Mucopolysaccharidoses and the eye

Non-syndromic retinal dystrophy associated with biallelic variation of SUMF1 and reduced leukocyte sulfatase activity

Biallelic variants in SUMF1 are associated with multiple sulfatase deficiency (MSD), a rare lysosomal storage disorder typically diagnosed in early infancy or childhood, marked by severe neurodegeneration and early mortality. We present clinical and molecular characterisation of three unrelated patients aged 13 to 58 years with milder clinical manifestations due to SUMF1 disease variants, including two adult patients presenting with apparent non-syndromic retinal dystrophy. Whole genome sequencing identified biallelic SUMF1 variants in all three patients; Patient 1 homozygous for a complex allele c.[290G>T;293T>A]; p.[(Gly97Val);(Val98Glu)], Patient 2 homozygous for c.866A>G; p.(Tyr289Cys), and Patient 3 compound heterozygous for c.726-1G>C and p.(Tyr289Cys). Electroretinography indicated a rod-cone dystrophy with additional possible inner retinal dysfunction in all three patients. Biochemical studies confirmed reduced, but not absent, sulfatase enzyme activity in the absence of extra-ocular disease (Patient 1) or only mild systemic disease (Patients 2, 3). These cases are suggestive that non-null SUMF1 genotypes can cause an attenuated clinical phenotype, including retinal dystrophy without systemic complications, in adulthood.

Late-onset mucopolysaccharidosis type IIIA mimicking Usher syndrome

Mucopolysaccharidosis type IIIA (MPS IIIA or Sanfilippo syndrome type A) is an autosomal recessive lysosomal storage disorder caused by pathogenic variants in the SGSH gene encoding N-sulfoglucosamine sulfohydrolase, an enzyme involved in the degradation of heparan sulfate. MPS IIIA is typically characterized by neurocognitive decline and hepatosplenomegaly with childhood onset. Here, we report on a 53-year-old male subject initially diagnosed with Usher syndrome for the concurrence of retinitis pigmentosa and sensorineural hearing loss. Clinical exome sequencing identified biallelic missense variants in SGSH, and biochemical assays showed complete deficiency of sulfamidase activity and increased urinary glycosaminoglycan excretion. Reverse phenotyping revealed left ventricle pseudo-hypertrophy, hepatosplenomegaly, bilateral deep white matter hyperintensities upon brain MRI, and decreased cortical metabolic activity by PET-CT. On neuropsychological testing, the proband presented only partial and isolated verbal memory deficits. This case illustrates the power of unbiased, comprehensive genetic testing for the diagnosis of challenging mild or atypical forms of MPS IIIA.

Multisystem Involvement in a Pediatric Patient With Suspected Mucopolysaccharidosis: A Case Report

Mucopolysaccharidoses (MPS) are a group of inherited metabolic disorders characterized by the deficiency or malfunction of lysosomal enzymes responsible for glycosaminoglycan (GAG) degradation. We present the case of an 11-year-old male with a history of calcified mitral valve, rheumatic heart disease, and growth hormone deficiency who presented with dyspnea on exertion. Physical examination revealed dysmorphic facial features, short stature, and suboptimal weight and height parameters. Magnetic resonance imaging (MRI) of the brain showed cystic lesions in the white matter and corpus callosum, hydrocephalus, and cerebral atrophy, suggestive of MPS. This case highlights the importance of considering MPS in the differential diagnosis of patients with multisystemic involvement and the utility of advanced imaging techniques like MRI in guiding diagnosis and management. A multidisciplinary approach involving cardiology, endocrinology, genetics, and neurology is crucial for comprehensive management and improving patient outcomes. Early diagnosis and intervention are essential in optimizing the quality of life for patients with MPS.

