Interpretive Handbook

Test 80602 :
Chromosome Anomalies, Unspecified Miscellaneous with Chromosome-Specific FISH Probes

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Conventional cytogenetic studies can identify the presence of chromosome abnormalities and the presence or absence of most mosaic conditions. Conventional cytogenetic studies utilize a variety of staining techniques to identify each chromosome. With these methods, structural or numeric chromosome abnormalities are detected in approximately 11% of peripheral blood specimens referred to our Cytogenetic Laboratory from patients with congenital disorders.


In approximately 2% of these chromosomally abnormal cases, the genetic makeup of the chromosome anomaly can be identified, but not completely characterized, by conventional techniques alone. For malignant disorders, the proportion of specimens with unresolvable chromosome abnormalities is much higher. In our experience, the use of FISH with chromosome-specific paint probes (collections of unique DNA sequences for specific chromosomes), locus-specific probes, and alpha-satellite probes can help establish the genetic makeup of a high proportion of chromosome abnormalities. This includes abnormalities that cannot be accurately characterized by conventional methods such as unusual structural alterations, questionable mosaicism of an abnormality, and unbalanced chromosome abnormalities such as deletions, duplications, and translocations that cannot be resolved by studies on other family members. Scoring chromosomal aneuploidy abnormalities by FISH is generally easier than by conventional cytogenetic methods and can be done by use of either interphase or metaphase cells. Thus, large numbers of cells can be scored to more accurately establish the frequency of chromosome abnormalities.


We recommend that conventional chromosome analysis be performed first to establish the constitutional karyotype and determine whether or not the patient has chromosome mosaicism.

Useful For Suggests clinical disorders or settings where the test may be helpful

As an adjunct to conventional chromosome studies, to resolve unusual or complex structural alterations, questionable mosaicism, and unbalanced chromosome abnormalities that cannot be resolved by studies on other family members


Diagnosing certain disorders caused by a deletion or duplication of a given chromosome region


Identifying unbalanced structural abnormalities in cases where this information is needed more rapidly than conventional chromosome analysis can supply (eg, situations where genetic counseling is needed quickly to decide treatment, but conventional cytogenetic studies would require studying multiple family members)


Establishing the origin and centromeric makeup of dicentric or marker chromosomes


In suboptimal chromosome preparations, FISH can help confirm the results of conventional chromosome analysis


Determining whether a child's deletion or duplication detected via array comparative genomic hybridization (aCGH) is de novo or inherited

Interpretation Provides information to assist in interpretation of the test results

An interpretive report is provided.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Structural alterations involving highly repetitive DNA sequences such as the chromosome 1 p-arm terminal region and pericentromeric regions of most chromosomes may not show bright fluorescence with some of these probes.


It may not always be possible to detect chromosome segments that are smaller than 1.5 megabases. Thus, subtle structural abnormalities may not be detected with this method.


The alpha-satellite probes are not available for every chromosome. Some of the alpha-satellite probes cross-hybridize with other chromosomes (eg, chromosomes 13/21, 14/22, and 1/5/19).


Both chromosome-specific paint probes and alpha-satellite probes work best when the cytogenetic preparations are <4 weeks old.


Normal results do not rule out the possibility of subtle or variant abnormalities.


Normal results for any FISH study do not rule-out abnormalities other than those being specifically targeted.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

An interpretive report will be provided.

Clinical References Provides recommendations for further in-depth reading of a clinical nature

1. Remstein ED, Dogan A, Einerson RR, et al: The incidence and anatomic site specificity of chromosomal translocations in primary extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) in North America. Am J Surg Pathol 2006 Dec;30(12):1546

2. Fonseca R, Blood E, Rue M, et al: Clinical and biologic implications of recurrent genomic aberrations in myeloma. Blood 2003 Jun 1;101(11):4569-4575

3. Van Dyke DL, Shanafelt TD, Call TG, et al: A comprehensive evaluation of the prognostic significance of 13q deletions in patients with B-chronic lymphocytic leukaemia. Br J Haematol 2010;148:544-550

4. Wiktor A, Van Dyke DL: FISH analysis helps identify low-level mosaicism in Ullrich-Turner syndrome patients. Genet Med 2004;6:132-135