Compound heterozygous DMC1 variants cause non-obstructive azoospermia by defective replication protein A replacement.

Research Question: How does a compound heterozygous DMC1 variant, a meiosis-specific recombinase, affect homologous search and chain invasion during spermatocyte meiosis in a patient with non-obstructive azoospermia (NOA)?

Design: A patient with a compound heterozygous DMC1 variant associated with NOA was identified. Reverse transcription polymerase chain reaction and western blot were used to study the effect of this variant. Standard histological analysis and immunofluorescence staining investigated the patient's spermatogenic arrest. The accumulation of replication protein A (RPA), a single-stranded DNA-binding protein, was detected through immunofluorescence staining on chromosome spreads of spermatocytes. Dmc1 knockout (Dmc1) mice were constructed to replicate the results of chromosome spreads observed in the patient.

Results: The patient's compound heterozygous DMC1 variants (c.494+4A>G/c.597G>C) were associated with NOA. This patient showed nonsense-mediated mRNA decay of DMC1, significantly reducing DMC1 protein levels in germ cells. Spermatogenic arrest occurred during meiosis, with defects in chromosome pairing and DNA double-strand break repair. Dmc1 mice precisely replicated the human phenotype of defects in chromosome pairing and double-strand break repair. Further analysis revealed that, in the absence of DMC1, RPA (single-stranded DNA-binding protein) failed to be replaced by meiosis recombinase, leading to an accumulation in zygotene stage spermatocytes. This was confirmed by the Dmc1 knockout mouse model.

Conclusions: This novel compound heterozygous DMC1 variant disrupts germ cell meiosis and expands the known mutational spectrum of DMC1.