Human olfactory sensitivity for bourgeonal and male infertility: a preliminary investigation.

Olfactory receptor (OR) expression is also present in the sperm cells and could mediate sperm chemotaxis. OR1D2 was the first OR expressed in the testis demonstrated to be involved in chemotaxis and to be expressed also in the nose with a similar behavior. Bourgeonal is the OR1D2 most potent known agonist. Infertility affects ~15 % of couples in western countries and sometimes it is unexplained. This pilot study compared the bourgeonal olfactory thresholds, the ability of sperm to sense the bourgeonal and the frequency of 13 single nucleotide polymorphisms (SNPs) of OR1D2 gene in nine males suffering of unexplained infertility with a control group of 15 healthy males. The mean olfactory threshold for bourgeonal was statistically different between the study group (10.5 ± 3.7; median 12.3) and the control group (14.0 ± 2.8; median 15.5) (p = 0.006). Statistical analysis showed a significantly higher percentage of spermatozoa that migrated toward the capillaries filled with bourgeonal in the control group compared to the study group (p < 0.0001). Sperm migration was equally inhibited in both groups of subjects when, together with bourgeonal, capillaries were filled with undecanal, a strong bourgeonal inhibitor (p = 0.42). The 13 SNPs of OR1D2 revealed a statistically significant difference for allele and genotype frequency of rs769423 in study group versus control group (p = 0.02). The present preliminary study seems to confirm the important role of OR1D2 both in nose and spermatozoa and may explain the idiopathic infertility of the study group. Further studies on larger series are mandatory to confirm our preliminary evidence.