Confirmation of the autosomal recessive syndrome of ectopia lentis and distinctive craniofacial appearance

Unusual catalytic strategy by non-heme Fe(ii)/2-oxoglutarate-dependent aspartyl hydroxylase AspH

Biocatalytic C-H oxidation reactions are of important synthetic utility, provide a sustainable route for selective synthesis of important organic molecules, and are an integral part of fundamental cell processes. The multidomain non-heme Fe(ii)/2-oxoglutarate (2OG) dependent oxygenase AspH catalyzes stereoselective (3R)-hydroxylation of aspartyl- and asparaginyl-residues. Unusually, compared to other 2OG hydroxylases, crystallography has shown that AspH lacks the carboxylate residue of the characteristic two-His-one-Asp/Glu Fe-binding triad. Instead, AspH has a water molecule that coordinates Fe(ii) in the coordination position usually occupied by the Asp/Glu carboxylate. Molecular dynamics (MD) and quantum mechanics/molecular mechanics (QM/MM) studies reveal that the iron coordinating water is stabilized by hydrogen bonding with a second coordination sphere (SCS) carboxylate residue Asp721, an arrangement that helps maintain the six coordinated Fe(ii) distorted octahedral coordination geometry and enable catalysis. AspH catalysis follows a dioxygen activation-hydrogen atom transfer (HAT)-rebound hydroxylation mechanism, unusually exhibiting higher activation energy for rebound hydroxylation than for HAT, indicating that the rebound step may be rate-limiting. The HAT step, along with substrate positioning modulated by the non-covalent interactions with SCS residues (Arg688, Arg686, Lys666, Asp721, and Gln664), are essential in determining stereoselectivity, which likely proceeds with retention of configuration. The tetratricopeptide repeat (TPR) domain of AspH influences substrate binding and manifests dynamic motions during catalysis, an observation of interest with respect to other 2OG oxygenases with TPR domains. The results provide unique insights into how non-heme Fe(ii) oxygenases can effectively catalyze stereoselective hydroxylation using only two enzyme-derived Fe-ligating residues, potentially guiding enzyme engineering for stereoselective biocatalysis, thus advancing the development of non-heme Fe(ii) based biomimetic C-H oxidation catalysts, and supporting the proposal that the 2OG oxygenase superfamily may be larger than once perceived.

Expanding the clinical spectrum and management of Traboulsi syndrome: report on two siblings homozygous for a novel pathogenic variant in ASPH

BACKGROUND

Traboulsi syndrome is a very rare, syndromic form of ectopia lentis that is potentially sight-threatening at a young age. It is characterized by typical facial, skeletal and ocular signs.

MATERIALS AND METHODS

Two siblings, born to consanguineous parents, with a clinical phenotype consistent with Traboulsi syndrome, underwent extensive ophthalmic imaging and exome-based genetic testing. Both were treated with unilateral clear lens extraction via a limbal approach.

RESULTS

Two siblings, one male and one female, presented with systemic and ocular features consistent with Traboulsi syndrome. Lens subluxation was present in all 4fouraffected eyes, and spontaneous subconjunctival bleb formation was detected in one eye. This eye also showed evidence of keratoconus-related corneal thinning. The clinical diagnosis of Traboulsi syndrome was confirmed molecularly. A homozygous, novel, pathogenic nonsense variant was identified in exon 25 of the ASPH gene: c.2181_2183dup, p.(Val727_Trp728insTer). Excellent visual outcomes following clear lens extraction and postoperative rigid gas-permeable contact lens fitting were obtained.

CONCLUSIONS

We expanded the genetic spectrum of Traboulsi syndrome with a novel frameshift variant in the ASPH gene. We showed that lensectomy followed by gas-permeable contact lenses is an efficient therapeutic approach to treat lens subluxation in Traboulsi syndrome. However, lifelong follow-up is crucial to avoid (late) postoperative complications.

Recurrent unintentional filtering blebs after vitrectomy: A case report

A lady who underwent lensectomy for microspherophakia and pars plana vitrectomy for retinal detachment in her left eye developed recurrent filtering blebs at the site of sclerotomies. Filtering blebs were managed by suturing the sclerotomies. Targeted gene sequencing identified a variant of ASPH gene (p.Arg688Gln) which is not known to be associated with Traboulsi syndrome. But considering the paucity of cases with genetic analysis, it would be possible that p.Arg688Gln is a pathogenic variant. This is the first case report of Traboulsi syndrome due to an ASPH variant not reported earlier that can lead to recurrent filtering blebs.

