Previously, reciprocal translocation between chromosome 17 and chromosome22 had been described in two male patients with reproductive problems of repeated spontaneous abortions in his wife (Table 1). Interestingly, the two involving chromosomes are characterized by the presence of chromosome-specific low copy repeats(LCR)(15)(16). The enrichment of LCR precipitated a high frequency of nonallelic homologous misalignments and unequal recombination during the meiosis, leading to the instabilities in the region of the chromosome 17 and chromosome 22. It is well known that, duplication of chromosome 17p11.2 results in Potocki-Lupski syndrome (PTLS), while its reciprocal deletion leads to Smith-Magenis syndrome (SMS)(17). In addition, alteration of gene dosage on part of 22q is responsible for the aetiology of a number of human congenital anomaly disorders including cat eye syndrome (CES) and DiGeorge syndrome/velocardiofacial(DGS/VCFS)(18)(19). The dosage change of significant genes could play an important role in several distinct processes such as transcription, cell differentiation, and DNA repair. When translocation occurs, although the genome may change in balance, it will also have a serious impact, such as t(15;17) occurring in acute myeloid leukemia, and t(9;22) occurring in chronic myeloid leukemia(20)(21). Recent epidemiological studies have identified an association between male infertility and cancer, and some ‘male infertility-cancer genes’ have been established as risk factors in cancer progression(22). Some shared biological processes could explain the shared etiology of cancer and male infertility, such as cell survival, cell fate, and genome maintenance(Fig.4). Disruption in any of these pathways would be expected to lead to loss or damage of germ cells and the associated expression of male infertility.
Translocations involving chromosome 17 have been thought to be harmful for the fertility of the carrier(7). The breakpoint of chromosome 17p11.2, also the critical region of SMS, was contained genes involved in several pathogenesis of cancers and reproductive physiology processes. ALKBH5 (alkB homolog 5) was an ubiquitously expressed protein in testis and brain, and was described as a cancer/testis gene(Table 2)(23). In the animal study, ALKBH5 resulted in impaired fertility by affecting meiotic metaphase-stage spermatocytes apoptosis(24). Stained testis and epididymis sections of ALKBH5 knockout male mice, observed to contain no mature sperm, but germ cells of degeneration resembling round, elongating, or elongated spermatids(25). In our patient, sperm morphology supported this result as well. Besides, DRC3 (Dynein regulatory complex subunit 3) was a critical hub for the control of flagellar motility, which was also key component of the N-DRC (nexin-dynein regulatory complex). DRC3 regulated to the waveform of flagella together with dynein g, and its mutant caused decreasing the movement speed(26). In addition, COPS3 (COP9 signalosome subunit 3), known as CSN3, is a component of the COP9 signalosome complex (CSN), which involved in various cellular and developmental processes(27). CNS3 knockout mice could not finish meiosis phase I. Meanwhile, PLD6 (phospholipase D family member 6), also known as MitoPLD, is the endonuclease that plays a critical role in PIWI-interacting RNA (piRNA) biogenesis during the spermatogenesis(28). The destruction of UBB (Ubiquitin B) gene was related to the low expression of many proteins involving in spermatogenesis and the reducing of germ cell number(29). UBB gene knockout mice were infertility, because of the structure destruction in gonad and reproductive organ, resulting in unformed gametes(30). Some other genes, such as CCDC144NL-AS1, LLGL1, FLII, TOP3A and ULK2, were involved in important functions like cell proliferation(31), embryonic development(32)(33)(34) and autophagy(35). Genes exhibit multiple physiological and pathological functions depending on the tissue and/or cell type where they are expressed(36). Thus, genes that highly expressed in testis might probably play roles in the process of sperm function and male fertility. There are still several genes, including GID4, SPECC1 and PRPSAP2, expressed highly in testis. Resulting haploinsufficiency of these genes from translocation could produce an increased risk of male infertility. Since the role of some genes remain unexplored in the development of male reproductive, studies in this direction would be very interesting in the future.
