New MCM8 mutation associated with premature ovarian insufficiency and chromosomal instability in a highly consanguineous Tunisian family

Objective: To identify the gene(s) involved in the etiology of premature ovarian insufficiency in a highly consanguineous Tunisian family.

Design: Genetic analysis of a large consanguineous family with several affected siblings.

Setting: University hospital-based cytogenetics and molecular genetics laboratories.

Patient(s): A highly consanguineous Tunisian family with several affected siblings born to healthy second-degree cousins.

Intervention(s): None.

Main outcome measure(s): Targeted exome sequencing was performed by next-generation sequencing for affected family members. Mutations were validated by Sanger sequencing. Functional experiments were performed to explore the deleterious effects of the identified mutation. DNA damage was induced by increasing mitomycin C (MMC) concentrations on cultured peripheral lymphocytes.

Result(s): Analysis of the next-generation sequencing data revealed a new homozygous missense mutation in the minichromosome maintenance 8 gene (MCM8).This homozygous mutation (c. 482A>C; p.His161Pro) was predicted to be deleterious and segregated with the disease in the family. MCM8 participates in homologous recombination during meiosis and DNA double-stranded break repair by dimerizing with MCM9. Mcm8 knock out results in an early block in follicle development and small gonads. Given this, we tested the chromosomal breakage repair capacity of homozygous and heterozygous MCM8 p.His161Pro mutation on cultured peripheral lymphocytes exposed to increasing MMC concentrations. We found that chromosomal breakage after MMC exposure was significantly higher in cells from homozygously affected individuals than in those from a healthy control.

Conclusion(s): Our findings provide additional support to the view that MCM8 mutations are involved in the primary ovarian insufficiency phenotype.