A novel mutation in the aspartate beta-hydroxylase (ASPH) gene is associated with a rare form of Traboulsi syndrome

BACKGROUND

Traboulsi syndrome is a rare autosomal recessive genetic disorder. The present study aimed to identify the pathogenic variants in the ASPH gene responsible for a rare and unique presentation of Traboulsi syndrome associated with cardiac disorder.

METHODOLOGY

DNA was isolated from the blood samples from 3 clinically diagnosed Traboulsi syndrome patients (n = 3) after obtaining a prior-informed consent. All three had classical ocular and facial dysmorphic features, and two of them also had associated cardiac problems. Mutation screening was performed for the exons of ASPH gene by Sanger sequencing in these patients and 350 controls. Sequence data analysis was performed using Seqscape and insilico protein analysis by SIFT, PyMOL, and Dynamut softwares.

RESULTS

A novel homozygous variant(c.1853 T > A) in exon 21 was identified by Sanger sequencing in two of the three cases while a known pathogenic variant in exon 25 was identified in the third proband. The novel nonsense variant in exon 21 results in a premature truncation of gene resulting in a protein of 543 amino acids. This variant is not reported in ExAC, dbSNP and 1000 genome databases. Both the patients harboring this novel variant, had a unique presentation of Traboulsi syndrome with cardiac dysfunction. In silico analysis predicted the mutation to affect the calcium-binding activity of the gene which might explain the associated cardiac dysfunction in these two patients.

CONCLUSION

The novel pathogenic mutation displayed a perfect genotype-phenotype correlation in two probands of Traboulsi syndrome with cardiac dysfunction.

Whole-exome sequencing identified a novel homozygous ASPH frameshift variant causing Traboulsi syndrome in a Chinese family

Background

Traboulsi syndrome is a rare disorder characterized by ectopia lentis and facial dysmorphism (large beaked nose), which was only reported in 18 individuals to date. It is caused by homozygous/compound heterozygous variants in the aspartate/asparagine‐β‐hydroxylase (ASPH) gene, which hydroxylates the aspartic acid and asparagine in epidermal growth factor‐like domains of various proteins.

Methods

Whole‐exome and Sanger sequencing were used to identify the disease‐causing gene of the patient in a consanguineous Chinese family. Domain analysis was applied to predict the impact of the variant on ASPH protein.

Results

Through exome and Sanger sequencing, we identified a novel homozygous ASPH variant (NM_004318.4:c.1910del/NP_004309.2: p.(Asn637MetfsTer15)) in the patient, which may lead to blockage of the ASPH function through truncating the AspH oxygenase domain of the ASPH protein and/or nonsense‐mediated decay of the ASPH transcript. This is the first report of Traboulsi syndrome in a Chinese patient who was combined with ventricular septal defect, lung bullae, and recurrent spontaneous pneumothorax.

Conclusion

Our results revealed the clinical characteristics of the first Chinese patient with Traboulsi syndrome. Additionally, our study expands the mutational spectrum of Traboulsi syndrome and provides information for clinical genetic counseling to this family.

Bilateral spontaneous filtering blebs

Purpose

To report a case of bilateral spontaneous filtering bleb, scleral thinning, microspherophakia, and mild craniofacial dysmorphism.

Observations

An 18-year-old girl was referred to our clinic for evaluation of bilateral spontaneous filtering blebs. Her corrected distance visual acuity (CDVA) was 20/400 in the right eye (RE) and 20/100 in the left eye (LE). She had superior scleral thinning, multicystic filtering bleb, and microspherophakia bilaterally. The IOP was 9 mmHg in the RE and 8 mmHg in the LE. A mild craniofacial dysmorphism including downward slanting of palpebral fissures and malar hypoplasia was present. There was no sign of corneal ectasia in tomography. Anterior segment optical coherence tomography revealed the filtering blebs as subconjunctival low reflective fluid-filled spaces. Due to severe scleral thinning un the RE we performed a tectonic scleral patch graft. 6 months after surgery the depth of the anterior chamber increased and CDVA improved.

Conclusion and importance

This case indicated that the formation of spontaneous filtering blebs may occur in a syndromic condition. In any case with this symptom, special attention should be paid to craniofacial features, sclera, crystalline lens, and IOP. Tectonic scleral patch graft could be a valuable option in selected patients.

Traboulsi syndrome due to ASPH mutation: an under-recognised cause of ectopia lentis

Traboulsi syndrome is an extremely rare ophthalmological disorder characterised by facial dysmorphism, lens dislocation, anterior segment abnormalities and spontaneous filtering blebs. It is caused by pathogenic variants in the ASPH gene. To date, only 13 individuals with Traboulsi syndrome from three families have been reported in the literature. We report the first UK family with Traboulsi syndrome associated with two novel ASPH variants. This condition, which has some phenotypic overlap with both Marfan syndrome and homocystinuria, is most likely under ascertained, and we further delineate the clinical features to aid its recognition.

