Sequencing of Sperm RNA May Improve Diagnosis of Male Infertility

Male factors can contribute to infertility in couples even when standard semen parameters are normal. Next-generation sequencing (NGS) of spermatozoal RNAs can provide a more comprehensive assessment of paternal contribution to fertility issues and may help guide choice of reproductive treatment, according to a study published July 8 in Science Translational Medicine. Development is underway for a prognostic assay that can predict birth outcome and the likelihood of success associated with different fertility treatments based upon the presence of certain RNA elements in sperm.

“Upon validation, this discovery may help to identify those couples who may benefit from assisted reproductive technologies [ARTs] and those couples who may be successful with minimal intervention,” said senior author Stephen Krawetz Ph.D., from Wayne State University (Detroit), in a statement. “It is our goal to use this technology to reduce both the time to live birth of a healthy child and the cost when couples seek infertility treatment, so as to reduce the stress on the couple.

According to the American Society for Reproductive Medicine infertility is a common problem, affecting at least 10 percent of all couples trying to conceive. More than one factor is responsible for infertility in more than 25 percent of infertile couples, but male evaluation is generally less thorough than for females. Currently, visual assessment of semen parameters (volume, sperm concentration, sperm motility, and sperm morphology) is used to identify male infertility due to “gross deficiencies,” but is ineffective for identifying male causes of infertility when sperm are morphologically normal. The large number of unique sperm transcripts revealed by RNA sequencing, experts say, suggests sperm has a role in influencing fertilization, early embryogenesis, and the offspring phenotype.

The current study assessed spermatozoal RNAs from 96 couples presenting with idiopathic infertility (infertility unexplained by standard procedures as confirmed by a reproductive endocrinologist and andrologist). Final reproductive outcome was used to evaluate sperm RNA elements (SREs) reflective of fecundity status. The 72 samples that passed all sequence quality measures were divided into three groups for analysis: group I, the positive control population, was used to determine the required SREs for live birth associated with “natural conception” (couples that achieved an LB through timed intercourse [TIC] during the first monitored cycle); group II test samples were composed of 55 couples, with the majority initially treated by intrauterine insemination [IUI] or TIC and the remainder deciding to undergo ART after semen assessment; and group III test samples included couples from an independent fertility clinic plus four couples with likely female infertility factor.

The researchers found a total of 648 SREs required for natural conception (defined as ranking above the 99th percentile rank and present at a constant level in the control group). Nine of these 648 SREs corresponded to intergenic regions, 12 to sperm-specific intronic elements; 42 within 24 different noncoding RNAs, all of which are likely regulatory, but most (585) were within exonic regions of 262 genes. Forty percent of these exonic region SREs were ontologically classified as associated with spermatogenesis, sperm physiology, fertility, and early embryogenesis before implantation. Patients with all SREs were significantly more likely to achieve live birth by TIC or IUI, compared to those men with one or more SRE(s) absent. The absence of the required SREs reduced the probability of achieving live birth by IUI or TIC from 73 percent to 27 percent. About 30 percent of the idiopathic infertile couples presented with an incomplete set of required SREs, suggesting a male component as the cause of their infertility.

“Absence of required RNA elements in sperm correlates with infertility but can be overcome with assisted reproductive technologies [in vitro fertilization],” the authors write. “As part of the clinical assessment, the absence of an SRE may suggest the earlier use of ART that could reduce the time to achieve live birth compared to current practice.”

The study was partially funded by EMD Serono (a division of Merck), which is currently in talks to license the test from Wayne State, Krawetz tells DTET.

Takeaway: RNA sequencing may be able to improve the non-morphological assessment of male infertility. With further validation, a comprehensive panel of SREs may be able to steer idiopathic infertile couples to the least invasive and least costly fertility treatment with the highest likelihood of success.