Syndromic Retinitis Pigmentosa: A 15-Patient Study

Retinitis pigmentosa is a group of genetically determined retinal dystrophies characterized by primary photoreceptor apoptosis and can occur in isolated or syndromic conditions. This study reviewed the clinical data of 15 patients with syndromic retinitis pigmentosa from a Rare Disease Reference Center in Brazil and the results of their next-generation sequencing tests. Five males and ten females participated, with the mean ages for ocular disease onset, fundoscopic diagnosis, and molecular evaluation being 9, 19, and 29 years, respectively. Bardet-Biedl syndrome (n = 5) and Usher syndrome (n = 3) were the most frequent diagnoses, followed by other rare conditions. Among the patients, fourteen completed molecular studies, with three negative results and eleven revealing findings in known genes, including novel variants in MKKS (c.432_435del, p.Phe144Leufs*14), USH2A (c.(7301+1_7302-1)_(9369+1_9370-1)del), and CEP250 (c.5383dup, p.Glu1795Glyfs*13, and c.5050del, p.Asp1684Thrfs*9). Except for Kearn-Sayre, all presented an autosomal recessive inheritance pattern with 64% homozygosity results. The long gap between symptom onset and diagnosis highlights the diagnostic challenges faced by the patients. This study reaffirms the clinical heterogeneity of syndromic retinitis pigmentosa and underscores the pivotal role of molecular analysis in advancing our understanding of these diseases.

Ocular manifestations of liver disease: an important diagnostic aid

PURPOSE

This review examined existing literature to determine various ocular manifestations of liver pathologies, with a focus on metabolic deficiencies as well as viral and immune liver conditions.

METHODS

Recent data were compiled from PubMed from 2000 to 2020 using keywords that were relevant to the assessed pathologies. Ocular presentations of several liver pathologies were researched and then summarized in a comprehensive form.

RESULTS

Several ocular manifestations of liver disease were related to vitamin A deficiency, as liver disease is associated with impaired vitamin A homeostasis. Alcoholic liver cirrhosis can result in vitamin A deficiency, presenting with Bitot spots, xerosis, and corneal necrosis. Congenital liver diseases such as mucopolysaccharidoses and peroxisomal disorders are also linked with ocular signs. Viral causes of liver disease have associations with conditions like retinal vasculitis, keratoconjunctivitis sicca, retinopathies, Mooren's ulcer, and Sjogren's syndrome. Autoimmune hepatitis has been linked to peripheral ulcerative keratitis and uveitis.

CONCLUSIONS

Building strong associations between ocular and liver pathology will allow for early detection of such conditions, leading to the early implementation of management strategies. While this review outlines several of the existing connections between hepatic and ophthalmic disease, further research is needed in the area in order to strengthen these associations.

Repetitive, non-invasive imaging of neurodegeneration, and prevention of it with gene replacement, in mice with Sanfilippo syndrome

Hampering assessment of treatment outcomes in gene therapy and other clinical trials in patients with childhood dementia is the lack of an objective, non-invasive measure of neurodegeneration. Optical coherence tomography (OCT) is a widely available, rapid, non-invasive, and quantitative method for examining the integrity of the neuroretina. Profound brain and retinal dysfunction occur in patients and animal models of childhood dementia, including Sanfilippo syndrome and we recently revealed a correlation between the age of onset and rate of progression of retinal and brain degeneration in sulfamidase-deficient Sanfilippo mice. The aim of the current study was to use OCT to visualise the discrete changes in retinal structure that occur during disease progression. A progressive decline in retinal thickness was readily observable in Sanfilippo mice using OCT, with differences seen in affected animals from 10-weeks of age. OCT applied to i.v. AAV9-sulfamidase-treated Sanfilippo mice enabled visualisation of improved retinal anatomy in living animals, an outcome confirmed via histology. Importantly, brain disease lesions were also ameliorated in treated Sanfilippo mice. The findings highlight the sensitivity, ease of repetitive use and quantitative capacity of OCT for detection of discrete changes in retinal structure and their prevention with a therapeutic. Combined with the knowledge that retinal and brain degeneration are correlated in Sanfilippo syndrome, OCT provides a window to the brain in this and potentially other childhood dementias.

Mucopolysaccharidosis Type I: The Importance of Early Diagnosis for Adequate Treatment

