What is the cytogenetic study? Cytogenetic analysis and early diagnosis of diseases
Cytogenetic analysis (or chromosome map or karyotype) is the study of the chromosomes of cells
Chromosomes contain genes that are made up of DNA, the molecule that contains all the information necessary for the ‘construction’ of the individual and the functioning of the organism.
In the cells of human beings there are 46 chromosomes: 23 chromosomes come from the father with the spermatozoon and 23 from the mother with the egg cell.
Spermatozoa and egg cells are germ cells and are the only ones that contain only 23 chromosomes.
If the sperm carries the X chromosome a female will be born, if it carries the Y chromosome a male will be born.
The karyotype of a normal female will therefore be 46, XX while that of a male 46, XY.
In order to study chromosomes, it is necessary to use culture techniques as it is only during cell division that they can be visualised.
What is the purpose of a cytogenetic study?
The cytogenetic study is used to verify that there are no alterations in the number and/or structure of chromosomes that may be responsible for diseases characterised by mental retardation (e.g. Down syndrome), infertility/sterility (e.g. Turner and Klinefelter syndromes), psychomotor and speech, growth and developmental retardation.
Repeated early miscarriage may also be the result of a chromosomal error in one of the parents (3-5% of cases).
When is a cytogenetic study appropriate?
Prenatal cytogenetics
It is carried out in pregnancies in which there is an increased risk of chromosomal abnormalities in the foetus: maternal age 35 years or older (before the birth of the child), child with a chromosome number error, parents with structural rearrangements that show no clinical signs, parents with sex chromosome number errors (e.g. 47,XXX; 47,XXY ), foetal abnormalities revealed by ultrasound, indications from biochemical tests (e.g. bi-test), repeated miscarriages.
Transabdominal villus sampling can be performed during the first trimester of pregnancy (9-12 weeks) or amniocentesis during the second trimester (15-18 weeks).
For chorionic villus sampling, cells are taken from the placenta (chorionic villi) that have the same origin (and therefore the same genetic heritage) as those of the foetus, while amniocentesis studies foetal cells found in the amniotic fluid (amniocytes).
Postnatal cytogenetics
The karyotype study is carried out in patients with suspected chromosomal syndrome, parents and relatives of individuals with chromosomal abnormalities, parents of malformed individuals or individuals with suspected chromosomal syndrome who have died without a diagnosis, if mental retardation and/or congenital defects, growth retardation, stillborn infants, couples with repeated miscarriages, male infertility, females with primary or secondary amenorrhoea (absence or interruption of the menstrual cycle) are found.
CHILD HEALTH: LEARN MORE ABOUT MEDICHILD BY VISITING THE BOOTH AT EMERGENCY EXPO
Cytogenetics on abortion material
Approximately 15-20% of all recognised pregnancies result in a miscarriage and more than 50% have an altered chromosome number and/or structure that is the cause of pregnancy termination.
The cytogenetic study of abortion tissues is therefore of fundamental importance in understanding the cause of pregnancy termination, and of support to the couple (since in most cases the chromosomal error is purely coincidental and does not entail an increased risk that the event will recur).
Cytogenetics of tumours
Cytogenetic analysis can also be performed to study tumours, both haematological (e.g. leukaemia) and solid (e.g. lung, breast, liver, bladder).
Certain chromosomal rearrangements are ‘tumour-specific’ and thus allow a correct diagnosis in the face of clinical suspicion or doubt.
For example, the finding of the Philadelphia chromosome in a bone marrow aspirate of a patient with suspected leukaemia allows the diagnosis of chronic myeloid leukaemia; or the presence of the t(X;18) translocation in a cell culture prepared from a solid tumour biopsy allows the diagnosis of Sinovial Sarcoma.
New technologies: Fluorescent In Situ Hybridization (FISH)
The development of sophisticated techniques known as ‘Molecular Cytogenetics’, such as Fluorescent In Situ Hybridization (FISH), makes it possible to carry out more in-depth cytogenetic studies as it allows the localisation of a specific DNA sequence on fixed preparations of chromosomes, interphase nuclei and tissue sections, obtained from any type of biological material (blood, biopsies, amniotic fluid, gametes), whether fresh, cryopreserved or paraffin-embedded.
