Sperm Aneuploidy Test. 5 chromosomes: 13, 18, 21, X and Y
1. What is the sperm aneuploidy test (SAT)?
The SAT is a genetic test that determines if there is an increased incidence of chromosome abnormalities in sperm. A normal sperm, like a normal egg, has 23 chromosomes. After fertilization, there are 46 chromosomes in total, and this number is important for the development of the baby. Embryos that have aneuploidy, or a numerical abnormality in the number of chromosomes, are not expected to be born healthy. Most of the time, aneuploidy in embryos is due to errors that occurred in the egg; however, some men have sperm with a higher incidence of chromosome abnormalities, and this can lead to aneuploidy in embryos. The SAT is a diagnostic test that can be helpful in cases of male-factor infertility.
The SAT analyzes 5 chromosomes whose anomalies can lead to miscarriages or live births with chromosomal abnormality syndromes including birth defects and mental retardation (chromosomes 13, 18, 21, X, and Y). Evaluation of these 5 chromosomes provides an indication of the likelihood of aneuploidy in sperm.
It is recommended in the following cases:
- Couples with repeated miscarriages.
- Couples with various assisted reproduction treatments without pregnancy.
- Men with normal chromosome pattern but generate chromosomally abnormal embryos.
- Men with azoospermia (< 1,000 000 sperm/mL)
Clinically, aneuploidy in the sperm has been associated with a lower pregnancy rate after ICSI, as well as a higher rate of miscarrige in couples with infertility. The consequences of aneuploidy in sperm will depend on the type of chromosome abnormality involved. Potential outcomes of aneuploidy include implantation failure, miscarriage, or the birth of a baby with birth defects and/or mental retardation. The most common syndromes caused by chromosome abnormalities are Patau syndromes, Edwards, Down, Klinefelter, Turner, XXX and XYY.
The SAT is a technique based on fluorescent in situ hybridization (FISH). FISH techniques involve using fluorescent probes that hybridize to the chromosomes being evaluated. The SAT uses probes for 5 chromosomes: 13, 18, 21, X and Y.
2. Who should do the SAT?
The SAT is indicated for couples who have an increased risk of chromosome abnormalities in offspring and where the man has male-factor infertility. The men themselves usually have normal chromosomes but the sperm production is abnormal. Other indications would be histories of repeat miscarriages of unknown cause, repeated implantation failure, and/or previous pregnancy with chromosomal abnormalities.
To obtain a clinically relevant result, we analyze 2,000 sperm for each chromosome, and the analysis is performed by two independent reviewers. The results are compared with laboratory internal controls.
3. What are the advantages of the SAT?
1. Can the SAT analyze other chromosomes?
Yes, when the SAT is requested because of a history of a previous pregnancy with chromosomal abnormality, the chromosomes involved in the abnormality can be analyzed.
2. Can SAT be performed in male carriers of structural chromosomal rearrangement?
Yes, a custom-designed protocol can be developed with fluorescent DNA probes directed to a specific rearrangement.
3. Should there be a period of sexual abstinence prior to sample collection?
Yes, men should abstain from sexual intercourse 2-3 days prior to sample collection.
4. Is there a minimum sperm count needed for the SAT?
No. In most cases, as long as sperm is observable in the sample being submitted, the SAT can be successfully performed. Only in rare cases will the number of sperm be insufficient.