Comparison of sperm morphology and nuclear sperm quality in SPATA16- and DPY19L2-mutated globozoospermic patients

The aim of this study was to compare the sperm morphology and nuclear sperm quality (sperm aneuploidy and DNA fragmentation) in two groups of globozoospermic patients: DPY19L2-mutated patients (n = 6) and SPATA16-mutated patients (n = 2). Results for these two groups were also compared to a group of fertile men (n = 25). Fluorescence in situ hybridisation was performed for chromosomes X, Y and 18. Sperm DNA fragmentation was evaluated by TUNEL assay. Sanger sequencing was performed for mutations screening of DPY19L2 and SPATA16 genes. Sperm analysis revealed a classic phenotype of total globozoospermia in DPY19L2-mutated group and a particular phenotype characterised by a predominance of double/multiple round-headed (39.00 ± 4.2%) and multi-tailed spermatozoa (26.00 ± 16.97%) in SPATA16-mutated group. FISH analysis showed a significantly higher aneuploidy rate in globozoospermic patients compared to controls (p < 0.05), and a higher rate was observed in SPATA16-mutated group compared to DPY19L2-mutated group (p < 0.05). DNA fragmentation index was significantly higher in globozoospermic men compared to controls (p < 0.001), and there is no statistically significant difference between the two globozoospermic groups. We showed that SPATA16 defects could be associated with an abnormal meiosis leading to a particular morphological sperm defect of double/multiple round-headed and multi-flagella and a higher sperm aneuploidy rate than in case of DPY19L2-defects in classic globozoospermia.

A new mutation identified in SPATA16 in two globozoospermic patients

PURPOSE

The aim of this study is to identify potential genes involved in human globozoopsermia.

METHODS

Nineteen globozoospermic patients (previously screened for DPY19L2 mutations with no causative mutation) were recruited in this study and screened for mutations in genes implicated in human globozoospermia SPATA16 and PICK1. Using the candidate gene approach and the determination of Spata16 partners by Glutathione S-transferase (GST) pull-down four genes were also selected and screened for mutations.

RESULTS

We identified a novel mutation of SPATA16: deletion of 22.6 Kb encompassing the first coding exon in two unrelated Tunisian patients who presented the same deletion breakpoints. The two patients shared the same haplotype, suggesting a possible ancestral founder effect for this new deletion. Four genes were selected using the candidate gene approach and the GST pull-down (GOPC, PICK1, AGFG1 and IRGC) and were screened for mutation, but no variation was identified.

CONCLUSIONS

The present study confirms the pathogenicity of the SPATA16 mutations. The fact that no variation was detected in the coding sequence of AFGF1, GOPC, PICK1 and IRGC does not mean that they are not involved in human globozoospermia. A larger globozoospermic cohort must be studied in order to accelerate the process of identifying new genes involved in such phenotypes. Until sufficient numbers of patients have been screened, AFGF1, GOPC, PICK1 and IRGC should still be considered as candidate genes.

Identification of a new DPY19L2 mutation and a better definition of DPY19L2 deletion breakpoints leading to globozoospermia

STUDY HYPOTHESIS

The purpose of this study was to analyze DPY19L2 sequence variants to investigate the mechanism leading to the entire DPY19L2 deletion in a large cohort of infertile globozoospermic patients.

STUDY FINDING

An improved analysis of the DPY19L2 deletion breakpoints (BPs) allowed us to identify two BPs located in a small 1 kb region and to more precisely localize the BPs reported previously.

WHAT IS KNOWN ALREADY

Three genes [spermatogenesis associated 16 (SPATA16), protein interacting with PRKCA (PICK1) and DPY19L2] were previously correlated with globozoospermia, but a homozygous deletion of the entire DPY19L2 was identified as the most frequent alteration causing this phenotype. In addition, several point mutations in this gene were reported. In previous work, we have identified nine BPs for the DPY19L2 deletion clustered in two hotspot regions, while others reported a total of five BPs.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

We screened for the DPY19L2 deletion and for mutations in the DPY19L2, SPATA16 and PICK1 genes in a cohort of 21 Tunisian globozoospermic patients. In order to characterize the DPY19L2 deletion BPs, we sequenced a 2 kb fragment on low copy repeat (LCR) 1 and LCR2 in Tunisian fertile controls to distinguish between single-nucleotide polymorphisms (SNPs) and LCR-specific markers.

MAIN RESULTS AND THE ROLE OF CHANCE

Molecular analyses performed on 18 genetically independent individuals showed that 11 (61.1%) were homozygous for the DPY19L2 deletion, 2 (11.1%) were homozygous for the non-synonymous mutation (p.R298C) in exon 8, 1 patient (5.6%) was homozygous for a new splice-site mutation at the junction exon-intron 16 [c.1579_1580+4delAGGTAAinsTCAT] and no DPY19L2, SPATA16 or PICK1 mutations were identified for 4 patients (22.2%). By defining 15 specific LCR markers, we characterized 2 BPs for the DPY19L2 deletion in 11 patients showing the homozygous deletion. Using 20 non-LCR-specific SNPs, we identified 8 distinct haplotypes.

LIMITATIONS, REASONS FOR CAUTION

A limitation of this study is the small number of patients owing to the rarity of this form of male infertility.

WIDER IMPLICATIONS OF THE FINDINGS

Our data showed that some nucleotides, described by others as LCR-specific markers and used to limit their BPs, were in fact SNPs demonstrating the difficulty in precisely determining the localization of BPs.

LARGE SCALE DATA

Not applicable.

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by the French Centre National de la Recherche Scientifique (CNRS), Institut National de la Santé et de la Recherche Médicale (INSERM), the Ministère de l'Education Nationale et de l'Enseignement Supérieur et de la Recherche, the University of Strasbourg, the University Hospital of Strasbourg, the Agence Nationale pour la Recherche, the Agence de la BioMédecine and l'Agence Universitaire de la Francophonie (AUF). There are no conflicts of interest to declare.