Rare variants in the MECP2 gene in girls with central precocious puberty: a translational cohort study

Abstract

Background: Identification of genetic causes of central precocious puberty have revealed epigenetic mechanisms as regulators of human pubertal timing. MECP2, an X-linked gene, encodes a chromatin-associated protein with a role in gene transcription. MECP2 loss-of-function mutations usually cause Rett syndrome, a severe neurodevelopmental disorder. Early pubertal development has been shown in several patients with Rett syndrome. The aim of this study was to explore whether MECP2 variants are associated with an idiopathic central precocious puberty phenotype.

Methods: In this translational cohort study, participants were recruited from seven tertiary centres from five countries (Brazil, Spain, France, the USA, and the UK). Patients with idiopathic central precocious puberty were investigated for rare potentially damaging variants in the MECP2 gene, to assess whether MECP2 might contribute to the cause of central precocious puberty. Inclusion criteria were the development of progressive pubertal signs (Tanner stage 2) before the age of 8 years in girls and 9 years in boys and basal or GnRH-stimulated LH pubertal concentrations. Exclusion criteria were the diagnosis of peripheral precocious puberty and the presence of any recognised cause of central precocious puberty (CNS lesions, known monogenic causes, genetic syndromes, or early exposure to sex steroids). All patients included were followed up at the outpatient clinics of participating academic centres. We used high-throughput sequencing in 133 patients and Sanger sequencing of MECP2 in an additional 271 patients. Hypothalamic expression of Mecp2 and colocalisation with GnRH neurons were determined in mice to show expression of Mecp2 in key nuclei related to pubertal timing regulation.

Findings: Between Jun 15, 2020, and Jun 15, 2022, 404 patients with idiopathic central precocious puberty (383 [95%] girls and 21 [5%] boys; 261 [65%] sporadic cases and 143 [35%] familial cases from 134 unrelated families) were enrolled and assessed. We identified three rare heterozygous likely damaging coding variants in MECP2 in five girls: a de novo missense variant (Arg97Cys) in two monozygotic twin sisters with central precocious puberty and microcephaly; a de novo missense variant (Ser176Arg) in one girl with sporadic central precocious puberty, obesity, and autism; and an insertion (Ala6_Ala8dup) in two unrelated girls with sporadic central precocious puberty. Additionally, we identified one rare heterozygous 3'UTR MECP2 insertion (36_37insT) in two unrelated girls with sporadic central precocious puberty. None of them manifested Rett syndrome. Mecp2 protein colocalised with GnRH expression in hypothalamic nuclei responsible for GnRH regulation in mice.

Interpretation: We identified rare MECP2 variants in girls with central precocious puberty, with or without mild neurodevelopmental abnormalities. MECP2 might have a role in the hypothalamic control of human pubertal timing, adding to the evidence of involvement of epigenetic and genetic mechanisms in this crucial biological process.

Funding: Fundação de Amparo à Pesquisa do Estado de São Paulo, Conselho Nacional de Desenvolvimento Científico e Tecnológico, and the Wellcome Trust.

Figure 1. Pedigrees of patients with central precocious puberty associated with rare heterozygous MECP2 variants.

Squares indicate male family members, circles female family members, black symbols clinically affected family members, symbols with black internal circles asymptomatic carriers, symbols with a question mark family member whose phenotype is unknown and arrows the proband in each family. Pubertal characteristics are shown for each individual; neurodevelopmental disorders are shown, when identified. The MECP2 genotype is shown for individuals whose DNA was available for genetic studies. Wt denotes wild-type genotype.

Figure 2. Schematic representation of the MECP2 gene structure (four exons) and the MECP2 protein (six protein domains). The MECP2-E1 isoform is derived from alternate splicing of exon 2 (shown in dashed lines), and it corresponds to the NM_001110792.2 transcript.

In the current study, four heterozygous MECP2 variants (shown in red) were identified in seven girls with central precocious puberty (CPP). Among them, three CPP girls had missense mutations (two in the methyl-binding domain and one in the intervening domain), while four girls had MECP2 insertions. In previous studies, five heterozygous MECP2 variants (shown in blue) were identified in six girls with Rett syndrome diagnosed with CPP (17). Among them, two Rett girls with CPP had missense mutations in the methyl-binding domain, while four girls had truncating mutations (one in the intervening domain and three in the C-terminal domain). NTD: amino-terminal domain; MBD: methyl-binding domain; ID: intervening domain; TRD: transcriptional repression domain; CTD: carboxi-terminal domain.

Figure 3. Tissue expression of Mecp2 and Gnrh in postnatal (day 38) female mouse hypothalamus.

Mecp2 is expressed in key regions for GnRH neuronal function. A) and B) Immunohistochemistry analysis revealing Mecp2 localization in the arcuate and suprachiasmatic nuclei of the hypothalamus, as well as the paraventricular hypothalamic nucleus, parvicellular division and median eminence at postnatal day 38 in female mouse. C) and D) Immunofluorescent staining for Mecp2 (in Red) confirms localization to the same regions of the hypothalamus, and E) and F) is suggestive of co-localization within the paraventricular nucleus of GnRH (in Green) and Mecp2 (in Red); DAPI nucleolar staining for the same sections (in Blue). Scale bar A-D: 100 μm; E-G: 50 μm; H-J 25 μm. Representative images of experiments performed at least 3 independent times. Arrowheads point to GnRH neurons; ARC: arcuate nucleus; SCH: suprachiasmatic nucleus; PVH; paraventricular hypothalamic nucleus; 3V: third ventricle; ME median eminence; coronal sections.