What information does sperm diagnostics by the FISH method provide?

What information does

sperm diagnostics

by the FISH method provide?

FISH, or fluorescent in situ hybridization, is a method used to diagnose the genetic factors of male infertility. A standard sperm analysis (spermogram) offers only a partial understanding of a man’s fertility. It provides information about sperm count and quality characteristics (motility, morphology, agglutination, etc.). However, it does not reflect DNA integrity (sperm DNA fragmentation) or chromosomal composition.

A comprehensive evaluation of male factors in a couple’s infertility includes determining additional sperm characteristics.

Sperm diagnostics using the FISH method allows for an analysis of the chromosomal set in sperm cells and the identification of aneuploidies (an abnormal number of chromosomes in cells) using specific DNA-labeled fluorescent probes. Healthy sperm cells are haploid, meaning they carry half the full set of human chromosomes — 23 chromosomes, one from each pair. The gametogenesis process (formation of sex cells) is not 100% perfect, and a certain proportion of sex cells may have chromosomal abnormalities (aneuploidies). Issues arise when the level of aneuploidy is high.

The FISH sperm analysis panel includes sex chromosomes (X and Y) and autosomes (chromosomes 13, 18, and 21). This selection is based on the frequent identification of abnormalities in these locations. For example, sex chromosome abnormalities include Klinefelter syndrome (XXY) or Turner syndrome (X), while autosomal abnormalities like trisomies are associated with Patau syndrome (13), Edwards syndrome (18), and Down syndrome (21).

Based on medical indications, this analysis can be expanded to include other chromosomes if warranted by the patient’s medical history:

• Chromosomes 16 and 22 in cases of recurrent pregnancy loss.
• Chromosomes identified in abnormal karyotypes of the male partner.
• Chromosomes associated with karyotype abnormalities during previous pregnancies in the couple.

FISH analysis of sperm can help determine the proportion of sperm cells with chromosomal abnormalities and assess whether these exceed normal levels.

How is FISH sperm diagnostics performed?

The study uses a sperm sample from the patient, collected after a minimum abstinence period of 3 days. The FISH sperm analysis involves the following steps:

1. Fixation of sperm cells on a microscope slide.
2. DNA denaturation.

During the denaturation process, hydrogen bonds in the double-stranded DNA molecule are broken, transforming it into a single-stranded form. This allows fluorescently labeled DNA probes to hybridize (bind) to the target chromosomes.

3. Washing off excess probes and staining the sample to highlight sperm nuclei.
4. Visualization and interpretation of hybridization signals. The results are compared to values from a control population. Visualization is performed using a fluorescence microscope, allowing observation of the signals in many sperm cells. Normal sperm cells show one fluorescent signal for each analyzed chromosome.

What are the indications for sperm analysis using the FISH method?

The most common indications for FISH sperm diagnostics include:

• Older reproductive age (>40 years).
• Abnormal spermogram parameters.
• Pregnancy complications, such as miscarriage, fetal demise, or pregnancies with chromosomal abnormalities in the fetus.
• Repeated failed attempts at in vitro fertilization (IVF), including recurrent implantation failure (failure of the embryo to attach after embryo transfer).
• Male carriers of balanced chromosomal rearrangements (FISH analysis with individual probes to determine the ratio of normal/balanced and unbalanced sperm cells for the rearrangement).

Patients with an increased number of chromosomal abnormalities in their sperm, as determined by FISH analysis, are at higher risk of producing embryos with chromosomal abnormalities. This leads to reduced implantation potential, an increased risk of pregnancy loss, and a higher likelihood of having offspring with karyotype abnormalities.

If FISH sperm analysis reveals a significant increase in chromosomal abnormalities, preimplantation genetic testing for aneuploidy (PGT-A) is recommended, where medically appropriate for the couple. This testing allows for the selection of euploid embryos (with the correct number of chromosomes), increasing the likelihood of successful pregnancy and the birth of a healthy child.

Advantages and limitations of the FISH sperm diagnostics method

Advantages of FISH diagnostics:

1. Improved infertility treatment. Identifying chromosomal abnormalities in sperm allows reproductive specialists to make informed decisions about optimal infertility treatment methods, such as IVF with ICSI (intracytoplasmic sperm injection) and preimplantation genetic testing for aneuploidy (PGT-A).
2. Reduced genetic risks. FISH analysis results not only aid in infertility treatment but also provide information about the likelihood of passing chromosomal abnormalities to offspring.
3. Personalized treatment. FISH analysis results help create personalized treatment programs for couples facing infertility, recurrent miscarriages, or genetic disorders in their family.
4. Improved reproductive outcomes. Combining FISH diagnostics with modern technologies enables better selection of embryos with high viability and reduced risk of genetic abnormalities, positively impacting the likelihood of successful pregnancy.
5. Minimally invasive procedure. Unlike other genetic tests, FISH analysis does not require complex interventions and is performed directly on sperm cells collected in the sample.

Limitations:

1. Limited scope of analysis. The method evaluates only a specific number of sperm cells in the sample, so there is a risk of missing abnormalities in other cells.
2. Does not guarantee successful pregnancy. Even with normal FISH analysis results, other factors may affect the ability to conceive.

Interesting facts about FISH sperm diagnostics

• The name of the technology is metaphorical. FISH stands for Fluorescence In Situ Hybridization. It is nicknamed “fish” because the fluorescent probes “swim” and bind to specific chromosomes, producing bright light signals.
• Not limited to sperm analysis. While FISH is well-known for its use in reproductive medicine, it is also employed for tissue analysis, such as in cancer diagnostics and other genetic disorders.

FISH sperm analysis remains one of the most important tools in reproductive medicine and genetics due to its precision, speed, and efficacy, along with its wide range of applications.