Among the individuals associated with translocation of chromosome17, the rate of unbalanced gametes was up to 81% in the case of t(17;22)(q11;q12), most of others were around 50%(37). This suggested that together with chromosome 17 and chromosome 22 might be a risk factor for abnormal meiotic segregation. Genes mapped within or just adjacent to the breakpoint region of 22q11.2 had been identified to be involved in hematological malignancies such as chronic myeloid leukemia and other disorders in development(19)(21). Among them, there was a gene, SPECC1L(sperm antigen with calponin homology and coiled-coil domains 1 like), expressed highest in testis compare to other tissues(table2). This gene was first identified to be disrupted by a balanced translocation t(1;22)(21.3;q11.23) in a female patient with bilateral oromedial-canthal (Tessier IV) clefts(38). It encoded a ‘cross-linking’ protein that functionally interacts with both microtubules and the actin cytoskeleton, which was necessary for cell adhesion and migration(39). It was also found in the cases of Opitz G/BBB syndrome, SPECC1L mutations could cause syndromic forms of facial clefting which support the original correlation to chromosome 22q11.2(40). Another gene CDC45 (cell division cycle 45) was a member of the pre-initiation complex in DNA replication, which was important for early steps of DNA replication in eukaryotes. Biallelic mutations of CDC45 caused a spectrum of phenotypes including isolated short stature and craniosynostosis(41)(42). Meanwhile, it might promote hepatocellular carcinoma (HCC) or non-small cell lung cancer (NSCLC) and correlated with worse prognosis in patients(43)(44). Another well-studied gene, T-box transcription factor 1(TBX1), had been reported that its haploinsufficiency caused abnormal growth and remodeling in the pharyngeal apparatus and related structures(45). Same as, haploid 22q11 gene insufficiency in the patients disrupt orofacial and cranial nerve development by modifying retinoic acid-modulated anterior–posterior hindbrain differentiation(46)(47). These disruptions likely contributed to dysphagia in infants and young children with 22q11DS. Several other genes in the 22q11 region had been implicated in the pathogenesis of developmental disorders. It had been reported that gene PI4KA was implicated in the pathogenesis of cerebellar hypoplasia and arthrogryposis(48). Ess2 (also termed Dgcr14) was a nuclear protein that bridged transcriptional regulators and spliceosomal complexes via distinct interacting domains, which might impact in the pathogenesis of DiGeorge syndrome(49). Gene SNAP29 has been shown to be involved in formation of primary cilia, epidermal differentiation, membrane fusion and autophagy, which implicated in a number of pathological conditions such as recessive neurocutaneous cerebral dysgenesis, neuropathy, ichthyosis, and keratoderma(50). Gene DGCR8 encodes a subunit of the microprocessor complex which mediates the biogenesis of microRNAs from the primary microRNA transcript. It could enhance Tri-negative breast cancer cell migration and invasion via targeting TGF-β(51). Taken these together, genes metioned above were associated with developmental disorder and retardation, which also the shared biological processes of cancer and infertility, might also affect in spermatogonial differentiation and spermatogenesis.
It was known that the chromosomal rearrangement associated with other chromosomal changes, particularly those involving segmental duplications, might contribute to a very genomic instability(5)(52). Many implicated risk genes in CNVs were responsible for different cellular processes, including cell signaling, sensing and repair(53). Impairment of these genes was expected to disrupt the functions specifically involved with cellular development and lead to cause diseases. In addition to the reciprocal translocation, the array analysis also revealed a novel 224.98-kb microduplication in chromosome 10q23.31. Reports of 10q duplication with other chromosomal abnormality are uncommon, and two cases with breakpoints in 10q23.31(chr10:91371499-91596485) had been reported so far. DECIPHER Patient 341717 documented with growth delay, intellectual disability and emotional lability, detected an overlapped CNVs of 8.52Mb(chr10:90100579-98618234). Similarly, DECIPHER Patient 252137 documented with phenotypes including: delayed puberty obesity, autism, cognitive impairment, intellectual disability, and abnormality of limbs, head and neck, detected an overlapped CNV of 2.63Mb(chr10:89584411-92213522).
In current study, we identified a previously unreported copy number variation at 10q23.31(chr10:91371499-91596485). This microduplication encompassed approximately four genes, FLJ37201, KIF20B, LINC00865 and PANK1(table2). None of these genes were identified in OMIM as disease causing. By now, it is unknown whether one of these genes could be dosage sensitive and responsible for the male infertility. FLJ37201 was described as tigger transposable element derived 2 pseudogene. Although pseudogenes were considered to be evolutionally conserved, they were found to act as a gene reservoir that might allowed the genome to carry out novel functions effectively(54). It was reported that pseudogenes might be present in reproductive cells more than in somatic cells(55). Moreover, transposable elements could create chromosomal insults or rearrangements and impacted gene expression, which were recognized as contributors to genomic innovations as well as genome instability(56). In this view, with a higher expression in testis, FLJ37201 could be regarded as a new candidate gene for recognizing mechanisms in male infertility. LINC00865 was a member of long noncoding RNAs (lncRNAs). lncRNAs with sequence lengths over 200 nucleotides, were considered to be regulators of many cellular processes, particularly in tumorigenesis and cancer progression(57). It had been revealed that lncRNAs could be regulated in both gene level and transcription level, and induce both cell-cycle arrest and apoptosis(58). Difference with other lncRNAs, LINC00865 was indicated highly expression in the tissue of testis, which could be recognized as a cancer/testis gene. Since its role remain unexplored in male reproductive, studies in this direction would be very interesting.
KIF20B (previously called MPHOSPH1 or MPP1) was a member of the Kinesin-6 family, which had been involved in cerebral cortex growth and midbody organization of neural stem cells in mouse(59). It could accelerate or coordinate midbody maturation, and regulate late steps of maturation in a human cell line. Meanwhile, KIF20B was found to serve important roles in multiple types of cancer, which could function as cancer-testis antigen specific to human bladder cancer (60). It also regulated cell proliferation, apoptosis and tumor growth in hepatocellular carcinoma associating with the tumor suppressor p53 (61)(62). Similarly, gene PANK1(pantothenate kinase 1) worked as a p53 transcriptional target, played an importance role in metabolic regulation, as well as modulates energy balance in the adaptive(63). Taking these into account, this 10q23.31 duplications most likely represents a risk factor for sperm immotility and abnormal sperm morphology. Increasing dosage of the four duplicate genes might disrupt diverse cellular processes, and implicated in the pathogenesis of male infertility. Since there was no evidence of a phenotypically well-defined syndrome resulting from 10q23.31 duplication so far, and its clinical significance remains unclear. Combined with the balanced reciprocal translocation t(17;22), 10q23.31 duplication could have more severe consequences for gametogenesis, and could be treated as a risk factor in our infertility patient.