What is the FISH test on spermatozoa?

Fish sperm test

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When faced with a possible fertilit problem, doctors often recommend a variety of tests to define the causes. FISH testing of sperm is one of these, especially when assisted reproductive treatments do not seem to solve the problem. We know how complex this can be for any person and, in this situation, we recommend first and foremost to have the necessary information.

FISH in spermatozoa allows the detection of numerical alterations in the chromosomes that cause the most frequent reproductive aneuploidies. Read on to find out more about the features of this test.

FISH test on sperm: what is it?

Fluorescent in situ hybridisation is called FISH. It is a useful cytogenetic technique to study aneuploidy and structural rearrangements in all cell types. In this case, the technique is performed on the nuclei of male gametes in semen samples. Through the use of specific fluorescent probes for certain chromosomes, the number of chromosomes present can be determined.

This test aims to evaluate the number of certain chromosomes (usually 13, 18, 21, X and Y) in the semen in order to estimate the proportion of abnormal spermatozoa and assess the patient’s reproductive risk.

Many medical papers and articles refer to the FISH study and many other publications also point out how the results should be evaluated in order to make the best use of them.

How are sperm produced?

The process by which spermatozoa are produced is spermatogenesis. It takes place inside the testicles, within rounded structures called seminiferous tubules. This process occurs continuously in adult men. The complete cycle of spermatogenesis requires 75-90 days in the human species.

Spermatozoa are the male sex cells, the male gametes. They are haploid cells, which means that they possess half of the chromosomal endowment of the species. The process of spermatogenesis must change from somatic cells with 46 chromosomes (diploid) to sex cells with 23 chromosomes (haploid) through meiosis. This has a specific biological function: once fertilisation occurs and two gametes fuse, we will obtain a zygote with 46 chromosomes.
Once formed, the sperm are expelled into the centre of the tubule and transported to the epididymis (upper part of the testicle), where they undergo their final maturation.

What is the FISH technique in spermatozoa?

Let’s take a closer look at what this effective method of sperm detection is all about. This cytogenetic technique consists of applying certain specific DNA probes to certain chromosomal regions. The usual analysis evaluates chromosomes 13, 18, 21, X and Y, but there is the possibility to extend it to more chromosomes. The aim of this technique is to detect the chromosomal endowment, i.e. how many copies of each chromosome are analysed in the spermatozoa. This reveals a result that may be pathological or normal.

Its objective is to verify that each of the spermatozoa possesses a single chromosome of each of the chromosomes studied, i.e. that the reproductive cell is unisomic for each of the chromosomes analysed in the FISH study.

How is it done?

As explained above, the FISH technique performs an indirect análisis of the chromosome content in the interphase nucleus of spermatozoa. This is achieved by working with a semen sample that must have been abstinent for at least two days prior to delivery to the laboratory for analysis.

From there, the procedure carried out by the laboratory consists of several stages:

Spermatozoa are fixed, a solution is prepared and spread on a slide.
Chromatin decondensation occurs because spermatozoa are small in size and the chromatin inside the nucleus is highly compacted. This substance, located in the nucleus of cells during interphase, is what forms the chromosomal material during metaphase and is composed of DNA and proteins.
Specific probes are used for each of the chromosomes to be studied: the most frequent are for chromosomes 13, 18, 21, X and Y, as these are the chromosomes associated with the most frequent foetal aneuploidies.

Sperm DNA is denatured by increasing the temperature (to over 70 degrees) to allow the probes to intercalate between the DNA strands when the temperature returns to normal.

The next step is the visualisation and interpretation of the hybridisation signals. This is done by using a fluorescence microscope. What is observed is whether there is a signal from a large number of spermatozoa because spermatozoa with only one signal for each chromosome being analysed will be considered normal.

When is it indicated?

FISH analysis of sperm is indicated in cases of repeated miscarriages or implantation failure. Its results, in the context of other tests and in conjunction with the clinical history, are very powerful.

Where to do it?

Let us start by pointing out that this type of test should always be carried out in the context of a follow-up with a health professional. Likewise, an experienced and certified laboratory is always the best choice.

At Ambar Lab we offer, manage and coordinate the performance of more than 3000 tests, all of which are included in our test catalogue. Our team believes in science as the answer to many of today’s unknowns and works to ensure that tests answer these questions, because we know that knowledge is the key to making our clients’ work easier.

We believe in the relationship with our client as a key factor in the patient’s wellbeing. Whether you are a hospital, a laboratory, a drug developer or a medical researcher, we can meet all your needs.
Our services range from performing laboratory diagnostic tests to collaborating in the development of new projects and advising on laboratory management issues, so if you do your testing with us, you are in the best hands.

Contact us to get advice from our team of experts and find out more about our services.

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