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

Genotype-phenotype profile of global ASPH-associated ectopia lentis and clinical findings from a Chinese cohort

BACKGROUND

Traboulsi syndrome is an under-recognized syndromic form of ectopia lentis (EL) caused by the aspartate beta-Hydroxylase (ASPH) variant. The genotype-phenotype profile of ASPH-associated disease is poorly understood due to the rarity of the condition.

METHODS

We conducted targeted next-generation sequencing and bioinformatics analysis to identify potentially pathogenic ASPH variants in the cohort. Furthermore, we characterized the expression pattern of ASPH and major components of the zonules using single-cell RNA-sequencing (scRNA-seq) and evaluated the genotype-phenotype correlations by combining our data and those from the literature.

RESULTS

We identified a novel missense variant c.2075G > A (p.G692D) and a recurrent nonsense variant c.1126C > G (p.R376*) of ASPH in two pedigrees from a Chinese cohort of EL. Both probands were 5-year-old boys with canonical facial dysmorphisms and bilateral anteriorly-dislocated lenses. Other ocular comorbidities included microspherophakia, shallow anterior chamber, and narrow chamber angel. No cardiac involvements or filtering blebs were identified. The single-cell expression atlas of ciliary epithelium demonstrated the coexpression of ASPH with FBN1, FBN2, and LTBP2 in the non-pigmented ciliary epithelium cells. Furthermore, molecular modeling simulation of p.G692D revealed increased affinity to the cb EGF-like domain and a subsequent destabilized calcium-binding motif. The genotype-phenotype analysis demonstrated that patients with cardiac involvements all harbored biallelic truncation variants.

CONCLUSIONS

The data from this study provide new insights into the genotype-phenotype profile of ASPH-associated disease and implicate the potential role of ASPH in the pathogenesis of EL.

A New Case Report of Traboulsi Syndrome: A Literature Review and Insights Into Genotype-Phenotype Correlations

Traboulsi syndrome is a rare genetic disorder characterized by facial dysmorphism, lens subluxation, anterior segment anomalies, and spontaneous filtering blebs. The syndrome is due to mutations in the ASPH gene, which plays a crucial role in the development and maintenance of the lens. This case report describes the clinical and genetic findings in a Mexican male with Traboulsi syndrome, highlighting the identification of a novel ASPH variant. A 21-year-old male presented with trauma to the right eye while playing soccer. He had a history of lens subluxation and dysmorphic facial features. Ophthalmic examination revealed right eye lens subluxation into the anterior chamber (with signs of a previous episode of acute angle closure) and left eye posterior and inferior lens subluxation with sectorial iris atrophy. Genetic analysis identified a pathogenic ASPH variant (NM_004318.3:c.1892G>A, p.Trp631*) and a novel likely pathogenic variant (deletion of exons 20-21), confirming Traboulsi syndrome. This is the first instance of Traboulsi syndrome in the Mexican population. The absence of spontaneous filtering blebs in this patient supports previous reports of the wide phenotypic variability that could be related to the type of mutation. This novel ASPH variant expands the known genetic heterogeneity of Traboulsi syndrome.

Traboulsi syndrome without features of Marfan syndrome caused by a novel homozygous ASPH variant associated with a heterozygous FBN1 variant

BACKGROUND

Traboulsi syndrome is a rare disease clinically characterized by facial dysmorphism, abnormal spontaneous filtering blebs, ectopia lentis (EL) and multiple anterior segment abnormalities.

MATERIAL AND METHODS

An 18-year-old female was referred to the Emergency Service of Hospital São Geraldo (HSG) claiming decreased right eye (RE) visual acuity associated with ocular pain that was noticed approximately 2 months earlier. She underwent a complete ophthalmic and physical examination including hands, ankle, wrist and chest X-ray, abdominal ultrasound, echocardiogram and genetic analysis (whole-exome sequencing).

RESULTS

The ophthalmic examination revealed a high myopia with spherical equivalent of - 9.50 D and best corrected visual acuity (BCVA) of 20/60 in RE and - 9.25 D with BCVA of 20/30 in the left eye (LE). Slit-lamp examination showed normal conjunctiva in both eyes (BE) and a superior-temporal cystic lesion in RE and nasal in LE; the flat anterior chamber in BE with the transparent crystalline lens touches the central corneal endothelium in the RE. Fundoscopy suggested glaucoma as the cup/disc ratio was 0.7, although the intraocular pressure (IOP) was 10 mmHg in BE without medication. Validation of data from whole exome demonstrated a novel splicing homozygous pathogenic variant (PV) (c.1765-1G>A) of the ASPH gene as well as a heterozygous variant of unknown significance (VUS) of the FBN1 gene (c.6832C>T).

