Submission Form is available here or from the compiler.



Other sources of useful information about chromosome abnormalities and variants can be found in the Borgaonkar Online Database or as hard copy in:

Schinzel A (2001) Catalogue of unbalanced chromosome aberration in man. 2nd ed, de Gruyter, ISBN 3-11-011607-3
Borgaonkar DS (1997) Chromosomal variation in man; a catalogue of chromosomal variants and anomalies. 8th ed, Wiley, ISBN 0-471-24332-9

Other databases that may overlap with the Chromosome Anomaly Collection include:

The European Cytogenetic Association Register of Unbalanced Chromosome Abnormalities (ECARUCA) which contains details of thousands of published cytogenetic imbalances and is prospectively gathering rare cytogenetic and molecular cytogenetic aberrations. On-line registration and submission can be carried out at www.ecaruca.net/.

The DatabasE of Chromosomal Imbalance and Phenotype in Humans using Ensemble Resources (DECIPHER) which has been inspired by the need to distinguish clinically significant imbalances from transmitted imbalances or polymorphisms detected using micro-arrays. On-line registration and submission can be carried out at www.sanger.ac.uk/PostGenomics/decipher.

The unprecedented degree of large scale copy number variation found with array techniques is also being gathered in:

1. the Database of Genomic Variants (http://projects.tcag.ca/variation/) and

2.  the Structural Variation Database  (http://humanparalogy.gs.washington.edu/structuralvariation/).

The long established UK Association of Clinical Cytogeneticists (ACC) Chromosome Abnormality Database (CAD) is also now on-line for registration and free searches


This Collection has been compiled by Dr John Barber who can be contacted at:

National Genetics Reference Laboratory (Wessex)
Salisbury NHS Foundation Trust

Salisbury District Hospital
Tel: +44 (0)1722 429080
Fax: +44 (0)1722 338095
e-mail: john.barber@salisbury.nhs.uk


Acknowledgement The help of Gemma Watkins, Carolyn Wallis, Kelley Gardner and Mac Gardner in the construction of this entry is gratefully acknowledged. Viv Maloney kindly constructed the chromosomal idiograms.

Submission Form


National Genetics Reference Laboratory (Wessex)
Salisbury District Hospital