High frequency of DAZ1/DAZ2 gene deletions in patients with severe oligozoospermia.

Deletions of the DAZ gene family in distal Yq11 are always associated with deletions of the azoospermia factor c (AZFc) region, which we now estimate extends to 4.94 Mb. Because more Y gene families are located in this chromosomal region, and are expressed like the DAZ gene family only in the male germ line, the testicular pathology associated with complete AZFc deletions cannot predict the functional contribution of the DAZ gene family to human spermatogenesis. We therefore established a DAZ gene copy specific deletion analysis based on the DAZ-BAC sequences in GenBank. It includes the deletion analysis of eight DAZ-DNA PCR markers [six DAZ-single nucleotide varients (SNVs) and two DAZ-sequence tag sites (STS)] selected from the 5' to the 3'end of each DAZ gene and a deletion analysis of the gene copy specific EcoRV and TaqI restriction fragments identified in the internal repetitive DAZ gene regions (DYS1 locus). With these diagnostic tools, 63 DNA samples from men with idiopathic oligozoospermia and 107 DNA samples from men with proven fertility were analysed for the presence of the complete DAZ gene locus, encompassing the four DAZ gene copies. In five oligozoospermic patients, we found a DAZ-SNV/STS and DYS1/EcoRV and TaqI fragment deletion pattern indicative for deletion of the DAZ1 and DAZ2 gene copies; one of these deletions could be identified as a 'de-novo' deletion because it was absent in the DAZ locus of the patient's father. The same DAZ deletions were not found in any of the 107 fertile control samples. We therefore conclude that the deletion of the DAZ1/DAZ2 gene doublet in five out of our 63 oligozoospermic patients (8%) is responsible for the patients' reduced sperm numbers. It is most likely caused by intrachromosomal recombination events between two long repetitive sequence blocks (AZFc-Rep1) flanking the DAZ gene structures.

The shorter zinc finger protein ZNF230 gene message is transcribed in fertile male testes and may be related to human spermatogenesis.

The zinc finger gene family represents one of the largest in the mammalian genome, with several of these genes reported to be involved in spermatogenesis. A newly discovered gene has been identified that is expressed abundantly in the testicular tissue of fertile men as determined by mRNA differential display. The gene encodes a C(3)HC(4)-type zinc finger protein motif (ring finger motif) consistent with a role in pre-meiotic or post-meiotic sperm development. The gene was named ZNF230 and mapped to the short arm of chromosome 11 (11p15). ZNF230 has two transcripts, of 1 kb and 4.4 kb in length. The shorter 1 kb transcript was only detected in testicular tissue whereas the longer 4.4 kb transcript was not detected in testis but was found in several other tissues. The lack of detectable ZNF230 expression in azoospermic patients by reverse transcriptase-mediated PCR analysis is interpreted to mean that this gene is involved in maintaining normal human male fertility.

High deletion frequency of the complete AZFa sequence in men with Sertoli-cell-only syndrome.

We have developed a rapid screening protocol for deletion analysis of the complete AZFa sequence (i.e. 792 kb) on the Y chromosome of patients with idiopathic Sertoli-cell-only (SCO) syndrome. This Y deletion was mapped earlier in proximal Yq11 and first found in the Y chromosome of the SCO patient JOLAR, now designated as the AZFa reference patient. We now show that similar AZFa deletions occur with a frequency of 9% in the SCO patient group. In two multiplex polymerase chain reaction experiments, deletions of the complete AZFa sequence were identified by a typical deletion pattern of four new sequence-tagged sites (STS): AZFa-prox1, positive; AZFa-prox2, negative; AZFa-dist1, negative; AZFa-dist2, positive. The STS were established in the proximal and distal neighbourhoods of the two retroviral sequence blocks (HERV15yq1 and HERV15yq2) which encompass the break-point sites for AZFa deletions of the human Y chromosome. We have found deletions of the complete AZFa sequence always associated with a uniform SCO pattern on testicular biopsies. Patients with other testicular histologies as described in the literature and in this paper have only partial AZFa deletions. The current AZFa screening protocols can therefore be improved by analysing the extension of AZFa deletions. This may provide a valuable prognostic tool for infertility clinics performing testicular sperm extraction, as it would enable the exclusion of AZFa patients with a complete SCO syndrome.

Y-chromosomal DNA haplotypes in infertile European males carrying Y-microdeletions.

We have determined Y-chromosomal DNA haplotypes in 73 infertile European males carrying Y microdeletions and compared them with the haplotypes of 299 infertile males lacking microdeletions. Chromosomes were typed with a set of 11 binary Y markers, which identified 8 haplogroups in the sample. Haplogroup frequencies were compared between 3 microdeletion classes and the non-deleted infertile males. Deletions arise on many different haplotypic backgrounds. No statistically significant differences in frequency were seen, although the small number of AZFa deletions lay predominantly on one branch of the Y haplotype tree.

Two long homologous retroviral sequence blocks in proximal Yq11 cause AZFa microdeletions as a result of intrachromosomal recombination events.

We mapped the breakpoints of the AZoospermia factor a (AZFa) microdeletion located in proximal Yq11 in six men with complete germ cell aplasia, i.e. Sertoli Cell Only syndrome (SCO). The proximal breakpoints were identified in a long retroviral sequence block (HERV15yq1: 9747 nucleotides) at the 5' end of the DYS11 DNA locus in Yq11, interval D3. The distal breakpoints were found in a homologous HERV15 sequence block mapped to the Yq11 interval D6, i.e. in the distal part of the AZFa region (HERV15yq2: 9969 nucleotides). Compared with the HERV15yq1 sequence, HERV15yq2 is marked by a deletion of a HERV15 sequence domain at its 5' end and insertion of an LINE 1 3'-UTR sequence block (L1PA4) of similar length at its 3' end. The deletion of the L1PA4 element was recognized as the molecular origin of the DYS11 12f2 restriction fragment length polymorphism. For all six AZFa patients it was possible to perform PCR experiments bridging both retroviral sequence blocks, which map in a distance of 781.557 kb in proximal Yq11 in fertile men. The AZFa breakpoint-fusion regions were located in their recombined HERV15yq1/HERV15yq2 sequence blocks in either one of two long identical sequence domains (ID1 and ID2). We therefore assume that intrachromosomal recombination events between the two homologous retroviral sequence blocks in proximal Yq11 are probably the causative agents for most of the AZFa microdeletions observed in men with SCO syndrome. A mean value of 792 kb was estimated for their molecular lengths.