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[[File:Molecular Diagnostics.jpg|right|426px]]In 2018, the World Health Organization (WHO) noted the following about modern genetic testing<ref name="WHOGenetic">{{cite web |url=https://www.who.int/genomics/professionals/laboratories/en/ |archiveurl=https://web.archive.org/web/20181003114819/http://www.who.int/genomics/professionals/laboratories/en/ |title=Genetic laboratories and clinics |work=Human Genomics in Global Health |publisher=World Health Organization |archivedate=03 October 2018 |accessdate=18 November 2021}}</ref>:
Cytogenetics is a subcategory of genetics that specifically studies chromosomes and their structures. "Trained cytogeneticists examine the number, shape, and staining pattern of these structures using special technologies. In this way, they can detect extra chromosomes, missing chromosomes, missing or extra pieces of chromosomes, or rearranged chromosomes."<ref name="AACCGenetic19" /> Some diseases occur as the result of these chromosomal anomalies; for example, amplification of a particular gene in breast cancer or translocation of part of a chromosome in chronic myelogenous leukemia may be spotted with cytogenetic techniques.<ref name="AACCGenetic19" />


<blockquote>Prior to the development of modern genetic technologies, genetic services were limited to genetic counselling, where health professionals would attempt to characterize the genetic contribution of diseases based on family histories. With the discovery of DNA, genetic services have dramatically increased in quality and scope. Increasingly sophisticated technologies now permit new methodology and high quality preparations, ensuring greater accuracy in diagnosis.</blockquote>
The cytogenetics laboratory depends on several analytical techniques to make these sorts of genetic discoveries in a patient. Methods include chromosome analysis or karyotyping, fluorescence ''in situ'' hybridization (FISH), and microarray-based assays such as comparative genomic hybridization.<ref name="AACCGenetic19" /><ref name="MayoClinicCyto">{{cite web |url=https://www.mayoclinic.org/departments-centers/laboratory-medicine-pathology/overview/specialty-groups/laboratory-genetics/cytogenetics-laboratory |title=Cytogenetics Laboratory |work=Departments and Centers: Laboratory Medicine and Pathology |publisher=Mayo Clinic |accessdate=18 November 2021}}</ref><ref name="YaleCyto">{{cite web |url=https://medicine.yale.edu/lab/cytogenetics/testing/ |title=Cytogenetics Lab Tests |work=Cytogenetics Lab |publisher=Yale School of Medicine |accessdate=18 November 2021}}</ref> Karyotyping involves the separation of whole chromosomes from the nuclei of cells that have been stained with special dyes, cutting and arranging the resulting imagery of those chromosomes, and examining the results. FISH uses special "probes" that fluoresce gene segments of chromosomes. The position and number of the fluoresced gene segments is then analyzed for abnormalities.<ref name="AACCGenetic19" /> And the comparative genomic hybridization assay uses a complicated process of using a "competitive" form of FISH that compares two DNA sources, which are denatured so they are single-stranded, and hybridizes the two samples in a 1:1 ratio to a normal metaphase spread of chromosomes.<ref name="WeissComp99">{{cite journal |title=Comparative genomic hybridization |journal=Molecular Pathology |author=Weiss, M.M.; Hermsen, M.A.; Meijer, G.A. et al. |volume=52 |issue=5 |pages=243–51 |year=1999 |doi=10.1136/mp.52.5.243 |pmid=10748872 |pmc=PMC395705}}</ref>


A genetic diagnostics lab uses genetic testing to evaluate DNA in the search for a genetic cause for symptoms or a disease. The lab may also have other responsibilities or goals, including interpreting results for physicians, detecting mutations, developing new analytical methods, and improving patient care through its discoveries.<ref name="WHOGenetic" /><ref name="UPennTheGenetic">{{cite web |url=https://genetics.med.upenn.edu/cores/genetic-diagnostic-laboratory/ |title=Genetic Diagnostic Laboratory |work=Genetics - Perelman School of Medicine |publisher=University of Pennsylvania |accessdate=18 November 2021}}</ref>  
Like a normal medical diagnostic laboratory, the cytogenetics laboratory must follow a set of good practices, many of which are similar to the medical diagnostic lab. However, additional considerations to good practice specific to the cytogenetics laboratory are typically required, particularly in being assessed for accreditation. In Australia, for example, the National Pathology Accreditation Advisory Council (NPAAC) makes recommendations on the accreditation of laboratories providing cytogenetic services.<ref name="NPAACRequire13">{{cite book |url=https://www1.health.gov.au/internet/main/publishing.nsf/Content/76FFC342EA4F4CCBCA257BF0001D7A2A/$File/V0.22%20Cytogenetics.pdf |format=PDF |title=Requirements for Cytogenetic Testing, Third Edition |author=National Pathology Accreditation Advisory Council |publisher=Commonwealth of Australia |edition=3rd |year=2013 |isbn=9781742419572 |accessdate=18 November 2021}}</ref> The College of American Pathologists (CAP) does something similar with its Cytogenetics Checklist for its CAP Accreditation Program.<ref name="CAPCyto17">{{cite web |url=https://elss.cap.org/elss/ShowProperty?nodePath=/UCMCON/Contribution%20Folders/DctmContent/education/OnlineCourseContent/2017/LAP-TLTM/checklists/cl-cyg.pdf |format=PDF |title=Cytogenetics Checklist |author=College of American Pathologists |date=21 August 2017 |accessdate=18 November 2021}}</ref>
 
The WHO classifies genetic testing into five broad categories<ref name="WHOGenetic" />:
 