Mucopolysaccharidoses are rare lysosomal storage disorders in which glycosaminoglycans accumulate in tissues, causing multiorgan dysfunction. Mucopolysaccharidosis type I is an autosomal recessive disease caused by a deficiency of the enzyme alpha-L-iduronidase, resulting in the accumulation of dermatan and heparan sulfate. Early diagnosis is crucial for early treatment and improved outcomes. We report the case of a female child with classic clinical features who was diagnosed early which allowed hematopoietic stem cell transplantation and slowed disease progression. She presented at birth with linea alba and umbilical and inguinal hernias. Since the first months of life, she had recurrent respiratory infections. At nine months, a motor delay was noticed, and at 20 months, craniosynostosis was corrected with surgery. Coarse facial features, thoracolumbar kyphosis, and hepatomegaly prompted a urinary glycosaminoglycan study at 22 months, which showed elevated levels. Alfa-L-iduronidase activity in dried blood spot testing was low, compatible with mucopolysaccharidosis type I. Molecular testing of gene IDUA, performed for genetic counseling, revealed the pathogenic variants c.1205G>A (p.Trp402Ter) and c.1598C>G (p.Pro533Arg) in compound heterozygosity. At 26 months, her development quotient was average for her age. She started enzyme replacement therapy at 29 months and underwent hematopoietic stem cell transplantation at 33 months, which softened the coarse features, reduced respiratory infections, and improved hepatomegaly. However, at age five, her development quotient was 76 (mean = 100, standard deviation = 15). This intellectual impairment might have been prevented with an earlier diagnosis and treatment.

Transferrin Receptor-Targeted Iduronate-2-sulfatase Penetrates the Blood-Retinal Barrier and Improves Retinopathy in Mucopolysaccharidosis II Mice

Mucopolysaccharidoses (MPSs) make up a group of lysosomal storage diseases characterized by the aberrant accumulation of glycosaminoglycans throughout the body. Patients with MPSs display various signs and symptoms, such as retinopathy, which is also observed in patients with MPS II. Unfortunately, retinal disorders in MPS II are resistant to conventional intravenous enzyme-replacement therapy because the blood-retinal barrier (BRB) impedes drug penetration. In this study, we show that a fusion protein, designated pabinafusp alfa, consisting of an antihuman transferrin receptor antibody and iduronate-2-sulfatase (IDS), crosses the BRB and reaches the retina in a murine model of MPS II. We found that retinal function, as assessed by electroretinography (ERG) in MPS II mice, deteriorated with age. Early intervention with repeated intravenous treatment of pabinafusp alfa decreased heparan sulfate deposition in the retina, optic nerve, and visual cortex, thus preserving or even improving the ERG response in MPS II mice. Histological analysis further revealed that pabinafusp alfa mitigated the loss of the photoreceptor layer observed in diseased mice. In contrast, recombinant nonfused IDS failed to reach the retina and hardly affected the retinal disease. These results support the hypothesis that transferrin receptor-targeted IDS can penetrate the BRB, thereby ameliorating retinal dysfunction in MPS II.

Mucopolysaccharidosis

Mucopolysaccharidosis are group of inherited metabolic diseases caused by the absence or malfunctioning of lysosomal enzymes resulting in accumulation of glycosaminoglycans. Over time this accumulation damages cells, tissues, and organs. There are seven types of MPS and 13 subtypes that are associated with multiple organ systems, such as the respiratory, liver, spleen, central nervous systems, arteries, skeletons, eyes, joints, ears, skin, and/or teeth. The various types share some common ocular features that differ in terms of the severity of the affection. Visual loss in MPS patients is varied and can be due to corneal clouding, glaucoma, retinopathy, and optic neuropathy. The primary focus of this review is on changes in the cornea and anterior segment in MPS patients, including clinical and novel investigative modalities, current surgical management, effects of systemic therapy like hematopoietic stem cell transplants (HSCT)and enzyme replacement therapy (ERT), as well as significant research developments.

Visual impairment in mucopolysaccharidosis VI

Mucopolysaccharidosis (MPS) VI is a rare genetic disease characterized by deficient activity of N-acetylgalactosamine 4-sulfatase, leading to the systemic deposition of glycosaminoglycans. Ocular involvement is classically characterized by progressive corneal clouding, ocular hypertension (OHT), and optic neuropathy. Although corneal clouding can be solved with penetrating keratoplasty (PK), visual impairment usually remains, being frequently attributed to glaucoma. The purpose of this study was to retrospectively describe a series of MPS VI patients with optic neuropathy in order to deepen the knowledge regarding the causes of severe visual impairment among these patients. We present five genetically confirmed clinical cases of MPS VI, treated with enzymatic replacement therapy, and with regular systemic and ophthalmologic follow-up. Corneal clouding was a common early presenting feature, leading to PK in four patients. During their follow-up, all patients developed very low visual acuities regardless of corneal grafts outcomes and controlled intraocular pressure (IOP). Furthermore, all patients exhibited optic atrophy and imagiological evidence of significant subarachnoid space enlargement and consequent optic nerve thickness reduction, suggesting compression of the optic nerve in a retro-ocular location as the cause of optic neuropathy. Although optic neuropathy in MPS VI is commonly attributed to glaucoma due to OHT, by describing a series of five MPS VI patients, we provided evidence that, differently from glaucoma, compression of optic nerve in a retro-ocular location is crucial for the development of optic neuropathy, at least in some cases. We propose the denomination of posterior glaucoma and suggest it as an important cause of optic neuropathy, leading to severe visual impairment and blindness among these patients.

