Distribution of MLH1 foci and inter-focal distances in spermatocytes of infertile men

In a previous study on severely infertile men, we observed alterations in the number of meiotic crossovers; however, it is unknown if these men also show alterations in the position of crossovers. Spermatocytes from 15 men (5 control men and 10 infertile men) were immunostained to observe the synaptonemal complex and MLH1 foci, which localize to sites of crossovers. Fluorescent in situ hybridization was performed to identify chromosomes 13, 18 and 21. Chromosome bivalents were separated into those with single and double crossover configurations, and the distribution of MLH1 foci along each chromosome arm was calculated. The inter-focal distances on chromosome 13 and 18 bivalents with double crossovers were also calculated. Four of the infertile men displayed an altered MLH1 distribution on at least one of the chromosome arms studied. Of these four men, two displayed reduced rates of meiotic recombination. Only one man displayed an abnormality in crossover interference, with inter-focal distances reduced on chromosome 13 bivalents. Recombination defects in infertile men may include alterations in the number of crossovers, the position of crossovers or both. Alterations in both the number and position of crossovers may increase the risk of aneuploid sperm in infertile men.