Hypopituitarism in Patients with Blepharophimosis and FOXL2 Mutations

Re-analysis of gene mutations found in pituitary stalk interruption syndrome and a new hypothesis on the etiology

Background

Pituitary stalk interruption syndrome (PSIS) is a complex clinical syndrome characterized by varied pituitary hormone deficiencies, leading to severe manifestations across multiple systems. These include lifelong infertility, short stature, mental retardation, and potentially life-threatening pituitary crises if not promptly diagnosed and treated. Despite extensive research, the precise pathogenesis of PSIS remains unclear. Currently, there are two proposed theories regarding the pathogenic mechanisms: the genetic defect theory and the perinatal injury theory.

Methods

We systematically searched English databases (PubMed, Web of Science, Embase) and Chinese databases (CNKI, WanFang Med Online, Sinomed) up to February 24, 2023, to summarize studies on gene sequencing in PSIS patients. Enrichment analyses of reported mutated genes were subsequently performed using the Metascape platform.

Results

Our study included 37 articles. KEGG enrichment analysis revealed mutated genes were enriched in the Notch signaling pathway, Wnt signaling pathway, and Hedgehog signaling pathway. GO enrichment analysis demonstrated mutated genes were enriched in biological processes such as embryonic development, brain development, axon development and guidance, and development of other organs.

Conclusion

Based on our summary and analyses, we propose a new hypothesis: disruptions in normal embryonic development, partially stemming from the genetic background and/or specific gene mutations in individuals, may increase the likelihood of abnormal fetal deliveries, where different degrees of traction during delivery may lead to different levels of pituitary stalk interruption and posterior lobe ectopia. The clinical diversity observed in PSIS patients may result from a combination of genetic background, specific mutations, and variable degrees of traction during delivery.

Current understanding of the genomic abnormities in premature ovarian failure: chance for early diagnosis and management

Premature ovarian failure (POF) is an insidious cause of female infertility and a devastating condition for women. POF also has a strong familial and heterogeneous genetic background. Management of POF is complicated by the variable etiology and presentation, which are generally characterized by abnormal hormone levels, gene instability and ovarian dysgenesis. To date, abnormal regulation associated with POF has been found in a small number of genes, including autosomal and sex chromosomal genes in folliculogenesis, granulosa cells, and oocytes. Due to the complex genomic contributions, ascertaining the exact causative mechanisms has been challenging in POF, and many pathogenic genomic characteristics have yet to be elucidated. However, emerging research has provided new insights into genomic variation in POF as well as novel etiological factors, pathogenic mechanisms and therapeutic intervention approaches. Meanwhile, scattered studies of transcriptional regulation revealed that ovarian cell function also depends on specific biomarker gene expression, which can influence protein activities, thus causing POF. In this review, we summarized the latest research and issues related to the genomic basis for POF and focused on insights gained from their biological effects and pathogenic mechanisms in POF. The present integrated studies of genomic variants, gene expression and related protein abnormalities were structured to establish the role of etiological genes associated with POF. In addition, we describe the design of some ongoing clinical trials that may suggest safe, feasible and effective approaches to improve the diagnosis and therapy of POF, such as Filgrastim, goserelin, resveratrol, natural plant antitoxin, Kuntai capsule et al. Understanding the candidate genomic characteristics in POF is beneficial for the early diagnosis of POF and provides appropriate methods for prevention and drug treatment. Additional efforts to clarify the POF genetic background are necessary and are beneficial for researchers and clinicians regarding genetic counseling and clinical practice. Taken together, recent genomic explorations have shown great potential to elucidate POF management in women and are stepping from the bench to the bedside.

A human paradigm of LHX4 and NR5A1 developmental gene interaction in the pituitary gland and ovary?

The pituitary gland, as a nodal component of the endocrine system, is responsible for the regulation of growth, reproduction, metabolism, and homeostasis. Although pituitary formation though the hierarchical action of different transcription factors is well studied in mouse models, there is little evidence of the analogous developmental processes in humans. Herein, we present a female patient with a phenotype that includes blepharoptosis-ptosis-epicanthus syndrome and premature ovarian failure. Clinical exome sequencing revealed two heterozygous variants in two genes, LHX4 (pathogenic) and NR5A1 (VUS) genes and no mutation in FOXL2 gene. We propose a model of genetic interaction between LHX4 and NR5A1 during pituitary and ovarian development that may lead to a similar phenotype mediated by reduced FOXL2 expression.

Heterozygous variants in SIX3 and POU1F1 cause pituitary hormone deficiency in mouse and man

Congenital hypopituitarism is a genetically heterogeneous condition that is part of a spectrum disorder that can include holoprosencephaly. Heterozygous mutations in SIX3 cause variable holoprosencephaly in humans and mice. We identified two children with neonatal hypopituitarism and thin pituitary stalk who were doubly heterozygous for rare, likely deleterious variants in the transcription factors SIX3 and POU1F1. We used genetically engineered mice to understand the disease pathophysiology. Pou1f1 loss-of-function heterozygotes are unaffected; Six3 heterozygotes have pituitary gland dysmorphology and incompletely ossified palate; and the Six3+/-; Pou1f1+/dw double heterozygote mice have a pronounced phenotype, including pituitary growth through the palate. The interaction of Pou1f1 and Six3 in mice supports the possibility of digenic pituitary disease in children. Disruption of Six3 expression in the oral ectoderm completely ablated anterior pituitary development, and deletion of Six3 in the neural ectoderm blocked the development of the pituitary stalk and both anterior and posterior pituitary lobes. Six3 is required in both oral and neural ectodermal tissues for the activation of signaling pathways and transcription factors necessary for pituitary cell fate. These studies clarify the mechanism of SIX3 action in pituitary development and provide support for a digenic basis for hypopituitarism.

