Association of azoospermia factor region deletions in infertile male subjects among Malaysians

Y-microdeletions: a review of the genetic basis for this common cause of male infertility

The human Y-chromosome contains genetic material responsible for normal testis development and spermatogenesis. The long arm (Yq) of the Y-chromosome has been found to be susceptible to self-recombination during spermatogenesis predisposing this area to deletions. The incidence of these deletions is estimated to be 1/4,000 in the general population but has been found to be much higher in infertile men. Currently, Y-microdeletions are the second most commonly identified genetic cause of male infertility after Klinefelter syndrome. This has led to testing for these deletions becoming standard practice in men with azoospermia and severe oligospermia. There are three commonly identified Y-microdeletions in infertile males, termed azoospermia factor (AZF) microdeletions AZFa, AZFb and AZFc. With increased understanding and investigation of this genetic basis for infertility a more comprehensive understanding of these deletions has evolved, with several other deletion subtypes being identified. Understanding the genetic basis and pathology behind these Y-microdeletions is essential for any clinician involved in reproductive medicine. In this review we discuss the genetic basis of Y-microdeletions, the various subtypes of deletions, and current technologies available for testing. Our understanding of this issue is evolving in many areas, and in this review we highlight future testing opportunities that may allow us to stratify men with Y-microdeletion associated infertility more accurately

AZFa Microdeletions: Occurrence in Chinese Infertile Men and Novel Deletions Revealed by Semiconductor Sequencing

OBJECTIVE

To evaluate the frequency of azoospermia factor (AZFa) microdeletions among infertile men and establish a new high-throughput sequencing method to detect novel deletion types.

MATERIALS AND METHODS

A total of 3731 infertile men were included. Karyotype analysis was performed using G-band staining of peripheral blood lymphocytes. Polymerase chain reaction (PCR) amplification using specific sequence-tagged sites (STS) was performed to screen for AZF region microdeletions of the Y chromosome. A novel semiconductor sequencing method was established to detect high-resolution AZFa microdeletions.

RESULTS

Of 3731 infertile men, 341 (9.14%) had microdeletions in AZFa, AZFb, or AZFc. Thirteen of these (3.81%) had a deletion in the AZFa region (mean age: 27.3 ± 4 years, range: 22-34), which included 12 subjects with a normal karyotype (46, XY) and 1 with Klinefelter syndrome (47, XXY). Four of 10 subjects with complete AZFa microdeletions (sY86 and sY84 loss) underwent semiconductor sequencing. They all had DNA sequence deletions from nt 14469266 to 15195932, whereas their fathers had no deletions. One subject with partial AZFa microdeletion (sY86 loss) and his father underwent semiconductor sequencing and STS-PCR analysis. The same deletion (sY86 loss with DNA sequence deletion from nt 14469266 to 14607672) was identified in both subjects. Forty sperm donators and 50 infertile men showed no AZFa microdeletions by either method.

CONCLUSION

AZFa deletions are present at a low frequency in men with azoospermia or oligozoospermia. Novel sequencing methods can be used for these patients to reveal high-resolution AZFa microdeletions.

Y chromosome azoospermia factor region microdeletions and transmission characteristics in azoospermic and severe oligozoospermic patients

Spermatogenesis is an essential reproductive process that is regulated by many Y chromosome specific genes. Most of these genes are located in a specific region known as the azoospermia factor region (AZF) in the long arm of the human Y chromosome. AZF microdeletions are recognized as the most frequent structural chromosomal abnormalities and are the major cause of male infertility. Assisted reproductive techniques (ART) such as intra-cytoplasmic sperm injection (ICSI) and testicular sperm extraction (TESE) can overcome natural fertilization barriers and help a proportion of infertile couples produce children; however, these techniques increase the transmission risk of genetic defects. AZF microdeletions and their associated phenotypes in infertile males have been extensively studied, and different AZF microdeletion types have been identified by sequence-tagged site polymerase chain reaction (STS-PCR), suspension array technology (SAT) and array-comparative genomic hybridization (aCGH); however, each of these approaches has limitations that need to be overcome. Even though the transmission of AZF microdeletions has been reported worldwide, arguments correlating ART and the incidence of AZF microdeletions and explaining the occurrence of de novo deletions and expansion have not been resolved. Using the newest findings in the field, this review presents a systematic update concerning progress in understanding the functions of AZF regions and their associated genes, AZF microdeletions and their phenotypes and novel approaches for screening AZF microdeletions. Moreover, the transmission characteristics of AZF microdeletions and the future direction of research in the field will be specifically discussed.