Loss of ciliary zonule protein hydroxylation and lens stability as a predicted consequence of biallelic ASPH variation

PURPOSE

Stability of the crystalline lens requires formation of microfibril bundles and their higher-order structures of ciliary zonules. Trauma, malformation, or degeneration of the ciliary zonules can lead to dislocation or displacement of the lens, which in turn can cause transient or permanent loss of visual acuity. The purpose of this study was to identify the predicted substrates of aspartyl/asparaginyl hydroxylase (ASPH), a 2-oxoglutarate- and Fe²⁺-dependent hydroxylase, which may account for the lens instability phenotype of ASPH-associated syndromes.

METHODS

A single proband of European ancestry with spherophakia and high myopia was subjected to exome sequencing. Proteins containing the ASPH hydroxylation motif were identified within the SwissProt protein database.

RESULTS

We identified 105 putative substrates of ASPH-mediated hydroxylation in the human proteome, of which two (fibrillin-1 and latent transforming growth factor beta binding protein-2) are associated with inherited ectopia lentis syndromes, and are essential for microfibril and ciliary zonule development.

CONCLUSION

Our results implicate ASPH-mediated hydroxylation in the formation of FBN1/LTBP2 microfibril bundles and competent ciliary zonules.

A novel ASPH variant extends the phenotype of Shawaf-Traboulsi syndrome

Shawaf-Traboulsi syndrome (or Traboulsi syndrome; MIM 601552) is an infrequently reported entity characterized by a typical face (long face, large nose, convex nasal ridge, underdeveloped malae, crowded teeth, retrognathia), skeletal signs (long and slender fingers, sometimes pectus deformation and hypermobile joints), and ectopia lentis with conjunctival blebs, shallow anterior chamber and iridocorneal adhesions. The entity is caused by homozygous variants in ASPH. Here, we report on a boy with the clinical diagnosis of Shawaf-Traboulsi syndrome, in whom exome sequencing allowed identification of a novel variant in ASPH. We compare the findings in the present patient to those of earlier reported patients; furthermore add new signs for this entity.

Bilateral idiopathic spontaneous filtering bleb with ectopia lentis: A case report and review of literature

A 26-year-old male presented with superior filtering bleb with scleral thinning, dislocated lens, and hypotony in both the eyes. His cornea was normal without any sign of ectasia, and there was no history of recurrent redness, trauma, or surgery in either eye. Anterior segment optical coherence tomography did not reveal communicating fistula between the anterior chamber and subconjunctival space. Physical examination and blood investigations did not reveal any systemic association. He was diagnosed to have spontaneous filtering bleb, which is a rare condition observed with ocular or systemic abnormalities.

Mutations in ASPH cause facial dysmorphism, lens dislocation, anterior-segment abnormalities, and spontaneous filtering blebs, or Traboulsi syndrome

We have previously described a syndrome characterized by facial dysmorphism, lens dislocation, anterior-segment abnormalities, and spontaneous filtering blebs (FDLAB, or Traboulsi syndrome). In view of the consanguineous nature of the affected families and the likely autosomal-recessive inheritance pattern of this syndrome, we undertook autozygosity mapping and whole-exome sequencing to identify ASPH as the disease locus, in which we identified two homozygous mutations. ASPH encodes aspartyl/asparaginyl β-hydroxylase (ASPH), which has been found to hydroxylate aspartic acid and asparagine residues on epidermal growth factor (EGF)-domain-containing proteins. The truncating and missense mutations we identified are predicted to severely impair the enzymatic function of ASPH, which suggests a possible link to other forms of ectopia lentis given that many of the genes implicated in this phenotype encode proteins that harbor EGF domains. Developmental analysis of Asph revealed an expression pattern consistent with the proposed link to the human syndrome. Indeed, Asph-knockout mice had a foreshortened snout, which corresponds to the facial abnormalities in individuals with Traboulsi syndrome. These data support a genetic basis for a syndromic form of ectopia lentis and the role of aspartyl hydroxylation in human development.

Results of fibrillin-1 gene analysis in children from inbred families with lens subluxation

BACKGROUND

Autosomal dominant mutation of the FBN1 gene (fibrillin-1) results in a spectrum of disease (type 1 fibrillopathies) ranging from Marfan syndrome with lens subluxation and cardiovascular complications to milder connective tissues phenotypes. The likelihood of FBN1 mutation in children referred to ophthalmologists because of lens subluxation is unclear. We report the results of routine FBN1 sequencing for children from inbred families referred with nontraumatic lens subluxation without cataract or vitreoretinal degeneration.