ITGB5 mutation discovered in a Chinese family with blepharophimosis-ptosis-epicanthus inversus syndrome

Blepharophimosis-ptosis-epicanthus inversus syndrome (BPES) is a rare autosomal-dominant genetic disorder, and mutations in the forkhead box L2 (FOXL2) gene are one of the major genetic causes. As this study shows, there are many patients with BPES who do not have FOXL2 mutations, as the screening results in all family members were negative. Using whole-exome sequence analysis, we discovered another possible mutational cause of BPES in integrin subunit beta 5 (ITGB5). The ITGB5 mutation (c.608T>C, p.Ile203Thr) appears in the base sequence of all BPES⁺ patients in this family, and it appears to be a three-generation-inherited mutation. It can cause changes in base sequence and protein function, and there may be cosegregation of disease phenotypes. ITGB5 is located on the long arm of chromosome three (3q21.2) and is close to the known pathogenic gene FOXL2 (3q23). This study is the first to report ITGB5 mutations in BPES, and we speculate that it may be directly involved in the pathogenesis of BPES or indirectly through the regulation of FOXL2.

The Genetics and Biology of FOXL2

FOXL2 encodes a transcription factor that regulates a wide array of target genes including those involved in sex development, eyelid development, ovarian function and maintenance, genomic integrity as well as cellular pathways such as cell-cycle progression, proliferation, and apoptosis. The role of FOXL2 has been widely studied in humans and animals. Consistent with its role in ovarian and eyelid development, over 100 germline variants in FOXL2 are associated with blepharophimosis, ptosis, and epicanthus inversus syndrome in humans, an autosomal dominant condition characterised by ovarian dysgenesis/premature ovarian insufficiency, as well as defective eyelid development. Reflecting its role in apoptosis and proliferation, a somatic variant in FOXL2 causes adult granulosa cell tumours in humans. Despite being widely studied and having clear relevance to human disease, much remains unknown about the genes FOXL2 regulates and how it exerts its wide-reaching effect on multiple organs. This review focuses on FOXL2 and its varied roles as a transcription factor in sex determination, ovarian maintenance and function, eyelid development, genome integrity, and cell regulation, followed by discussion of the in vivo disruption of FOXL2 in humans and other species.

A Novel Forkhead Box L2 Missense Mutation, c.1068G>C, in a Chinese Family With Blepharophimosis/Ptosis/Epicanthus Inversus Syndrome

ABSTRACT

The aim of the study was to report a novel forkhead box L2 (FOXL2) missense mutation in a Chinese blepharophimosis/ptosis/epicanthus inversus syndrome family. Three generations of the Chinese family with blepharophimosis/ptosis/epicanthus inversus syndrome were enrolled in this study. Blood samples from patients of this family were collected and then analyzed by whole-exome sequencing. Confocal microscopy was performed to detect the subcellular location of FOXL2. Transactivation studies were performed and verified with real time polymerase chain reaction. A novel mutation (c.1068G>C) located in the downstream of deoxyribonucleic acid-binding forkhead domain was identified. Confocal photos showed the novel mutation did not disturb FOXL2 function, and the mutant protein could still transactivate steroidogenic acute regulatory protein, a key regulator of primary ovarian failure (POF). Our study revealed a novel missense mutation (c.1068G>C) and expanded the spectrum of FOXL2 gene mutations.

Functional Studies of Novel FOXL2 Variants in Chinese Families With Blepharophimosis-Ptosis-Epicanthus Inversus Syndrome

The blepharophimosis-ptosis-epicanthus inversus syndrome (BPES) is a rare autosomal dominant disease mainly caused by FOXL2 variants. This genetic disorder is usually characterized by eyelid malformation and ovarian dysfunction. However, no reliable genotype/phenotype correlations have been established considering the ovarian phenotype. Here, we detected 15 FOXL2 variants including nine novel ones from 7 families and 8 sporadic cases, which expanded the spectrum of FOXL2 variants and identified a potential clinical cause. Functional studies, with respect to the effect of FOXL2 on the StAR promoter, showed that non-sense variants that lead to protein truncation before the polyalanine tract and missense variants [c.307C > T; p.(Arg103Cys), c.311A > C; p.(His104Pro), c.320G > A; p.(Ser107Asn), and c.335T > A; p.(Phe112Tyr)] within the central portion of the FOXL2 forkhead domain significantly affect its suppressor activity. Such changes may explain the mechanism underlying a more severe phenotype, more likely to result in BPES type I. Furthermore, the missenses variants c.307C > T; p.(Arg103Cys), c.311A > C; p.(His104Pro), and c.320G > A; p.(Ser107Asn) were not able to transactivate OSR2, which is consistent with the eyelid malformation in these patients. The results from our cohort have expanded the spectrum of FOXL2 variants and have provided insights into genotype/phenotype correlations.