Sperm-FISH

Sperm-FISH

The treatment of infertility in men is still a challenge mainly due to the heterogeneity of the parameters involved in it. A man with a normal karyotype may carry chromosomal anomalies (aneuploidy) in his spermatozoa, as a result of errors occurring in the meiosis during spermatogenesis. It is worth mentioning that research has shown that high rates of aneuploidy in men’s sperm have a negative effect on pregnancy and often lead to spontaneous abortions of the first trimester.

One of the techniques used to examine aneuploidy in semen is fluorescent in situ hybridization (sperm FISH). The analysis involves the study of hundreds of spermatozoa using specific fluorescent probes for each of the following chromosomes: 13, 15, 16, 18, 21, 22, X and Y. The principle of the method is based on specific probes (DNA molecules) that bind to specific chromosomal regions. Each probe, because of complementarity, is linked to a single chromosome, indicating its existence.
The probe molecules are labeled with fluorochromes that give a signal (eg red or green) under the influence of light of appropriate radiation, thus making it easy to count them on the examined sample. Consequently, the method of the test is based on the fact that each light signal corresponds to a specific chromosome, allowing us to understand the absence or the addition of the chromosomes compared to normal. The results of the test are given as percentages of disomy (extra chromosome) and nullisomy (chromosome deficiency) and depend solely on the signals observed during the examination of the sample in the microscope.

The FISH examination of the semen is recommended in the following cases:

a. In men with normal and abnormal spermogram

b. In couples with recurrent miscarriages (>2)

c. In couples with more than 2 failed ICSI cycles

The test result reflects the percentage of spermatozoa in a semen sample, which show aneuploidy. Normal fertile men are considered to have sperm aneuploidy at a rate of 2-4%. Greater rates of aneuploidy are considered abnormal. Serious infertility cases have been found to be associated with chromosomal abnormalities greater than 27%. As the result of the test suggests, despite the presence of abnormal spermatozoa in a sample, there is still a proportion of normal ones, as well.

This examination is therefore a non-invasive tool that can provide answers regarding the couple’s infertility history and contribute to the decision on their treatment (eg pre-implantation testing).

The causes of a high rate of aneuploidy in semen are not yet completely known. However, some cases are associated with an increased abnormality rate during spermatogenesis. Such conditions can be detected in men who have received chemotherapy and/ or radiotherapy, in men of increased age and in men exposed to various toxic substances and/or radiation.

There is no specific treatment for the chromosomal abnormalities in sperm. However, in the above-mentioned cases, inhibition of the cause of aneuploidy may help reduce its rate. After a period of time after chemotherapy/ radiotherapy, the rate of aneuploidy in sperm can be reduced. At the same time, avoiding dangerous environmental factors and adopting a more careful and healthy lifestyle can contribute to the development of normal spermatozoa.