ESPE Abstracts

Whilst several key genetic contributors to the phenotype of central precocious puberty (CPP) have been recognized, many familial cases remain without clear a genetic aetiology. Causal genetic variants are reported in imprinted genes Makorin ring finger protein 3 (MKRN3) and Delta-like homolog 1 (DLK1), alongside Kisspeptin-1 (KISS1) and (KISSR1), implicating mis-regulation of transcriptional control of the kisspeptin and GnRH neuroendocrine systems in onset of CPP. We recently published a large cohort study identifying CPP associated variants in Methyl-CpG-binding protein 2 (MECP2), a chromatin-associated transcriptional regulator, with known roles in neuronal maturation (Canton et al, Lancet Diabetes and Endocrinology, accepted). MECP2 is encoded by a gene on Xq28, is highly expressed in hypothalamic nuclei (arcuate, suprachiasmatic, and paraventricular) and co-localises with GnRH within GnRH neurons, suggesting a role in puberty onset through regulation of the GnRH neuronal axis. Loss-of-function mutations in MECP2 are usually associated with Rett syndrome, a severe neurodevelopment disorder characterized by developmental regression and intellectual disability. Interestingly, patients with Rett syndrome loss-of-function variants in MECP2 are reported with precocious puberty. Comparison of the in vitro impact of CPP-associated MECP2 variants in otherwise healthy patients, to those identified in Rett syndrome, may inform about the disparate phenotypes, aiding in differential diagnosis. We investigated the in vitro impact of 5 CPP associated and 2 Rett syndrome associated MECP2 variants in a GT1-7 mouse neuronal GnRH producing cell line. Immunocytochemistry of MECP2 variant overexpressing GT1-7 identified differential expression of CPP associated and Rett associated MECP2 variants, with lower MECP2 expression in Rett syndrome variants as compared to CPP associated variants. Variation was also observed between CPP MECP2 variants. Western blotting confirmed differential protein expression of overexpressed MECP2 variants of interest compared to wildtype MECP2. Preliminary studies in a GnRH reporter system demonstrated differential ability of MECP2 variants to supress GnRH promoter activity, suggesting a possible regulatory role in the GNRH neuronal network. Here we present data suggesting that CPP associated variants in MECP2 alter protein expression and localisation within a GnRH neuronal cell line. Mechanisms of action of gene regulation by MECP2 is complex, comprising transcriptional regulation and chromatin compaction, thus further studies are required to determine the molecular basis of MECP2 regulation of key players in GnRH neuroendocrine regulation. Identification of key differences in expression and activity of CPP associated MECP2 variants, compared to those associated with Rett syndrome, can aid in genetic diagnosis and treatment of patients.