Chromosomal analysis (Karyotyping)-constitutional

Karyotyping is a laboratory test that is used in diagnosis of various chromosomal abnormalities. It is a type of cytogenetic test. A cytogenetic test is a lab test which helps to study chromosomes and their structure, variation and function. Humans have total of 46 chromosomes (23 pairs) in each cell with one pair inherited from mother and another from father .These chromosomes are made up of genes which are the basic unit of inheritance from parents to children. The total number of genes that a human has is called as genome. Genes are made up of DNA (deoxyribonucleic acid) molecules. These chromosomes carry all information for each cell to work efficiently.

The three main types of cytogenetic test are as follows:

• Karyotyping
• Fluorescent in situ hybridisation (FISH)-
• Comparative genomic hybridisation (CGH) and array comparative genomic hybridisation (aCGH).

Constitutional Karyotyping for chromosomal analysis helps to detect genetic abnormalities in children, adults, foetus during pregnancy and also to find the cause of foetal loss. These genetic abnormalities can either be inherited or can occur spontaneously. The common chromosomal abnormalities which can be detected with help of Karyotyping are as follows:

• Aneuploidies-presence of abnormal number of chromosomes .For example: down’s syndrome, patau syndrome, turner syndrome, Edward syndrome, klinefelter syndrome
• Polyploidy-presence of more than one pair of chromosomes like triploidy and tetraploidy
• Structural abnormalities-it is defined as breaking and rejoining of chromosomes or its segments .For example:deletions,duplications,insertions,translocations,inversions

The advantages of Karyotyping for chromosomal analysis are:

• It has genome –wide approach
• It can detect both numerical and structural chromosomal abnormalities
• It is an old and well established technology

Why is Chromosomal analysis (Karyotyping)-constitutional prescribed?

The health care provider may prescribe Karyotyping test in the following conditions:

1. during PREGNANCY-to detect foetal chromosomal abnormalities under certain circumstances like:

• abnormal maternal serum screening test(during first and second trimester)
• abnormal non-invasive prenatal testing(NIPT),screening(NIPS) OR abnormal cell-free DNA testing(cfDNA)
• maternal age >35 years
• family history of chromosomal abnormality

2. Fetal or neonatal death-to rule out genetic cause

3. Infant and childhood –to detect chromosomal abnormalities under certain circumstances like:

• Presence of birth defects, malformations, dysmorphism etc. in newborn
• presence of delayed growth, failure to thrive and short stature in child
• presence of development delay in child
• intellectual and learning disability in child
• presence of neurological symptoms like seizures, hypotonia in child
• presence of behavioural issues in child like autism, obsessive compulsive disorder, psychiatric illness

4. Adolescent and adult-in certain circumstances like:

• amenorrhea (absence of menses in females),premature ovarian failure, premature menopause
• azoospermia (absence of sperms ),oligospermia (decrease number of sperms)
• presence of recurrent abortions in female
• past history of birth of child with chromosomal abnormality

Procedure and prerequisites

The sample to be collected for Karyotyping test depends on the purpose of the test. The various samples on which Karyotyping test is done are as follows:

• peripheral blood
• buccal swab
• skin biopsy
• amniotic fluid
• chorionic villus sampling
• foetal tissues

Relevant clinical history/physical examination findings must be sent along with the sample. A properly filled requisition form must accompany the sample.