YchromStrip kit is a test based on the reverse hybridization principle and that allows for the detection of deletions in the azoospermia factor (AZF), located on chromosome Y. These deletions are the cause of male infertility due to azoospermia (absence of sperms) or oligospermia (low sperm count).
Infertility is today a major health problem, affecting about 10-20% of couples. In particular, male factor is responsible for 30-50% of cases and, of these, 10 to 20% are attributed to azoospermia or oligospermia.
The study of Y microdeletions has become a routine diagnostic technique for infertile patients, because published studies suggest that they are one of the most common specific causes of male infertility. Furthermore, its diagnosis is key because carrier subjects are refractory to any treatment (ICSI is the only alternative), and because the resulting children will inherit these deletions.
YchromStrip test detects the presence or absence of 6 STSs (sequence tagged sites), located in three different regions of the Azoospermia factor: AZFa (sY84 and sY86), AZFb (sY127 and sY134) and AZFc (sY254 abd sY255). It also allows to verify the presence of sequences of three genes: ZFY (“Zinc Finger Y region”), ZFX (“Zinc Finger X region”) and SRY (“Sex reverse Y”).
Detection of major microdeletions recommended by EMQN
Use of SRY and ZFX/ZFY genes as internal controls
Automated reading with scanner available
Possibility to automate the hybridization process
The EMQN guidelines suggest a dual approach with a basic and an extension analysis for the diagnosis of the Y chromosome deletions. Kits with excessively high number of markers do not improve the sensitivity of the test, may even complicate the interpretation of the results and are not recommended. The basic analysis includes the use of the markers included in the YChromStrip product (sY84 and sY86 in the AZFa region, sY127 and sY134 in the AZFb region, and sY254 and sY255 in the AZFc region). When a deletion is observed, an extension analysis is suggested to better fine-tune the extent of the deletion. This extension analysis will also serve as an extra confirmation for the presence of the deletion. According to the EMQN guidelines, the extension analysis of the AZFb region should include STSs sY105 and sY121 or sY1224 at the proximal border, and sY143 or sY1192 and sY153 at the distal border. Thus, the YChromStrip test is a good alternative to perform the basic test, as a screening, as it can be used automatically and thus can be used to analyzed a high amount of samples. Later, the customer can analyze the samples with deletions with the home brew test, to have more info about the deletions, if it is needed.
The band corresponding to the SRY gene will always be present in the case of samples from subjects with male phenotype (subjects with karyotype 46XY, 47XXY, 47XYY, but also 46 XX positive for SRY gene), and absent in the case of typical female phenotypes. Some males might obtained this result, associated with a lack of Y Chromosome or, at least, with a lack of parts of it (deletion). A specialist should perform a cariotype of this patient to know exactly the genotype.
ZFY (Zinc Finger Y region) and ZFX (Zinc Finger X region) are two highly homologous genes located on chromosome Y and chromosome X, respectively, that are included to confirm the presence of DNA and that a proper amplification of the sample has occurred. The band corresponding to the genes ZFX and ZFY should always be present, regardless of whether the sample comes from a man or a woman. So if the extraction and the PCR are ok, this line should always appear
The SRY control gene used in the test is in the YP11.3 region, so if the gene is not detected it could be due to a deletion in that region, but not in others.