Study question: What are the relationships between telomere lengths in leukocytes and sperm, sperm count and parents' age at conception in a group of apparently healthy subjects of the same age?
Summary answer: Sperm telomere length (STL) is related to sperm count, it is lower in oligozoospermic than in normozoospermic men and it is directly related to parents' age at conception.
What is known already: Leukocyte telomere length (LTL) decreases with age but STL increases and offspring of older fathers tend to have longer leukocyte telomeres. Only one study analyzed STL in relation to male fertility, and reported shorter telomeres in infertile versus fertile men. No data have been reported on STL in relation to parents' age at conception.
Study design, size, duration: Prospective study conducted from January to December 2012 of 18-19-year-old high school students.
Participants/materials, setting and methods: The volunteers were 81 apparently healthy subjects, including 61 with normozoospermia and 20 with idiopathic oligozoospermia. Leukocyte and sperm telomere length were measured by real-time PCR. Data were analyzed for determining the relationships between LTL, STL, sperm count and parents' age at conception.
Main results and the role of chance: Sperm and leukocyte telomere length were strongly correlated, but STL was significantly longer. A significant positive correlation between STL and total sperm number was found. STL was significantly lower in oligozoospermic than in normozoospermic men. Finally, we found a significant positive relationship between maternal age and both leukocyte and sperm telomere length and a significant positive relation between paternal age and STL in the offspring. The relative contributions of mothers' and fathers' ages to their offspring's telomere length could not be determined because of the high correlation between paternal and maternal ages.
Limitations and reasons for caution: Although consistent with previous findings, this is the first study on telomere length in oligo- and normozoospermic men and included a relatively low number of subjects. Our study was also restricted to young (18-19 year old) men, so future studies should determine whether our findings can be generalized to men at ages typically encountered at fertility centers. Future studies should also try to determine the possible effect of abstinence time and frequency of ejaculation with STL.
Wider implications of the findings: Our study sheds new light on the association between STL and sperm count and on the inheritance of telomere length (in leukocytes and sperm) in relation to the parents' age at conception. Additional studies are needed to confirm these observations, to clarify if the association between shorter STL and damaged spermatogenesis represents a pathophysiological link, and to determine the effect on offspring telomere length of assisted reproduction techniques performed on couples of advanced age or where the man is oligozoospermic.
Study funding/competing interest(s): This work was supported by the Italian Ministry of University and Research (grant no. 2009AMPA9C to C.F.) and Padova University (grant 2010 to A.D.R.). The authors have no competing interests to declare.
Keywords: male infertility; oligozoospermia; paternal age at conception; spermatogenesis; telomere length.