Haploinsufficiency in non-homologous end joining factor 1 induces ovarian dysfunction in humans and mice.

Abstract

Premature ovarian insufficiency (POI) is a common disease in women that leads to a reduced reproductive lifespan. The aetiology of POI is genetically heterogeneous, with certain double-strand break (DSB) repair genes being implicated in POI. Although non-homologous end joining (NHEJ) is an efficient DSB repair pathway, the functional relationship between this pathway and POI remains unknown. We conducted whole-exome sequencing in a Chinese family and identified a rare heterozygous loss-of-function variant in non-homologous end joining factor 1 (<i>NHEJ1</i>): c.532C>T (p.R178*), which co-segregated with POI and irregular menstruation. The amount of NHEJ1 protein in the proband was half of the normal level, indicating a link between <i>NHEJ1</i> haploinsufficiency and POI. Furthermore, another rare heterozygous <i>NHEJ1</i> variant c.500A>G (p.Y167C) was identified in one of 100 sporadic POI cases. Both variants were predicted to be deleterious by multiple in silico tools. In vitro assays showed that knock-down of <i>NHEJ1</i> in human KGN ovarian cells impaired DNA repair capacity. We also generated a knock-in mouse model with a heterozygous <i>Nhej1</i> variant equivalent to <i>NHEJ1</i> p.R178* in familial patients. Compared with wild-type mice, heterozygous <i>Nhej1</i>-mutated female mice required a longer time to first birth, and displayed reduced numbers of primordial and growing follicles. Moreover, these mice exhibited higher sensitivity to DSB-inducing drugs. All these phenotypes are analogous to the progressive loss of ovarian function observed in POI. Our observations in both humans and mice suggest that <i>NHEJ1</i> haploinsufficiency is associated with non-syndromic POI, providing novel insights into genetic counselling and clinical prevention of POI.