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

ABSTRACT: 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.

SUBMITTER: Li F

PROVIDER: S-EPMC8007913 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Background: Blepharophimosis-ptosis-epicanthus inversus syndrome (BPES) is an autosomal dominant disease with a low incidence rate. Indel mutations in the forkhead box L2 (FOXL2) gene cause two types of BPES that are distinguished by the presence (type I) or absence (type II) of premature ovarian failure (POF). The purpose of this study was to identify a possible deletion in FOXL2 in Chinese families with BPES and to clarify its relationship with POF. Methods: An autosomal dominant Chinese BPES family with four generations was enrolled in this study. Peripheral venous blood was collected from all affected patients, and genomic DNA was extracted from leukocytes. The whole coding sequence and nearby 5' untranslated region (UTR) and 3'UTR of the FOXL2 gene were amplified using polymerase chain reaction (PCR) with three sets of overlapping primers, followed by sequencing analyses. The sequencing results were analysed using SeqMan software. Based on the patients' clinical manifestations and analysis of the identified indel mutation, we found that the mutation disturbed interactions between FOXL2 and the StAR gene. Furthermore, through subcellular localisation and functional studies, we observed significant mislocalisation of the mutant protein; the mutant protein was found in the cytoplasm, while the wild-type protein was found in the nucleus. Loss of function was confirmed by transcriptional activity assays, quantitative real-time PCR, and electrophoretic mobility shift assays. Results: All affected patients presented with clinical features of BPES type I, including small palpebral fissures, ptosis, telecanthus, and epicanthus inversus with POF. A novel FOXL2 heterozygous indel mutation, c.19_95del, a 77-bp deletion that disrupts FOXL2 protein structure, was identified in all affected members of the family. In addition, this indel mutation significantly increased StAR mRNA expression by disrupting the ability of the FOXL2 protein to bind to the StAR promoter and act as a repressor of this gene. Conclusions: A novel FOXL2 indel mutation was identified in Chinese families with BPES. Our results expand the spectrum of known FOXL2 mutations and provide additional insight into the structure-function relationships of the FOXL2 protein. Furthermore, this novel mutation resulted in the dysfunction of FOXL2 as a transcription factor, blocking its ability to bind to the promoter region of the StAR gene, resulting in POF in the affected patient.

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

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