Chromosome Analysis, for Congenital Disorders, Blood
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Chromosome abnormalities cause a wide range of disorders associated with birth defects and congenital diseases. Congenital chromosome studies are done on blood for a wide variety of indications including mental retardation, failure to thrive, possible Down syndrome, delayed puberty or primary amenorrhea (Turner syndrome), frequent miscarriages, infertility, multiple congenital anomalies, sex determination, and many others.
A chromosomal microarray study (CMAC / Chromosomal Microarray, Congenital Blood) is recommended as the first-tier test (rather than a congenital chromosome study) to detect clinically relevant gains or losses of chromosomal material for individuals with multiple anomalies not specific to well-delineated genetic syndromes, individuals with apparently nonsyndromic developmental delay or intellectual disability, and individuals with autism spectrum disorders.
Diagnosis of a wide variety of congenital conditions
Identification of congenital chromosome abnormalities, including aneuploidy (ie, trisomy or monosomy) and structural abnormalities
When interpreting results, the following factors need to be considered:
-Some chromosome abnormalities are balanced (no apparent gain or loss of genetic material) and may not be associated with birth defects. However, balanced abnormalities often cause infertility and, when inherited in an unbalanced fashion, may result in birth defects in the offspring.
-A normal karyotype (46,XX or 46,XY with no apparent chromosome abnormality) does not eliminate the possibility of birth defects such as those caused by submicroscopic cytogenetic abnormalities, molecular mutations, and environmental factors (ie, teratogen exposure).
It is recommended that a qualified professional in Medical Genetics communicate all abnormal results to the patient.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This test is not appropriate for acquired hematologic disorders, including the following malignancies: chronic myelocytic leukemia, acute myelocytic leukemia, acute lymphocytic leukemia, chronic lymphocytic leukemia, lymphoma, and leukemia.
Some congenital disorders require special culture methods:
-For Bloom syndrome, order SCE / Chromosome Analysis, Sister Chromatid Exchange (SCE) for Bloom Syndrome, Blood
It is important to provide the suspected diagnosis and clinical features to ensure the most appropriate type of cytogenetic study is performed.
- Cell lysis caused by forcing the blood quickly through the needle
- Use of an improper anticoagulant (sodium heparin is best) or improperly mixing the blood with the anticoagulant
- Excessive transport time
- Inadequate amount of blood (we recommend at least 5 mL for adults, 2 mL for children, and 1 mL for infants)
- Exposure of the specimen to temperature extremes
- T lymphocytes that do not respond to mitogens used to stimulate T cells to undergo mitosis (rare)
- Chromosomal mosaicism may be missed due to statistical sampling error (rare)
- Subtle structural chromosome abnormalities can occasionally be missed
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.
46,XX or 46,XY. No apparent chromosome abnormality.
An interpretive report will be provided.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Manning M, Hudgins L: Professional Practice and Guidelines Committee. Array-based technology and recommendations for utilization in medical genetics practice for detection of chromosomal abnormalities. Genet Med 2010;12(11):742-745
2. Dewald GW: Modern methods of chromosome analysis and their application in clinical practice. In Clinical Laboratory Annual. Vol 2. Edited by HA Homburger, JG Batsakis. Appleton-Century-Crofts, 1983, pp 1-29
3. Barch MJ, Knutsen T, Spurbeck JL: The AGT Cytogenetics Laboratory Manual. Third edition. 1997