Compound heterozygousZP1mutations cause empty follicle syndrome in infertile sisters

Abstract

Empty follicle syndrome (EFS) is a condition in which no oocyte is retrieved from mature follicles after proper ovarian stimulation in an in vitro fertilization procedure. Genetic evidence accumulates for the etiology of recurrent EFS without pharmacological or iatrogenic problems. In this study, we present two infertile sisters in a family with EFS after three cycles of standard ovarian stimulation with human chorionic gonadotrophin and/or gonadotropin‐releasing hormone agonist therapy. Via whole‐exome sequencing and cosegregation test, we identified compound heterozygous mutations in the gene of ZP1 in both of the infertile sisters. Coimmunoprecipitation tests and homology modeling analysis confirmed that both mutated ZP1 disrupt the formation of oocyte zona pellucida by interrupting the interaction among ZP1, ZP2, and ZP3. We thus propose that the specific mutations in ZP1 gene render a causality for the intractable EFS.

Zona Pellucida Genes and Proteins: Essential Players in Mammalian Oogenesis and Fertility

“…For example, a missense mutation in exon-2, Trp83Arg, was found in a patient with degenerated oocytes and an abnormal or no ZP, and in another patient a nonsense mutation with a premature SC in exon-8, Trp471>X, had a similar phenotype [138]. A compound heterozygous mutation, Arg61Cys and Ile390Thrfs*16, was found to be associated with abnormal oocytes and no ZP since replacement of Arg61 with Cys was predicted to be deleterious to hZP1 and a frameshift mutation introducing an SC in exon-7, Ile390fs404X, resulted in a 234 aa deletion at the C-terminus of hZP1 [136,137]. In another case, two frameshift mutations in hZP1 resulted in premature SCs in exon-1, Gly57Aspfs*9, and exon-7, Ile390Thrfs*16, and apparently disrupted interactions between hZP proteins and caused degeneration of oocytes [136].…”

Homozygous Splice Site Mutation in ZP1 Causes Familial Oocyte Maturation Defect

“…However, note that even with the control sequence intron 11 is not fully spliced and some unspliced product exists in CHO cells, likely due to the small size of this intron (265 nucleotides) and its weak 3 splice site sequence that forms a hairpin impairing splicing ( Figure 4D). 123C>A p.Tyr41* Comp Het (1) No oocyte [27] 2 c.170-174del p.Gly57Aspfs*9 Comp Het (2) No oocyte [28] 3 c.181C>T p.Arg61Cys Comp Het (3) No oocyte [ (4) No oocyte [27] 15 c.1663C>T p.Arg555* Comp Het (1) No…”

“…It contains an N-terminal signal peptide (SP), a cysteine rich P-type Trefoil domain and three ZP domains (ZP-N1, ZP-N, ZP-C), a consensus furin cleavage site (CFCS) and a transmembrane domain (TMD) ( Figure 5B). During the formation of the zona pellucida, ZP1 plays a critical role by cross-linking the long chains of filaments made of consecutive alternates of ZP2, ZP3 and ZP4 [28].…”

“…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.…”