Molecular Test Detection

Test : Chromosome analysis


Indications : The test is ordered to -

• Determine if genetic factors are causing intellectual impairment, miscarriage, still birth, infertility, ambiguous genitalia
• Confirm the diagnosis of, or rule out, established chromosomal syndromes
• Diagnose malignancies and help in their treatment

When blood is used as the sample, one ml of peripheral blood is drawn intravenously from the candidate. The blood is cultured in the presence of a mitogen to bring about cell division. The cell division is then arrested in metaphase. The cells are later treated with hypotonic solution which causes the cells to burst. The nuclei are then mounted on a glass slide, stained and studied under a microscope. Photographs are taken to study the arrangement of chromosomes.

Physiology : Chromosome analysis, also known as karyotyping, is the examination of chromosomes in the blood or other tissues like the bone marrow.

This procedure is usually done to detect structural aberrations of the chromosomes, including deletions, duplications, translocations and inversions, that may be associated with several clinical conditions such infertility, stillbirth, miscarriage, birth defects, intellectual and developmental impairments and even malignancies.

Conventional karyotyping has its limitations in that it can only help in the analysis of structural aberrations in the larger chromosomes and not so much in the smaller ones. This limitation can be overcome with the use of more advanced techniques, such as FISH, which use molecular DNA probes.

However, the advantage associated with the conventional method is that it can be used to detect a range of structural abnormality, while FISH requires a prior knowledge of the abnormality at the time of testing.

Interpretation :

Normal

• Females: 44 autosomes and 2 sex chromosomes (XX), reported as 46, XX
• Males: 44 autosomes and 2 sex chromosomes (XY), reported as 46, XY

Abnormal

Any deviation from normal result could indicate an abnormality due to a genetic syndrome or condition, such as:

• Down syndrome- 47xy, +21
• Klinefelter syndrome- 47xxy
• Trisomy 18
• Turner syndrome - 45 X0
• Philadelphia chromosome - 9:22 translocation

There can be many other conditions too that are not listed above.

Sample : Interpretation is provided with the report

Test Method : Lymphocyte culture

Related Tests : Whole blood, bone marrow

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