CONCLUSION

We here report a novel splice-affecting homozygous pathogenic variant in the ASPH gene that was detected in a Brazilian patient with clinical features of Traboulsi syndrome.

Combined proteomic and biochemical analyses redefine the consensus sequence requirement for epidermal growth factor-like domain hydroxylation

Epidermal growth factor-like domains (EGFDs) have important functions in cell-cell signaling. Both secreted and cell surface human EGFDs are subject to extensive modifications, including aspartate and asparagine residue C3-hydroxylations catalyzed by the 2-oxoglutarate oxygenase aspartate/asparagine-β-hydroxylase (AspH). Although genetic studies show AspH is important in human biology, studies on its physiological roles have been limited by incomplete knowledge of its substrates. Here, we redefine the consensus sequence requirements for AspH-catalyzed EGFD hydroxylation based on combined analysis of proteomic mass spectrometric data and mass spectrometry-based assays with isolated AspH and peptide substrates. We provide cellular and biochemical evidence that the preferred site of EGFD hydroxylation is embedded within a disulfide-bridged macrocycle formed of 10 amino acid residues. This definition enabled the identification of previously unassigned hydroxylation sites in three EGFDs of human fibulins as AspH substrates. A non-EGFD containing protein, lymphocyte antigen-6/plasminogen activator urokinase receptor domain containing protein 6B (LYPD6B) was shown to be a substrate for isolated AspH, but we did not observe evidence for LYPD6B hydroxylation in cells. AspH-catalyzed hydroxylation of fibulins is of particular interest given their important roles in extracellular matrix dynamics. In conclusion, these results lead to a revision of the consensus substrate requirements for AspH and expand the range of observed and potential AspH-catalyzed hydroxylation in cells, which will enable future study of the biological roles of AspH.

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.

Synthesis of 2-oxoglutarate derivatives and their evaluation as cosubstrates and inhibitors of human aspartate/asparagine-β-hydroxylase

2-Oxoglutarate (2OG) is involved in biological processes including oxidations catalyzed by 2OG oxygenases for which it is a cosubstrate. Eukaryotic 2OG oxygenases have roles in collagen biosynthesis, lipid metabolism, DNA/RNA modification, transcriptional regulation, and the hypoxic response. Aspartate/asparagine-β-hydroxylase (AspH) is a human 2OG oxygenase catalyzing post-translational hydroxylation of Asp/Asn-residues in epidermal growth factor-like domains (EGFDs) in the endoplasmic reticulum. AspH is of chemical interest, because its Fe(ii) cofactor is complexed by two rather than the typical three residues. AspH is upregulated in hypoxia and is a prognostic marker on the surface of cancer cells. We describe studies on how derivatives of its natural 2OG cosubstrate modulate AspH activity. An efficient synthesis of C3- and/or C4-substituted 2OG derivatives, proceeding via cyanosulfur ylid intermediates, is reported. Mass spectrometry-based AspH assays with >30 2OG derivatives reveal that some efficiently inhibit AspH via competing with 2OG as evidenced by crystallographic and solution analyses. Other 2OG derivatives can substitute for 2OG enabling substrate hydroxylation. The results show that subtle changes, e.g. methyl- to ethyl-substitution, can significantly alter the balance between catalysis and inhibition. 3-Methyl-2OG, a natural product present in human nutrition, was the most efficient alternative cosubstrate identified; crystallographic analyses reveal the binding mode of (R)-3-methyl-2OG and other 2OG derivatives to AspH and inform on the balance between turnover and inhibition. The results will enable the use of 2OG derivatives as mechanistic probes for other 2OG utilizing enzymes and suggest 2-oxoacids other than 2OG may be employed by some 2OG oxygenases in vivo.

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.

Small-molecule active pharmaceutical ingredients of approved cancer therapeutics inhibit human aspartate/asparagine-β-hydroxylase

Human aspartate/asparagine-β-hydroxylase (AspH) is a 2-oxoglutarate (2OG) dependent oxygenase that catalyses the hydroxylation of Asp/Asn-residues of epidermal growth factor-like domains (EGFDs). AspH is reported to be upregulated on the cell surface of invasive cancer cells in a manner distinguishing healthy from cancer cells. We report studies on the effect of small-molecule active pharmaceutical ingredients (APIs) of human cancer therapeutics on the catalytic activity of AspH using a high-throughput mass spectrometry (MS)-based inhibition assay. Human B-cell lymphoma-2 (Bcl-2)-protein inhibitors, including the (R)-enantiomer of the natural product gossypol, were observed to efficiently inhibit AspH, as does the antitumor antibiotic bleomycin A2. The results may help in the design of AspH inhibitors with the potential of increased selectivity compared to the previously identified Fe(II)-chelating or 2OG-competitive inhibitors. With regard to the clinical use of bleomycin A2 and of the Bcl-2 inhibitor venetoclax, the results suggest that possible side-effects mediated through the inhibition of AspH and other 2OG oxygenases should be considered.

