Novel mutation in the ZP1 gene and clinical implications

Abstract

Purpose Empty follicle syndrome (EFS) is a complex reproductive disorder characterized by the repeated failure to aspirate oocytes from mature ovarian follicles during in vitro fertilization (IVF). In addition to some cases caused by iatrogenic problems and known genetic factors, there are still many unexplained aspects of EFS. Here, we aimed to assess the clinical and genetic characteristics of two EFS patients. Methods We have characterized two primary infertility patients with EFS in a nonconsanguineous family from China. Both the patients presented similar clinical phenotypes, that is a few granulosa cells but no oocytes could be retrieved during repeated cycles with normal follicular development, E2 levels, and bioavailable hCG plasma levels. Abnormal oocytes were obtained once or twice between multiple IVF cycles. We performed Sanger sequencing of the LHCGR and ZP1~ZP4 genes in the patients, and further bioinformatics analysis was performed to identify pathogenic elements in the genes. Results A novel mutation, c.181C>T (p.Arg61Cys), and a known mutation, c.1169_1176delTTTTCCCA (p.Ile390Thrfs*16), in the ZP1 gene were both identified in patient 2, but no mutations were identified in patient 1. The novel mutation inherited from her mother was absent in the control cohort and the ExAc database. The arginine residue is conserved at this position, and its replacement by cysteine was predicted to be deleterious. In another allele, a paternal frameshift mutation was predicted to introduce premature stop codons, resulting in the deletion of 234 amino acids from the C-terminus of the ZP1 protein. Conclusions Our findings presented compound heterozygous mutations in ZP1 associated with EFS and abnormal oocytes and provided further new evidence for the genetic basis of EFS and support for the genetic diagnosis of infertile individuals.

ZP4 Is Present in Murine Zona Pellucida and Is Not Responsible for the Specific Gamete Interaction

“…Several studies have analyzed the function of different ZP proteins. Recent studies in human demonstrate that mutations in ZP1 gene are related to infertility (Huang et al, 2014 ; Sun et al, 2019 ; Yuan et al, 2019 ), these mutations could affect the shuttling of glycoproteins to the secretory pathway, which would prevent the formation of the ZP around the ova, but also the formation and development of eggs (Huang et al, 2014 ; Sun et al, 2019 ; Yuan et al, 2019 ). The house mouse has provided interesting information on the functions of the different ZP proteins thanks to the use of animals genetically modified as KO and transgenic (Liu et al, 1996 ; Rankin et al, 1996 , 1999 , 2001 ; Dean, 2004 ).…”

Homozygous Splice Site Mutation in ZP1 Causes Familial Oocyte Maturation Defect

“…Human homozygous or compound heterozygous mutations reported in ZP1 result in similar albeit not identical phenotypes (Figure 2A, Table 3). Indeed, mutations in ZP1 can lead to oocyte degeneration, oocytes lacking zona pellucida or increased fragility of oocytes rendering follicular puncture tricky, ultimately resulting in an empty follicle syndrome [23][24][25][26][27][28] Among the mutations reported in the literature, seven of them (no 2,3,4,8,10,11,13 as indicated on Table 3) affect one of the zonae pellucidae domains (ZP-N1, ZP-N or ZP-C domain). These mutations result in a lack of oocytes or only degenerate oocytes.…”

“…(A) Schematic diagram of ZP1 exons is shown. The mutations identified so far on ZP1 are indicated in blue on top, numbered 1 to 17[23][24][25][26][27][28], details are given inTable 3. The bottom part indicates the newly identified nucleotide change within a sequence alignment among mammals.…”

Molecular basis of egg coat cross-linking sheds light on ZP1-associated female infertility

“…2j), suggest that hZP1-N1 cross-link formation is essential for the assembly of the human ZP and, hence, fertility. Notably, two other ZP1 variants have been found together with I390fs404X in infertile patients with empty follicle syndrome 41,43 . Similarly to I390fs404X itself, both of these mutations are expected to impair the cross-linking ability of hZP1 by either replacing an exposed residue of hZP1-N1 β-strand C with an additional Cys 41 or truncating the protein at the level of the hZP1-N1 bc loop 43 .…”

“…Against this background, the recent identification of different ZP1 mutations in infertile patients [39][40][41][42][43] argues for a much more important role of this glycoprotein in human reproduction than previously recognized. To gain molecular insights into the biological function of ZP1 and its possible relation with that of ZP4, we undertook a biochemical and structural investigation that began with the analysis of a reported case of primary female infertility associated with a frameshift mutation in the human ZP1 gene (I390fs404X) 39 .…”