Increased incidence of triplet repeat diseases expanded alleles in azoospermic men: a new concern for ICSI?

Abstract

Objective: Triplet repeat diseases (TRDs) are autosomal dominant neurodegenerative disorders, associated with abnormal expansion of polymorphic CAG/CTG, CGG/CCG or GAA/TTC motifs embedded within coding and non-coding regions of specific genes. A feature of TRDs is anticipation, whereby the disease severity increases and the age of onset decreases from one generation to the next due to genomic instability in meiotic cells. Some infertile patients present genomic instability. Several TRDs, like Kennedy Disease (KD) and Myotonic Dystrophy (MD) are characterized by decreased or abolished reproductive fitness; for others, this association has not been investigated, although animal models suggest this possibility. The objective of this study is to determine whether severe idiopathic male infertility patients exhibit meiotic instability with an increased incidence of TRD abnormal alleles. Design: A prospective controlled study of TRDs-associated loci repeat lengths in the somatic and germline tissues of non-obstructive azoospermic men. Men with obstructive azoospermia but normal histology served as controls. Statistical analysis was performed by a Cochran-Mantel-Haenszel test of differences between the severe infertile patients diagnosis (Sertoli cell only, maturation arrest, hypospermatogenesis) and the controls. Materials/Methods: DNA was extracted from paired blood and testis samples of 41 azoospermic patients and 20 controls and amplified by polymerase chain reaction for 6 loci associated with TRDs: KD, MD, Huntington Disease (HD) and Spinocerebellar Ataxia 1, 2 and 6 (SCA-1, SCA-2 and SCA-6, respectively). Triplet repeat lengths were determined by fragment analysis using an ABI 310 Analyzer and GeneScan software. Results: A significant increased incidence of total instability (94%) was observed between the paired blood and testis samples of Sertoli cell only (SCO) patients as compared to controls (p <0.08). When instability was present, repeat expansions were almost always observed in the patients testis, relative to their blood. Importantly, triplet repeat lengths above the minimum necessary to develop the TRD were observed in the somatic tissue of 5.3% of the SCO patients, but not the control group for the MD locus. Moreover, at the MD and SCA-2 loci, repeat lengths large enough to cause TRDs were observed in the testicular tissue of 15.8% and 5.3% of the SCO patients, as compared to 0% of the controls. Conclusions: SCO patients present a higher than normal incidence of genomic instability, with a propensity to repeat expansion in the testis at several TRDs loci. MD-associated alleles are present at a higher than normal frequency in the SCO patients. Thus, male infertility may be an early symptom of MD. A higher than expected percentage of patients seeking infertility evaluation may be mild-MD symptomatic carriers. A high percentage of expanded MD and SCA-2 alleles are present in the testis of SCO men. As all patients were candidates for testicular sperm extraction and ICSI, there is concern that the offspring conceived may be at increased risk for MD and SCA-2. Supported by: Supported in part by NIH P01HD 36289–01 (to DJL), Swiss National Science Foundation (to RC), Roche Research Foundation (to RC and DJL).