Karyotyping is a common clinical genetic technique to observe and investigate chromosomes. Scientists using the technique for a long time, though not less known.
The karyotyping technique is now common for prenatal testing, fetal chromosome testing and to rule out other pregnancy-related problems and chromosomal aberrations.
It is very important for couples who are going for karyotyping, to understand the procedure, purpose and results of karyotyping. So we think to write an article like the FAQ which cover the common question of patients related to karyotyping or a karyotype test.
Note that most of the points and answers will be explained non-technically so that the common person can understand.
What is karyotyping?
Put simply, it is a test often advice during pregnancy or to infertile couple to understand their chromosome structure and composition. It studies chromosomes, their structure and related disorders and hence is a type of genetic test.
A small amount of blood sample is taken from the patient or couple and sent for testing. Experts isolate chromosomes and study them.
You can read this article to learn more: What is karyotyping?
What are the characteristics of the human karyotype?
Here are the few important characteristics enlisted below,
- Human karyotypes are present in a pair
- 22 pairs are autosomes and a single pair of sex chromosomes are present in a karyotype.
- Every chromosome pair are different in structure and composition of genetic material.
- Chromosomes are stained with Giemsa
- Karyotype comprises two different regions, denser heterochromatin regions and lighter euchromatin regions.
- The euchromatin and heterochromatin regions are stained lighter and darker, respectively.
- Every chromosome is distinguished by its number, shape, size and position of the centromere.
- Based on the location of the centromere, the karyotype is classified into metacentric, submetacentric, acrocentric and telocentric.
- Depending upon the banding pattern, varied structural abnormalities can be studied.
Is there any karyotype analog to humans?
Every karyotype set is different, meaning, the structure and number of chromosomes vary among different organisms. Even the karyotype of two individuals isn’t exactly similar.
The genomic content vary from person to person and organism to organism therefore the number, structure and content of chromosome or karyotype vary as well. So technically, no karyotype exist which is analog to humans.
This shows that no two karyotypes in the world are similar, none of the karyotypes are analog to humans. Take a look at this table:
| Organism | Number of chromosomes | Pairs |
| Human | 46 | 23 |
| Puffer fish | 42 | 21 |
| dog | 78 | 39 |
| Sun flower | 34 | 17 |
| Cat | 38 | 19 |
| Pea plant | 14 | 7 |
Can a karyotype test be repeated? Can the results change?
The karyotype test can be repeated using the same sample type from a different sample (taken afterward), chromosome number and structure remain the same in all tissue or cell types, except germ cell and in case of mosaicism.
So as a couple, if you have done karyotype, you can repeat it. However, repeat sample collection isn’t advisable in the case of fetal samples like amniotic fluid or chorionic villi, as the risk of miscarriage is associated. If you wish to read more on the present topic, read this article:
When you repeat the karyotype test, the result still remains the same, until the performer has interpreted it wrongly.
For example, if the karyotype of your showing the translocation between chromosome 8 and 22, the same results will be observed when repeating to the same or other testing centers.
The number and structure of chromosomes remains same throughout the life of an organism or person. Although some external factor may damage the chromosome structure afterward.
Are chromosomal abnormalities permanent or temporary?
Clearly, the chromosomal abnormalities are permanent, when a fetus recieves abrrent chromosome, he or she have to live with it throughout their life. But by taking some preventive action, therapy and medication, it can be managed.
Chromosomal abnormality is permanet and can’t be repaired.
What a karyotype can’t detect?
It is also important for you as patient to know, what a karyotype can’t detect. Usually numerical abnormalities are detected but structural aberrations are hard to find.
Still some of the known structural aberrations can be detected.
Minor deletion, duplication and translocation can’e be detected using karyotyping. In addition, mutations at DNA or gene level can also not be detected.
Conclusive, a karyotype test can’t detect DNA mutations, gene mutation, and smaller copy number variations.
Can a baby suffer from a genetic disorder even after a normal karyotype and FISH test?
Yes. as we explained in the above section, the karyotype test and FISH can detect structural and numerical chromosomal abnormalities only on a large scale.
Even smaller copy number variations less than 100Kb can’t be detected using either technique. These chromosome aberrations can be detected;
- Trisomy- Down syndrome, Edward syndrom, Patau syndrome.
- Monosomy- cry-du-chat syndrome and turner syndrome
- Sex chromosome abnroamlity- Klinefeter and XYY syndrome.
- Certain carcinoma and sarcoma.
But other genetic abnormalities which are related to gene or DNA mutation can’t be detected using either technique. So even though your fetus’ karyotype or FISH test is normal, it may have other genetic abnormalities as well.
But don’t be panic, go for gene or DNA testing if your doctor advice.
If a parent’s karyotype is normal, what is a possibility of chromosome abnormality in a baby like 18p deletion?
If a parent’s karyotype is normal, still there is a 100% chance that the baby may have any chromosome or karyotyping abnormality. In most cases the 18p deletion is non-inherited. This means, chromosomal abnormalities such as 18p deletion, arise de novo– it occurs sporadically.
Wrapping up:
Karyotyping is one of the best technique to date to study chromosomes, especially in the case of fetal testing or prenatal screening. But there are some limitations make it difficult to use.
Every karyotype should have been done immediately, as time passes cells viability decreases. moreover, the performer and evaluator should have enough experience to perform and interpret results. The entire process is also manual and need continuous optimization to achieve maximum good results.