cytogenetics

Cytogenetics is the study of the numerical and structural states of chromosomes and their role in heredity. The science of cytogenetics emerged in the early twentieth century, when scientists realized that chromosomes were the physical carriers of genes. Researchers revealed the theory of chromosome inheritance with their observations. This groundbreaking theory was grounded in cytologists’ detailed observations of chromosome movements during mitosis and meiosis, showing that chromosome behavior could explain Mendelian principles of inheritance. In the early years, scientists interested in cytogenetics had a difficult time distinguishing between individual chromosomes, but over the years they continued to improve the conditions for preserving and staining chromosomes up to the reproducible standards expected in clinical cytogenetics. (Looking back, it seems incredible that the human chromosome number was not established until 1955.) In today’s procedures, metaphase chromosomes are treated with dyes that create different banding patterns, and then the chromosome pairs are placed in a standard format known as a karyotype. Among members of a species, karyotypes are fairly uniform; this has made it possible for cytogeneticists to detect various aberrations in chromosome number and structure that are associated with disease states and developmental defects.

In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome consists of DNA tightly coiled many times around proteins called histones that support its structure. In short, chromosomes are a packaged form of DNA. A healthy human karyotype contains 22 pairs of autosomes and one pair of sex chromosomes. In chromosome analysis, the existing chromosomes are analyzed numerically and structurally in line with all these principles and reported.

What is prenatal (prenatal) cytogenetic diagnostic test?

Prenatal cytogenetic analysis is a diagnostic test performed in patients with prenatal diagnosis indications. Prenatal chromosomal analysis can be done by chorionic villus sampling (CVS) or amniocentesis. Typically, CVS is done during the first trimester of pregnancy at 10-12 weeks gestation, while amniocentesis is done at 14-18 weeks. It is done during pregnancy weeks. Percutaneous umbilical blood sampling (cordocentesis) is a prenatal diagnosis method that is generally used in cases where fetal blood is preferred. Cordocentesis is usually done after the 20th week of pregnancy.

Chromosome analysis from the amniocentesis material results in 3 or 4 weeks after the sample reaches the laboratory. Similarly, cytogenetic examinations of chorionic villus samples are also concluded within the same period. During this time, a prenatal rapid FISH study can be performed in addition to karyotype analysis to reduce concerns. The prenatal rapid FISH study is a quick and simple way to detect trisomy 13, 18 or 21 as well as to determine the fetal sex chromosome complement.

What are the Indications for Prenatal Chromosome Analysis?

  • Advanced maternal age (35 years and above)
  • Increased risk factor in biochemical screening tests (3 in 2 screening tests)
  • Abnormal USG findings
  • Poor obstetric history (recurrent pregnancy loss)
  • Balanced translocation carrier parent
  • History of a child with chromosomal anomalies

What should be the material for the test?

When the patient’s indication is determined, the obstetrician takes samples from the patient with 4 different invasive methods in accordance with the week of pregnancy.

  • 9-11. chorionic villi (CVS) in sterile transport medium at gestational week,
  • 16-19. Amniotic fluid in sterile non-sealed syringe at gestational week
  • 19-22. Cord blood in a sterile injector with heparin or in a tube with heparin at the gestational week
  • Example of miscarriage material in sterile transport medium in terminated pregnancy

What is Postnatal Cytogenetic Diagnostic Test?

Peripheral blood, bone marrow and skin etc. Chromosome studies obtained by short-term or long-term cell culture from tissue samples are called Postnatal Cytogenetic Diagnosis. Samples taken from patients are analyzed considering their indications and the results are interpreted. The patient is given a report accompanied by genetic counseling. The duration of these procedures is usually around 3 weeks.

What are postnatal (Postnatal) cytogenetic diagnostic tests?

• Chromosome analysis from peripheral blood culture
• Skin etc. cell culture and chromosome analysis from tissues
• Chromosome analysis from bone marrow

To whom should it be done?

In the presence of indications determined by the clinicians of the relevant branches, it is applied to patients with developmental delay, cases with congenital anomalies, couples with recurrent pregnancy losses and reproductive problems, individuals in the diagnosis and treatment process of hematological diseases, and cases with cancer diagnosis and treatment protocols.

What are the Indications for Postnatal Chromosome Analysis?

  • Congenital dysmorphic findings
  • Developmental Retardation (Mental motor retardation)
  • Recurrent Pregnancy Loss
  • Pre-in vitro fertilization screening
  • Indeterminate (Ambigius) genitalia
  • Short stature
  • Gender Developmental Disorders (Lack of hair growth, amenorrhea, Testicular Developmental Problem)
  • Early Menopause
  • Infertility (Azo-oligospremia)
  • Family History of Baby with Chromosomal Anomaly
  • Hematological Diseases / Malignancies

What should be the material for the test?

  • Venous blood in heparin syringe or heparin tube
  • Bone marrow in a heparin syringe or tube with heparin
  • Skin biopsy specimen in transport medium

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