Clinical and pathological characterization of ophthalmic disease in a canine model of mucopolysaccharidosis type I

Mucopolysaccharidosis type I (MPS I) is a rare lysosomal storage disease caused by α-L-iduronidase enzyme deficiency, resulting in glycosaminoglycan (GAG) accumulation in various cell types, including ocular tissues. Ocular manifestations in humans are common with significant pathological changes including corneal opacification, retinopathy, optic nerve swelling and atrophy, and glaucoma. Available treatments for MPS I are suboptimal and there is limited to no effect in treating the ocular disease. The goal of this study was to characterize the clinical and pathological features of ocular disease in a line of MPS I affected dogs, including changes not previously reported. A total of 22 dogs were studied; 12 MPS I were affected and 10 were unaffected. A subset of each underwent complete ophthalmic examination including slit lamp biomicroscopy, indirect ophthalmoscopy, rebound tonometry, and ultrasonic pachymetry. Globes were evaluated microscopically for morphological changes and GAG accumulation. Clinical corneal abnormalities in affected dogs included edema, neovascularization, fibrosis, and marked stromal thickening. Intraocular pressures were within reference interval for affected and unaffected dogs. Microscopically, vacuolated cells containing alcian blue positive inclusions were detected within the corneal stroma, iris, ciliary body, sclera, and optic nerve meninges of affected dogs. Ganglioside accumulation was identified by luxol fast blue staining in rare retinal ganglion cells. Increased lysosomal integral membrane protein-2 expression was demonstrated within the retina of affected animals when compared to unaffected controls. Results of this study further characterize ocular pathology in the canine model of MPS I and provide foundational data for future therapeutic efficacy studies.

Retinitis pigmentosa and nanophthalmos in a patient with attenuated Hunter's syndrome

PURPOSE

To describe a case of retinitis pigmentosa and nanophthalmos in a patient with attenuated Hunter's syndrome.

METHODS

Fundus photography, total field electroretinogram, ultrasound, computerized visual field examination, biochemical examination and genetic testing were obtained.

RESULTS

The fundus exam showed diffuse arteriolar attenuation, optic disc with regular contours, and pigment agglomerates like "bone spicules" in the middle periphery. Ultrasound examination revealed scleral thickening and short axial diameter in both eyes. The total field electroretinogram exam showed a subnormal result with greater impairment of the scotopic phase of the exam. Computerized visual field examination demonstrated a diffuse reduction in retinal sensitivity in the periphery. Biochemical examination showed increased urine glycosaminoglycan excretion and iduronate-2-sulphatase activity (IDS) deficiency in leukocytes, confirming the type II mucopolysaccharidosis. Molecular analysis revealed a novel missense mutation (p.A77D) in the IDS gene.

CONCLUSION

The case report is about a patient presented an attenuated form of the syndrome, with no cognitive impairment. Ophthalmologic follow-up is still an important part of multidisciplinary treatment for Hunter's syndrome.

Ocular Manifestations of Hurler-Scheie Syndrome: Recurrence of Host Disease in the Corneal Transplant

Introduction

Hurler-Scheie syndrome is a type of mucopolysaccharidosis I (MPS). In MPS I the decreased activity of alpha-L-iduronidase lysosomal enzyme leads to glycosaminoglycan (GAG) deposition in the intra- and extracellular matrix. Excessive amounts of GAG can accumulate in most layers of the cornea, including epithelial cells, stromal keratocytes, and endothelial cells.

