Functional study on new FOXL2 mutations found in Chinese patients with blepharophimosis, ptosis, epicanthus inversus syndrome

Novel FOXL2 variants in two Chinese families with blepharophimosis, ptosis, and epicanthus inversus syndrome

Introduction: Blepharophimosis, ptosis, and epicanthus inversus syndrome (BPES) is a rare inherited disorder. This study was aimed to identify and functionally validate FOXL2 variants in two Chinese families with BPES. Methods: The proband and his family members were subjected to whole-exome sequencing to identify disease-associated variants. Several bioinformatic tools were used to computationally predict altered proteins. In vitro functional assays were conducted by transfecting wild-type and mutant FOXL2 cDNAs into HEK-293 cells, followed by subcellular localization assays, luciferase reporter gene assays, and quantitative real-time polymerase chain reaction. Results: The clinical features of BPES, including small palpebral fissures, ptosis, telecanthus, and epicanthus inversus, were present in all affected patients. Two novel mutations were detected, c.292T>A and c.383G>T. Whole-exome sequencing analysis and prediction software suggested that these mutations were pathogenic. Functional studies showed that these two point mutations decreased FOXL2 protein expression, resulting in subcellular mislocalization and aberrant transcriptional activity of the steroidogenic acute regulatory protein gene promoter. Conclusion: Our results add to the current understanding of known FOXL2 variants in, and our in vitro experiments provide reference data and insights into the etiology of BPES. Further studies are needed to identify the possible mechanisms underlying the action of this mutation on the development of BPES.

Identification of a novel FOXL2 mutation in a fourth-generation Chinese family with blepharophimosis-ptosis-epicanthus inversus syndrome

AIM

To characterize the genetic causes and clinical features in a four-generation Chinese family with blepharophimosis-ptosis-epicanthus inversus syndrome (BPES).

METHODS

Thirteen patients with BPES and eight healthy family members were included in this study. All participants received routine ophthalmic examinations. The target next-generation sequencing (NGS) was performed to determine the causative mutation for this family. The silico analysis was also applied to predict the pathogenesis of identified mutations.

RESULTS

All patients had severe ptosis, normal intelligence, female patients have normal fertility. Genetic assessments revealed a heterozygous insertion variation in FOXL2 gene, c.672_701insGCGGCTGCCGC CGCAGCTGCTG CAGGCGCT (p.Ala234_Gly235linsAAAAAAAAGA), carried by 13 patient but absent in all unaffected members. In silico analysis supported the pathogenic nature of this highly conserved variant. This mutation resulted in the insertion of 10 amino acids into the encoded polyala nine chain, which increased the number of original polyalanine chains from 14 to 24, resulting in an extended protein.

CONCLUSION

A novel FOXL2 mutation c.672_701ins GCGGCTGCCGCCGCAGCTGCTGC AGGCGCT (p.Ala234_Gly235linsAAAAAAAAGA) was identified in a large Chinese family with BPES. This study amplified the genotypic spectrum of FOXL2-BPES and better illustrates its genotype-phenotype correlations, which provided a basis for elucidating the pathogenesis of BPES and genetic counseling.

The Genetic and Clinical Features of FOXL2-Related Blepharophimosis, Ptosis and Epicanthus Inversus Syndrome

Blepharophimosis, ptosis, and epicanthus inversus syndrome (BPES) is a craniofacial disorder caused by heterozygous variants of the forkhead box L2 (FOXL2) gene. It shows autosomal dominant inheritance but can also occur sporadically. Depending on the mutation, two phenotypic subtypes have been described, both involving the same craniofacial features: type I, which is associated with premature ovarian failure (POF), and type II, which has no systemic features. The genotype-phenotype correlation is not fully understood, but it has been hypothesised that type I BPES involves more severe loss of function variants spanning the whole gene. Type II BPES has been linked to frameshift mutations that result in elongation of the protein rather than complete loss of function. A mutational hotspot has been identified within the poly-alanine domain, although the exact function of this region is still unknown. However, the BPES subtype cannot be determined genetically, necessitating informed genetic counselling and careful discussion of family planning advice in view of the associated POF particularly as the patient may still be a child. Following puberty, female patients should be referred for ovarian reserve and response assessment. Oculofacial features can be managed with surgical intervention and regular monitoring to prevent amblyopia.

A rare association of blepharophimosis-ptosis-epicanthus inversus case with congenital nasolacrimal duct obstruction

PURPOSE

The aim of reporting this case is to describe a rare combination of blepharophimosis-ptosis-epicanthus inversus syndrome with congenital nasolacrimal duct obstruction. A variety of lacrimal anomalies have been seen in blepharophimosis-ptosis-epicanthus inversus syndrome but the occurrence of nasolacrimal duct obstruction is rare.

METHOD

The blepharophimosis-ptosis-epicanthus inversus syndrome is an autosomal dominant rare genetic defect with clinical manifestation of dysplasia of the eyelids, palpebral fissures, flat nasal bridge, and ptosis. A 20-month-old boy was referred with the complaints of watering and discharge from his right eyes since birth. On examination, the child had all the features of blepharophimosis-ptosis-epicanthus inversus syndrome with right congenital nasolacrimal duct obstruction in line with the published reports.

RESULT

On endoscopic probing and irrigation, the probe could not be visualized into the inferior meatus. On dacryoendoscopy, the membranous part of the nasolacrimal duct was found to be completely obliterated with no light transmission into the nose indicating a malformed nasolacrimal duct. The child was managed by endoscopic dacryocystorhinostomy. We could find only one case report published so far on the combination of congenital nasolacrimal duct obstruction with blepharophimosis-ptosis-epicanthus inversus syndrome. This study adds one more case of blepharophimosis-ptosis-epicanthus inversus syndrome with congenital nasolacrimal duct obstruction and adjuvant use of dacryoendoscopy.