Genetic causes of male infertility

No association found between gr/gr deletions and infertility in Brazilian males

The Y chromosome carries several spermatogenesis genes distributed in three regions: AZFa, AZFb and AZFc. Microdeletions in these regions have been seen in 10% of sterile males with azoospermia or oligozoospermia, the most frequent of them being characterized by a complete deletion of AZFc region. A partial AZFc deletion named gr/gr has been singled out as a risk factor for spermatogenic failure. However, other authors have diagnosed it as a polymorphic deletion with no clinical relevance. We decided to investigate the association of gr/gr deletion and infertility in Brazilian males. We analysed 350 individuals (110 azoospermic, 122 fertile and 118 presumably fertile) and observed 12 g/gr deletions: five in infertile men (4.5%), three among fertile males (2.5%) and four in probably fertile individuals (3.4%). These differences were not statistically significant. Then, we decided to ascertain whether the clinical impact of the gr/gr deletion was associated with the type of Y chromosome. We have identified Y-chromosome haplogroups using 22 unique event polymorphisms (UEPs). Among the individuals with the gr/gr deletion, we found haplogroups R, K*, F*, E1, E3b2 and E3b*, all of which are common in white Brazilian males, and none revealed a particular association with infertility. Taken together, these results show no evidence of association between the occurrence of gr/gr deletion and male infertility.

Intracytoplasmic injection of spermatozoa and spermatogenic cells: its biology and applications in humans and animals

Intracytoplasmic sperm injection (ICSI) has become the method of choice to overcome male infertility when all other forms of assisted fertilization have failed. Animals in which ICSI has produced normal offspring include many species. Success rate with normal spermatozoa is well above 50% in the mouse but ICSI success rates in other animals have been low, ranging from 0.3 to 16.5%. Mouse ICSI revealed that spermatozoa that cannot participate in normal fertilization can produce normal offspring by ICSI, provided their nuclei are genomically intact. Human ICSI using infertile spermatozoa has been highly successful perhaps because of the intrinsic instability of human sperm plasma membrane. The health of children born after ICSI and other assisted fertilization techniques is of major concern. Careful analyses suggest that higher incidences of congenital malformations and/or low birth weights after assisted fertilization are largely attributable to parental genetic background and increased incidence of multiple births, rather than to the techniques of assisted fertilization. Since the physiological and nutritional environments of developing embryos may cause persisting alteration in DNA methylation, extreme caution must be exercised in handling gametes and embryos in vitro. In the mouse, round spermatid injection (ROSI) has been routinely successful but its use in humans is controversial. Whether human ROSI and assisted fertilization involving younger spermatogenic cells are medically safe must be the subject of further investigations.

Production of fertile offspring from genetically infertile male mice

A number of recessive autosomal genes cause male infertility. Male mice homozygous for the blind-sterile (bs/bs) and quaking-sterile (qk/qk) gene mutations are sterile, because they either do not produce any spermatozoa or produce only a few abnormal spermatozoa. Mice lacking the cyclic AMP responsive-element modulator gene are sterile due to failure of spermiogenesis. All these mice, however, are able to produce fertile offspring when their spermatozoa or round spermatids are injected into oocytes of normal females. This implies that genetic and epigenetic elements necessary for syngamy and embryonic development are established in round spermatids and spermatozoa of these animals, even though their spermatogenic cells are destined to die (bs/bs and qk/qk) or are programmed to undergo apoptosis (cyclic AMP responsive-element modulator-null) without becoming functional spermatozoa.

Duplication 4p and deletion 4p (Wolf-Hirschhorn syndrome) due to complementary gametes from a 3:1 segregation of a maternal balanced t(4;13)(p16;q11) translocation

We present clinical and cytogenetic data on a family with a t(4;13)(p16;q11) translocation present in four generations. The balanced translocation resulted in one individual with monosomy 4p and one individual with trisomy 4p, due to 3:1 segregation. The male patient with trisomy 4p was fertile and transmitted the extra chromosome to his daughter.

Chimerism in a fertile woman with 46,XY karyotype and female phenotype

We report on the unexpected finding of a 46,XY karyotype in a 30 year-old woman with normal ovarian function and a former pregnancy at 17 years of age. Chromosome analysis was performed prior to intracyoplasmic sperm injection (ICSI), due to infertility of her husband. Repeated chromosome analysis in lymphocytes of the female resulted in a normal male karyotype. Fluorescence in-situ hybridization (FISH) analysis of cultured lymphocyte interphase nuclei detected in 99% of the cells one X and one Y chromosome-specific signal respectively, whereas two X chromosome-specific signals were observed in only 1% of the nuclei. Chromosome analysis of fibroblasts of ovarian and muscular tissues as well as of skin revealed a normal female karyotype (46,XX). Chimerism could be proven by variable number of tandem repeats (VNTR) analysis. Since the case history of the patient revealed that her twin brother died shortly after birth, it can be assumed that chimerism is caused by feto-fetal transfusion during pregnancy and delivery of the proposita.