Case Presentation

A 25-year-old female patient suffering from Hurler-Scheie syndrome with multiple ocular manifestations is reported. Due to significant bilateral corneal opacification, penetrating keratoplasty was performed on both eyes. Histopathologic examination of the corneal buttons showed disorganized collagen fibers with heterogenous thickness and many granule-containing keratocytes with excessive cytoplasm. Despite receiving enzyme replacement therapy, in vivo confocal microscopy revealed characteristic vacuoles in the basal epithelium and corneal stroma 96 months after transplantation. High resolution anterior segment optical coherence tomography demonstrated hyperreflective opacities superficial and deeper in the stroma which was consistent with recurrence of host disease in the graft.

Conclusion

To the best of our knowledge, this is the first documented Hurler-Scheie syndrome case of recurrence after penetrating keratoplasty demonstrated by in vivo confocal microscopy. Additionally, this patient manifested severe ocular involvement of MPS which might be an explanation of the progressive course of corneal opacification after transplantation.

Atypical corneal clouding in mucopolysaccharidoses

The etiology for corneal clouding from the birth is varied and includes conditions such as sclerocornea, birth trauma, corneal ulcer, Peters anomaly, and rare causes like mucopolysaccharidoses (MPS). The lysosomal storage disorders are associated with a varied ocular manifestation including bilateral corneal clouding which is often mild and stippled except in few cases like Hunter syndrome where cornea is often clear. We report a case of MPS Type I S (MPS 1) with near-normal visual acuity and bilateral dense corneal clouding with sparing of central 3 mm of cornea. The patient also had typical facial and skeletal abnormalities of lysosomal storage disorder. To our best knowledge, MPS 1 with marked corneal clouding with sparing of central cornea is very rare and has not been reported. This case report emphasizes on the atypical ocular presentation of MPS and the need for ophthalmological screening in the storage disorders.

Mucopolysaccharidosis: What Pediatric Rheumatologists and Orthopedics Need to Know

Mucopolysaccharidosis (MPS) is a group of disorders caused by the reduced or absent activity of enzymes involved in the glycosaminoglycans (GAGs) degradation; the consequence is the progressive accumulation of the substrate (dermatan, heparan, keratan or chondroitin sulfate) in the lysosomes of cells belonging to several tissues. The rarity, the broad spectrum of manifestations, the lack of strict genotype-phenotype association, and the progressive nature of MPS make diagnosing this group of conditions challenging. Musculoskeletal involvement represents a common and prominent feature of MPS. Joint and bone abnormalities might be the main clue for diagnosing MPS, especially in attenuated phenotypes; therefore, it is essential to increase the awareness of these conditions among the pediatric rheumatology and orthopedic communities since early diagnosis and treatment are crucial to reduce the disease burden of these patients. Nowadays, enzyme replacement therapy (ERT) and hematopoietic stem cell transplantation (HSCT) are available for some MPS types. We describe the musculoskeletal characteristics of MPS patients through a literature review of MPS cases misdiagnosed as having rheumatologic or orthopedic conditions.

Objectively measuring anterior segment alterations in the eyes of mucopolysaccharidoses: Its utility in early diagnosis of glaucoma

Purpose

Our study aimed to evaluate the utility of the anterior segment morphometry for objectively assessing anterior segment architectural changes of corneal clouding in the mucopolysaccharidoses (MPS) cohort and to investigate whether these measurements correlate with the slit-lamp findings on the cornea and early diagnosis of glaucoma.

Methods

This retrospective study involved 70 eyes of 35 children with cloudy cornea due to MPS variants. Anterior segment architectural alterations were measured using anterior segment imaging and biometry in MPS children and compared with controls.

Results

Mean age of the cohort at the time of assessment was 7.9 ± 4.5 years. Males constituted two-thirds of the cohort. Variants of MPS with cloudy cornea were as follows: Type I (62%), Type IV (11%), and Type VI (22%). Morphometric measurements were available in 22 eyes of 11 MPS children and an age-matched healthy control group. There were significant differences between MPS cohort and controls in refraction in Diopters (5.03 ± 0.39 and 0.01 ± 0.04; P < 0.0001), axial length (AXL) in mm (21.39 ± 0.28 and 23.04 ± 0.28; P = 0.0002), average keratometry in Diopters (40.67 ± 0.44 and 42.83 ± 0.44; P < 0.0001), anterior chamber depth (ACD) in mm (2.92 ± 0.07 and 3.65 ± 0.07; P < 0.0001), and intraocular pressure (IOP) in mmHg (25.2 ± 2.0 and 14.1 ± 2.3; P = 0.0003). Secondary glaucoma was observed in 28% of the MPS cohort.

