Objective: Telomerase is a ribonucleoprotein detectable in germ, stem and tumor cells. In male germ cells, it plays an essential role in transmitting full-length chromosomes to progeny, which is a prerequisite for male fertility. In our recent study, human telomerase reverse transcriptase (hTERT), a major component of the enzyme, was identified in testicular tissue as a highly specific marker of gametogenesis. The aim of this study was to determine whether quantification of hTERT mRNA expression can differentiate between various gametogenic disorders and thus predict the presence of haploid germ cells in testicular biopsies.Design: hTERT mRNA expression was quantified in 59 cryopreserved testicular tissue specimens by fluorescence real-time RT-PCR in a LightCycler®. The level of porphobilinogen deaminase (PBGD) mRNA in the tissue specimens was concomitantly determined as a reference for relative quantification. This was paralleled by conventional histological workup and wet preparation and, in selected cases, semithin sectioning preparation.Materials/Methods: Eighteen testicular biopsies were taken from patients with Sertoli-cell-only syndrome (SCOS), 19 from patients with maturation arrest (MA) (Johnsen Score 3-5) and 22 from patients who had obstructive azoospermia with normal spermiogenesis (OA) (Johnsen Score 6–10).Results: There were 130 (±23.8 standard deviation) mean hTERT mRNA copies normalized to 1000 copies of PBGD mRNA in tissue specimens with full spermatogenesis and 73 (±19.3) in those with MA, while only minimal hTERT expression (1.5 (±0.5) was detectable in SCOS specimens. hTERT mRNA expression was 89 (±12) in 5 SCOS specimens with focal islands of full spermatogenesis and 42 (±17) in 4 specimens with focal islands of spermatogenesis with maturation arrest.Conclusions: Our investigations show that the level of hTERT mRNA expression in testicular biopsies is correlated to specific stages of gametogenesis. Quantification of hTERT mRNA by fluorescence real-time RT-PCR is thus a highly sensitive and highly specific new technique that enables a new molecular-diagnostic subclassification of gametogenic disorders. It also opens up interesting perspectives in the assessment of testicular biopsies, particularly for detecting focal spermatogenesis in Sertoli-cell-only specimens.Supported by: University funding. Objective: Telomerase is a ribonucleoprotein detectable in germ, stem and tumor cells. In male germ cells, it plays an essential role in transmitting full-length chromosomes to progeny, which is a prerequisite for male fertility. In our recent study, human telomerase reverse transcriptase (hTERT), a major component of the enzyme, was identified in testicular tissue as a highly specific marker of gametogenesis. The aim of this study was to determine whether quantification of hTERT mRNA expression can differentiate between various gametogenic disorders and thus predict the presence of haploid germ cells in testicular biopsies. Design: hTERT mRNA expression was quantified in 59 cryopreserved testicular tissue specimens by fluorescence real-time RT-PCR in a LightCycler®. The level of porphobilinogen deaminase (PBGD) mRNA in the tissue specimens was concomitantly determined as a reference for relative quantification. This was paralleled by conventional histological workup and wet preparation and, in selected cases, semithin sectioning preparation. Materials/Methods: Eighteen testicular biopsies were taken from patients with Sertoli-cell-only syndrome (SCOS), 19 from patients with maturation arrest (MA) (Johnsen Score 3-5) and 22 from patients who had obstructive azoospermia with normal spermiogenesis (OA) (Johnsen Score 6–10). Results: There were 130 (±23.8 standard deviation) mean hTERT mRNA copies normalized to 1000 copies of PBGD mRNA in tissue specimens with full spermatogenesis and 73 (±19.3) in those with MA, while only minimal hTERT expression (1.5 (±0.5) was detectable in SCOS specimens. hTERT mRNA expression was 89 (±12) in 5 SCOS specimens with focal islands of full spermatogenesis and 42 (±17) in 4 specimens with focal islands of spermatogenesis with maturation arrest. Conclusions: Our investigations show that the level of hTERT mRNA expression in testicular biopsies is correlated to specific stages of gametogenesis. Quantification of hTERT mRNA by fluorescence real-time RT-PCR is thus a highly sensitive and highly specific new technique that enables a new molecular-diagnostic subclassification of gametogenic disorders. It also opens up interesting perspectives in the assessment of testicular biopsies, particularly for detecting focal spermatogenesis in Sertoli-cell-only specimens. Supported by: University funding.