METHODS

Medical records of such patients from 2009 to 2012 were retrospectively reviewed.

RESULTS

Eight identified probands (3-11 years old; 4 boys) from consanguineous and/or endogamous Saudi Arabian families all harbored FBN1 mutation--7 autosomal dominant and 1 autosomal recessive (homozygous). Four mutations were novel. One child had a family history for lens subluxation. Seven had facial and/or skeletal features suggestive of type 1 fibrillinopathy. The parents of the autosomal recessive case were confirmed to be heterozygous carriers without lens subluxation or other clinical signs of type 1 fibrillinopathy.

CONCLUSIONS

Autosomal dominant type 1 fibrillinopathy was the major cause for lens subluxation in this cohort despite the fact that families were inbred and thus at higher risk for recessive disease. This highlights the frequency of new mutations in the gene and has important implications for genetic counseling and systemic assessment. The autosomal recessive case represents the fourth such case reported to date. Her heterozygous parents were unaffected carriers, suggesting that some FBN1 mutations can act as hypomorphic alleles rather than exhibiting the dominant negative effect typically attributed to FBN1 mutations.

Anterior segment imaging and treatment of a case with syndrome of ectopia lentis, spontaneous filtering blebs, and craniofacial dysmorphism

Purpose

To report the ultrasound biomicroscopy (UBM) and surgical findings in a subject with a syndrome of ectopia lentis, spontaneous filtering blebs, and craniofacial dysmorphism (Traboulsi syndrome).

Methods

Case report, using a 40-MHz UBM wide-field anterior segment scan and anterior segment optical coherence tomography (OCT).

Results

A 16-year-old orphan girl presented with visual loss to the level of 6/60 (20/200) bilaterally. She had a central corneal opacification with retrocorneal fibrosis. The anterior chamber was flat with a very poorly dilating pupil. The lens was central in location. Perilimbal conjunctival blebs were bilateral with an intraocular pressure of 8 mm Hg. UBM and anterior segment OCT revealed chronic apposition of the iris to the cornea with angle closure, delineation of the bleb tract and rarefaction of the zonules. The girl had abnormal facial features (a beaked nose and long face) with normal chromosomal studies, negative fluorescent in situ hybridization study for velocardiofacial syndrome and an absence of signs suggesting Marfan syndrome. Under general anesthesia, attempts at deepening the anterior chamber with sodium hyaluronate 3% led to a spontaneous dislocation of the lens into the anterior chamber, facilitating its aspiration. Deepening of the angle was found after lens removal. Retrocorneal fibrosis persisted after surgery, but the bleb height decreased. Best corrected visual acuity did not improve from the preoperative level beyond 6/60 (20/200) because of central retrocorneal fibrosis.

Conclusions

Early surgical removal of the lens is necessary in this syndrome to avoid irreversible corneal and trabecular meshwork damage in chronic apposition of the iris to the cornea. UBM can help in the delineation of the bleb tract and document resolution of angle closure after surgery.

Anterior axial lens subluxation, progressive myopia, and angle-closure glaucoma: recognition and treatment of atypical presentation of ectopia lentis

PURPOSE

To describe the clinical features of an atypical presentation of ectopia lentis consisting of primary anterior axial lens subluxation in childhood, associated progressive myopia, and complicating angle-closure glaucoma; to facilitate early diagnosis of this triad; and to report the results of lensectomy for treatment.

METHODS

A retrospective case review of eight patients. Clinical course, visual acuity, gonioscopy, axial length, refraction, fundus examination, associated systemic features, and results of treatment are provided.

RESULTS

This subgroup of patients with ectopia lentis is at risk for progressive, synechial, angle-closure glaucoma. Identification of a clinical triad consisting of rapidly increasing myopia, normal axial length, and progressive axial subluxation leads to earlier diagnosis. Prophylactic lensectomy provides a safe and sight-saving treatment that arrests and, at times, reverses the progression of angle-closure glaucoma.

CONCLUSIONS

Ectopia lentis with anterior axial subluxation and progressive myopia can be a sight-threatening condition when significant forward mobilization of the lens results in synechial angle-closure glaucoma. Recognition of this clinical entity can expedite diagnosis and prevent irreversible loss of vision secondary to glaucoma. Because the primary mechanism of angle closure is angle crowding, peripheral iridotomy does little to control the rise in intraocular pressure. Prophylactic lensectomy has proven to be the most reliable treatment in our experience.