#Carrier identification screening: a test that checks one or more individuals for whether or not they carry a genetic marker for a specific disease (e.g., cystic fibrosis)
#Prenatal diagnostic testing: a series of tests using routine ''in vitro'' fertilization methods when a gestating child is thought to have a genetically caused disease (e.g., Down syndrome)
#Newborn screening: one or more preventative health tests for treating a newborn early when treatment is available (e.g., congenital hypothyroidism)
#Late-onset disorder testing: testing that occurs later in life to determine susceptibility of an individual to a particular disease (e.g., cancer and heart disease)
#Identity testing: testing that "involves profiling the individuals genetic information from DNA test results of genetic markers in order to locate characteristics unique to the individual" (often used in forensic and criminal investigations)
 
As for the techniques used in genetic testing, the American Association for Clinical Chemistry (AACC) has five categories of techniques: [[polymerase chain reaction]] (PCR), DNA sequencing, microarrays, gene expression profiling, and cytogenetics. (For more on cytogenetics, see the following subsection.) The PCR technique is a copying technique that "enables specific genes or regions of interest to be detected or measured." [[DNA sequencing]] (e.g., [[next-generation sequencing]] or NGS) allows scientists to identify changes or variations in the way DNA is arranged that may indicate a disorder. Microarray testing has multiple uses, among them identifying duplications, deletions, or identical sections in DNA, which may indicate a propensity for a particular disease. Gene expression profiling looks at the genes of cells and determines if they are actively making proteins or not for aiding in prognosis, recurrence, and other types of diagnostic indicators for disease.<ref name="AACCGenetic19">{{cite web |url=https://www.testing.com/genetic-testing-techniques/ |title=Genetic Testing Techniques |work=Testing.com |publisher=OneCare Media |date=09 November 2021 |accessdate=18 November 2021}}</ref>


==References==
==References==
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{{Reflist|colwidth=30em}}

Revision as of 23:25, 21 January 2022

Cytogenetics is a subcategory of genetics that specifically studies chromosomes and their structures. "Trained cytogeneticists examine the number, shape, and staining pattern of these structures using special technologies. In this way, they can detect extra chromosomes, missing chromosomes, missing or extra pieces of chromosomes, or rearranged chromosomes."[1] Some diseases occur as the result of these chromosomal anomalies; for example, amplification of a particular gene in breast cancer or translocation of part of a chromosome in chronic myelogenous leukemia may be spotted with cytogenetic techniques.[1]

The cytogenetics laboratory depends on several analytical techniques to make these sorts of genetic discoveries in a patient. Methods include chromosome analysis or karyotyping, fluorescence in situ hybridization (FISH), and microarray-based assays such as comparative genomic hybridization.[1][2][3] Karyotyping involves the separation of whole chromosomes from the nuclei of cells that have been stained with special dyes, cutting and arranging the resulting imagery of those chromosomes, and examining the results. FISH uses special "probes" that fluoresce gene segments of chromosomes. The position and number of the fluoresced gene segments is then analyzed for abnormalities.[1] And the comparative genomic hybridization assay uses a complicated process of using a "competitive" form of FISH that compares two DNA sources, which are denatured so they are single-stranded, and hybridizes the two samples in a 1:1 ratio to a normal metaphase spread of chromosomes.[4]

Like a normal medical diagnostic laboratory, the cytogenetics laboratory must follow a set of good practices, many of which are similar to the medical diagnostic lab. However, additional considerations to good practice specific to the cytogenetics laboratory are typically required, particularly in being assessed for accreditation. In Australia, for example, the National Pathology Accreditation Advisory Council (NPAAC) makes recommendations on the accreditation of laboratories providing cytogenetic services.[5] The College of American Pathologists (CAP) does something similar with its Cytogenetics Checklist for its CAP Accreditation Program.[6]

References

  1. ↑ 1.0 1.1 1.2 1.3 Cite error: Invalid <ref> tag; no text was provided for refs named AACCGenetic19
  2. ↑ "Cytogenetics Laboratory". Departments and Centers: Laboratory Medicine and Pathology. Mayo Clinic. https://www.mayoclinic.org/departments-centers/laboratory-medicine-pathology/overview/specialty-groups/laboratory-genetics/cytogenetics-laboratory. Retrieved 18 November 2021. 
  3. ↑ "Cytogenetics Lab Tests". Cytogenetics Lab. Yale School of Medicine. https://medicine.yale.edu/lab/cytogenetics/testing/. Retrieved 18 November 2021. 
  4. ↑ Weiss, M.M.; Hermsen, M.A.; Meijer, G.A. et al. (1999). "Comparative genomic hybridization". Molecular Pathology 52 (5): 243–51. doi:10.1136/mp.52.5.243. PMC PMC395705. PMID 10748872. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC395705. 
  5. ↑ National Pathology Accreditation Advisory Council (2013) (PDF). Requirements for Cytogenetic Testing, Third Edition (3rd ed.). Commonwealth of Australia. ISBN 9781742419572. https://www1.health.gov.au/internet/main/publishing.nsf/Content/76FFC342EA4F4CCBCA257BF0001D7A2A/$File/V0.22%20Cytogenetics.pdf. Retrieved 18 November 2021. 
  6. ↑ College of American Pathologists (21 August 2017). "Cytogenetics Checklist" (PDF). https://elss.cap.org/elss/ShowProperty?nodePath=/UCMCON/Contribution%20Folders/DctmContent/education/OnlineCourseContent/2017/LAP-TLTM/checklists/cl-cyg.pdf. Retrieved 18 November 2021. 
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