The FISH technique is based on DNA’s property of reversible denaturation (opening of the double helix) and involves the binding of a DNA fragment specific to the region of interest – labelled with fluorescent compounds (probe) – to the complementary DNA sequence of the preparation that has been fixed and mounted on a glass slide: the chromosomal region of interest is thus easily identified under a fluorescence microscope.
FISH represents an indispensable complement to traditional cytogenetics as it is characterised by its greater power of resolution: it allows the characterisation of chromosome abnormalities of a number and structure that cannot be defined by classical cytogenetic techniques and the identification of cryptic rearrangements that are not visible even after high-resolution banding.
FISH is not routinely applied to karyotype analysis, but only in selected cases based on specific diagnostic suspicions or to investigate certain cytogenetic abnormalities.
One of the most recent applications is in the field of oncology: in many cases, especially for solid tumour cultures, cell growth and division cannot be obtained and therefore chromosomes cannot be highlighted and analysed.
Moreover, the level of resolution of the study carried out with traditional cytogenetics does not allow anomalies to be identified that might only affect one gene.
Since the year 2000, DNA probes have been developed that are able to recognise specific abnormalities, for example in bladder cancer, for which four probes are used that recognise chromosomes 3, 7, 17 and nine labelled with different fluorochromes (Multicolour FISH).
FISH identifies tumour-typical chromosome abnormalities before there is evidence of disease on cystoscopic investigation or positivity of other diagnostic markers such as CTM (malignant tumour cells).
In 2001 the test was approved by the US Food and Drug Administration (FDA) for monitoring disease recurrence in patients who had already been diagnosed with cancer and had undergone removal surgery and/or BCG therapy, and in 2004 for diagnosis in patients with haematuria.
FISH can also provide information on the most appropriate therapy for a certain type of tumour in a given patient (Targeted Therapy)
It is known, for example, that breast cancer patients who have a positive FISH for amplification of a gene called HER-2/neu, whose protein is exposed on the tumour cell membrane, respond to therapy with a particular drug, trastuzumab, an antibody that binds to the receptor and neutralises it (immunological therapy).
The test is called PATHVYSION® and is approved by the FDA.
FISH can also be used to study the amplification of another gene called EGFR, in lung and colon cancer.
Here too, different drugs can be used depending on whether or not amplification of the gene is found in the patient’s tumour.
In these cases, therapy is not using antibodies but small molecules that inhibit cell division (biological therapy).
New frontiers are opening up with the application of FISH for other tumour types such as melanoma, where differential diagnosis with dysplastic nevus is particularly difficult if based solely on morphological criteria.
Given its high sensitivity, specificity and anticipatory power, the FISH technique is particularly effective in the study of both haematological and solid tumours.
In particular, it not only has diagnostic/prognostic value but is fundamental in the choice of therapy based on the tumour’s genomic profile.
Read Also
Emergency Live Even More…Live: Download The New Free App Of Your Newspaper For IOS And Android
Rare Diseases: Rothmund-Thomson Syndrome
Rare Diseases: Russian Economist Anatoly Chubais Diagnosed With Guillain Barré Syndrome
Ultrarare Diseases: First Guidelines For Malan Syndrome Published
Rare Genetic Diseases: Long QT Syndrome
Rare Diseases: Von Hippel-Lindau Syndrome
Zika Linked To Guillain-Barre Syndrome In New Study
Rare Diseases: Septo-Optic Dysplasia
Rare Diseases: Congenital Hyperinsulinism
Foot Deformities: Metatarsus Adductus Or Metatarsus Varus
Progeria: What Is It, Symptoms, Causes, Diagnosis And Possible Treatment
Rare Diseases: 5p Deletion Syndrome (‘Cri-Du Chat’ Syndrome)