ESPE Abstracts

Gonadotropin-releasing hormone (GnRH) is the master hormone regulating the reproductive axis and its pulsatile secretion is crucial for puberty onset and fertility. Disruption in GnRH neuron development or hypothalamic function can lead to absent or delayed puberty (DP) due to GnRH deficiency, with a phenotypic spectrum from severe delayed puberty to partial or complete Hypogonadotropic Hypogonadism (HH). HH can also be present as a shared trait with other neurodevelopmental disorders (NDDs). The aim of our study was to identify novel genetic aetiology of severe DP by identifying variants in associated genes in our patient cohort; and ascertain the functional effects of identified variants of interest. Whole exome sequencing (WES) was performed on DNA samples from 180 probands with DP to identify potentially pathogenic rare coding variants in relevant gene pathways. Integrative analysis was performed on genomic data from human patients combined with transcriptomics analysis of rodent immortalized and primary GnRH neurons to determine novel regulators of GnRH neuronal development and function. Bone morphogenetic protein/retinoic acid inducible neural-specific 2 (BRINP2) was identified as a candidate gene of interest as it was found to be significantly upregulated during GnRH neuronal development in these single cell transcriptomics analyses. Mutations in this gene have been previously associated with NDDs such as autistic spectrum disorder (ASD). Copy number variation in this gene is seen in multiple individuals from the Deciphering Developmental Disorders study with a phenotype including cryptorchidism and intellectual disability (https://www.deciphergenomics.org/gene/BRINP2/patient-overlap/cnvs). BRINP2 is localised to the olfactory bulb, a key site during GnRH neuron migration. WES analysis identified four variants in BRINP2 (p.R726W, p.R649Q, p.I629V and p.D729N) in four unrelated probands with severely DP or partial HH, in combination with ASD or other NDD features. These four variants are all rare or ultra-rare and are predicted to be pathogenic by in silico tools including CADD, REVEL and SIFT. Protein expression of the four mutants was comparable to the reference protein. BRINP2 has been shown to inhibit neuronal cell proliferation by negative regulation of cell cycle transition and Brinp2 knockout mice show hyperactive behaviour representative of human attention-deficit hyperactivity disorder, but pubertal timing has not been assessed. Thus, BRINP2 is a novel candidate for GnRH deficiency with NDD and we have investigated the role of BRINP2 in GnRH biology via wildtype and mutant protein sub-cellular localization, as well as tissue expression in mouse hypothalamic tissue across development.