Diverse molecular functions of aspartate β‑hydroxylase in cancer (Review)

Aspartate/asparagine β-hydroxylase (AspH) is a type II transmembrane protein that catalyzes the post-translational hydroxylation of definite aspartyl and asparaginyl residues in epidermal growth factor-like domains of substrates. In the last few decades, accumulating evidence has indicated that AspH expression is upregulated in numerous types of human malignant cancer and is associated with poor survival and prognosis. The AspH protein aggregates on the surface of tumor cells, which contributes to inducing tumor cell migration, infiltration and metastasis. However, small-molecule inhibitors targeting hydroxylase activity can markedly block these processes, both in vitro and in vivo. Immunization of tumor-bearing mice with a phage vaccine fused with the AspH protein can substantially delay tumor growth and progression. Additionally, AspH antigen-specific CD4⁺ and CD8⁺ T cells were identified in the spleen of tumor-bearing mice. Therefore, these agents may be used as novel strategies for cancer treatment. The present review summarizes the current progress on the underlying mechanisms of AspH expression in cancer development.

Kinetic parameters of human aspartate/asparagine-β-hydroxylase suggest that it has a possible function in oxygen sensing

Human aspartate/asparagine-β-hydroxylase (AspH) is a 2-oxoglutarate (2OG)-dependent oxygenase that catalyzes the post-translational hydroxylation of Asp and Asn residues in epidermal growth factor-like domains (EGFDs). Despite its biomedical significance, studies on AspH have long been limited by a lack of assays for its isolated form. Recent structural work has revealed that AspH accepts substrates with a noncanonical EGFD disulfide connectivity (i.e. the Cys 1-2, 3-4, 5-6 disulfide pattern). We developed stable cyclic thioether analogues of the noncanonical EGFD AspH substrates to avoid disulfide shuffling. We monitored their hydroxylation by solid-phase extraction coupled to MS. The extent of recombinant AspH-catalyzed cyclic peptide hydroxylation appears to reflect levels of EGFD hydroxylation observed in vivo, which vary considerably. We applied the assay to determine the kinetic parameters of human AspH with respect to 2OG, Fe(II), l-ascorbic acid, and substrate and found that these parameters are in the typical ranges for 2OG oxygenases. Of note, a relatively high Km for O2 suggested that O2 availability may regulate AspH activity in a biologically relevant manner. We anticipate that the assay will enable the development of selective small-molecule inhibitors for AspH and other human 2OG oxygenases.

Aspartate/asparagine-β-hydroxylase: a high-throughput mass spectrometric assay for discovery of small molecule inhibitors

The human 2-oxoglutarate dependent oxygenase aspartate/asparagine-β-hydroxylase (AspH) catalyses the hydroxylation of Asp/Asn-residues in epidermal growth factor-like domains (EGFDs). AspH is upregulated on the surface of malign cancer cells; increased AspH levels correlate with tumour invasiveness. Due to a lack of efficient assays to monitor the activity of isolated AspH, there are few reports of studies aimed at identifying small-molecule AspH inhibitors. Recently, it was reported that AspH substrates have a non-canonical EGFD disulfide pattern. Here we report that a stable synthetic thioether mimic of AspH substrates can be employed in solid phase extraction mass spectrometry based high-throughput AspH inhibition assays which are of excellent robustness, as indicated by high Z'-factors and good signal-to-noise/background ratios. The AspH inhibition assay was applied to screen approximately 1500 bioactive small-molecules, including natural products and active pharmaceutical ingredients of approved human therapeutics. Potent AspH inhibitors were identified from both compound classes. Our AspH inhibition assay should enable the development of potent and selective small-molecule AspH inhibitors and contribute towards the development of safer inhibitors for other 2OG oxygenases, e.g. screens of the hypoxia-inducible factor prolyl-hydroxylase inhibitors revealed that vadadustat inhibits AspH with moderate potency.

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.

Genetics and genomics in Peru: Clinical and research perspective

Peruvians currently preserve in their DNA the history of 2.5 million years of human evolution and 150,000 years of migration from Africa to Peru or the Americas. The development of Genetics and Genomics in the clinical and academic field is shown in this review.