Chromosome studies, Blood Chromosome Analysis, Cytogenetics, Chromosome Karyotyping

Sample

1. The test can be performed on almost any tissue, including:
   1. Blood. Leucocytes are a good source and can get easily the sample from the vein.
   2. Bone marrow.
   3. Placenta.
   4. Amniotic fluid (amniocentesis).
   5. Chorionic villous sample.
   6. Smears from the buccal mucosa are easy but not as good as other sources.
   7. Skin.
   8. Tumor cells.

Purpose of the test (Indications):

1. This test is done to find a chromosomal defect that may lead to or is a risk of the disease.
2. Count the number of chromosomes.
3. Look for structural changes in chromosomes.
4. On a couple that has a history of miscarriage or infertility. Both parents need chromosomal studies.
5. In the case of two consecutive abortions.
6. When there is more than one organ abnormality in the infant.
7. In the case of developmental delay, mental retardation, and in growth retardation.
8. To advise on ambiguous genitalia.
9. In the case of mental retardation and or developmental delay when the cause is not known.
10. In the case of the family history of chromosomal translocation.
11. To examine any child or baby who has unusual features or developmental delays like:
    1. Mental retardation.
    2. Growth retardation.
    3. Delayed puberty.
    4. Hypogonadism.
    5. Primary amenorrhoea.
    6. Ambiguous genitalia.
    7. Neoplasm.
    8. Prenatal diagnosis of congenital disease.
    9. Turner syndrome.
    10. Klinefelter syndrome.
    11. Down syndrome.
12. In the case of spontaneous abortion, stillbirth, and neonatal death.
13. The bone marrow or blood test can be done to identify the Philadelphia chromosome, which is found in about 85% of people with chronic myelogenous leukemia (CML).
14. The amniotic fluid test is done to check a developing baby for chromosome abnormality.

Effect of chromosomal abnormalities:

1. There may be spontaneous abortion.
2. There may be 50% chromosomal abnormalities in the fetus and out of these > 90%  will die during the gestational period.
3. 50% of the abortions, 7% of the stillbirth, and 0.5% of the neonates have chromosomal abnormalities.

Pathophysiology

1. Each human somatic cell has 46 chromosomes in pairs of 23.
   1. These are diploid cells, the fetus gets one chromosome from each of the parents, one from the father and one from the mother.
   2. It means that the donation of one chromosome from each of the parents.
   3. 22 chromosomes are identical called homologous (autosomes).
   4. One pair consists of XX in females and XY in males.
   5. Chromosomes number 1 is the longest.
      1. Chromosomes number 22 is the shortest.
      2. Chromosomes can not be distinguished from the length because of the variation from person to person.
      3. Therefore the position of the centromere is used to classify chromosomes.
      4. Chromosomes are stained with the Giemsa stain which gives distinctive chromosomes bands.

1. Karyotyping refers to the arrangement and pairing of cell chromosomes in order from the largest (longest) to the smallest (shortest)  to analyze their number and structure.
   1. Karyotyping is the number and appearance of chromosomes in the nucleus of a eukaryotic cell.
   2. Karyotyping refers to the arrangement of cell chromosomes, their number, and structure.

3. Karyotypes describe the number of chromosomes, and what they look like under a light microscope.
4. The normal karyotype of chromosomes consists of:
   1. 22 pairs of autosomal chromosomes (XX).
   2. One pair consists of a sex chromosome, XY for the male and XX for the female.
      1. The somatic cell with more or less than 46 chromosomes is called aneuploidy.
      2. More than 46 chromosomes are called hyperploidy.
      3. Less than 46 chromosomes are called hypoploidy.
5. Chromosomal abnormalities may be:
   1. Congenital.
   2. Acquired.
      1. Chromosomes abnormalities are the common cause of mental retardation and miscarriage.
      2. Roughly 1 in 12 conceptions has a chromosomal abnormality.
      3. Most of these fetuses don’t survive to term and 50% of first trimester fetuses abort and have major chromosomal abnormalities.
6. Karyotype (Chromosomal) abnormalities occur because of:
   1. Duplication.
   2. Deletion denoted by del. This may take place on the short or long arm.
   3. Translocation denoted by t.
   4. Reciprocation.
   5. Genetic rearrangement.

Normal

• Females = 44 autosomes + 2 sex chromosomes (XX) = Karyotype = 46, XX
• Males = 44 autosomes + 2 sex chromosomes (XY) = karyotype = 46, XY

The procedure of chromosomal analysis:

1. The cells are stimulated to divide.
   1. Lymphocytes can be stimulated by the phytohemagglutinin.
2. Add Colchicine to arrest the mitotic division.
3. A hypotonic solution is added to spread out the chromosomes.
4. Fixation is done by Carnoy’s solution.
5. Now put the cells on the slide.
6. Cell membranes are ruptured and chromosomes remain in well-defined groups.
7. Staining:
   1. The chromosomes are stained by various staining agents like Giemsa or Fluorescent material.
8. Karyotyping: Now select cells with intact chromosomes.
   1. Chromosomes are counted, identified, and evaluated.
   2. This is the arrangement and pairing of cell chromosomes, starting from the largest to the smallest in size.
9. Reporting: Count autosomal chromosomes and these are numbered according to their size.
   1. The larger one is labeled as 1.

Reporting of Chromosomal analysis:

1. Hyperploidy is an extra chromosome.
2. Hypoploidy when the chromosomes are missing.
3. Duplication when part of a chromosome is duplicated.

4. Deletion when the part of a chromosome is missing.

5. Addition when the chromosome has the additional material.
6. Insertion when the part of a chromosome is repositioned into a different area of the karyotype.
7. Inversion when the chromosome segment is reversed in the orientation.

8. Mosaic when some cells have abnormal cytogenetic abnormality whereas the other cells don’t have it.
9. Translocation when there is a balanced exchange of the chromosome without any loss or gain of the material.

Chromosomal abnormalities and syndromes:

Chromosomal abnormality	Disease or syndrome	Defect
Philadelphia	Chronic myelocytic leukemia
One X (45 X0)	Turner syndrome	sex chromosome is missing
Extra X in male (47 XXY)	Klinefelter syndrome	2 or more chromosome with one Y chromosome
Trisomy 21	Down syndrome	three copies of chromosome 21
5 p deletion	Cat Cry
trisomy 18	Edward’s syndrome
Trisomy 13	Patau syndrome
Mutation 11	Sickle cell anemia
Hyperploidy	In some acute lymphoblastic leukemia
Hypoploidy	In some myelodysplastic syndrome
Trisomy 8 mosaic	Trisomy 8 syndrome
Trisomy 22q 11-pter	Cat-eye syndrome
69, XXY	Triploidy
Xq27.3	Fragile X syndrome
47, XYY	XYY syndrome
47, XXX	Tripple X syndrome
Xq13-21.1 sex-linked	Severe combined immune deficiency (SICD)
Xp11-11.3	Wiskott-Aldrich syndrome
11q 22.3	Ataxia telangiectasia
X q222	X-linked agammaglobulinemia
6p21.3	Selective IgA deficiency

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