Conclusion

The anterior segment morphometry in the cloudy cornea due to MPS provides an objective measurement of anterior segment architectural changes, thus diagnosing early-onset secondary glaucoma. These findings highlight that cloudy cornea due to MPS variants merits close monitoring throughout life.

Autophagy in the retinal pigment epithelium: a new vision and future challenges

The retinal pigment epithelium (RPE) is a highly specialized monolayer of polarized, pigmented epithelial cells that resides between the vessels of the choriocapillaris and the neural retina. The RPE is essential for the maintenance and survival of overlying light-sensitive photoreceptors, as it participates in the formation of the outer blood-retinal barrier, phagocytosis, degradation of photoreceptor outer segment (POS) tips, maintenance of the retinoid cycle, and protection against light and oxidative stress. Autophagy is an evolutionarily conserved 'self-eating' process, designed to maintain cellular homeostasis. The daily autophagy demands in the RPE require precise gene regulation for the digestion and recycling of intracellular and POS components in lysosomes in response to light and stress conditions. In this review, we discuss selective autophagy and focus on the recent advances in our understanding of the mechanism of cell clearance in the RPE for visual function. Understanding how this catabolic process is regulated by both transcriptional and post-transcriptional mechanisms in the RPE will promote the recognition of pathological pathways in genetic disease and shed light on potential therapeutic strategies to treat visual impairments in patients with retinal disorders associated with lysosomal dysfunction.

OCT imaging of macular cysts and treatment response with nepafenac in mucopolysaccharidosis type 1

PURPOSE

Mucopolysaccharidosis Type I (MPS I) is an autosomal recessive lysosomal storage disorder characterized by a defect in the enzyme alpha-L-iduronidase. Glycosaminoglycan accumulation causes ocular involvement such as corneal clouding or pigmentary retinopathy. Here we report bilateral macular cysts in mucopolysaccharidosis type I (MPS I) that responds to nepafenac treatment.

METHODS

Retrospective case report.

RESULTS

A 27-year-old woman with MPS I (Scheie phenotype) was complaining of slightly blurred vision. She had been on alpha-L-iduronidase enzyme replacement therapy for ten years. Best-corrected visual acuity was 20/25 in both eyes. Biomicroscopy was normal. Dilated fundus examination revealed pigmentary retinopathy. Optical coherence tomography (OCT) detected macular cysts in inner and outer nuclear layers, with preservation of ellipsoid zone and IS/OS line. There was no dye leakage on fluorescein angiography. Macular cysts regressed partially after one month with topical nepafenac 0.1% four times a day. BCVA improved to 20/20 in both eyes.

CONCLUSIONS

This is the first report of bilateral macular cysts that was demonstrated with OCT and treated with topical nepafenac in a patient with MPS I. Because the symptoms of our patient were mild, large-scaled cohort studies are required to ascertain the real prevalence of macular cysts in MPS I. It may also be beneficial to do more research on the possible benefits of nepafenac on the retinal manifestations of MPS.

Long-Term Outcomes of Big Bubble Deep Anterior Lamellar Keratoplasty in Mucopolysaccharidoses: A Retrospective Case Series and Review of the Literature

PURPOSE

The purpose of this study was to report the long-term surgical and visual outcomes of patients with mucopolysaccharidoses (MPS) after big bubble deep anterior lamellar keratoplasty (BB-DALK).

METHODS

This was a retrospective case series of patients with MPS who underwent BB-DALK at a single academic institution. All patients had corneal clouding secondary to MPS limiting visual acuity for which keratoplasty was indicated. Each patient was evaluated and underwent surgery by a single surgeon. Reported data included age at keratoplasty, sex, MPS type, best spectacle-corrected visual acuity, change in pachymetry, ocular comorbidities, surgical complications, and MPS-related medication use.

RESULTS

Outcomes of 12 eyes from 7 patients with MPS type I (Hurler, Scheie, and Hurler-Scheie) are reported using the newest nomenclature. The mean follow-up was 5.58 years (range: 1-10 years). All cases underwent BB-DALK with a type 1 big bubble during the surgery. Two cases (16.6%) required rebubbling because of partial Descemet membrane detachment. One case was complicated by a suture abscess and required a penetrating keratoplasty. No episodes of rejection occurred. Statistically significant improvement in the best spectacle-corrected visual acuity (from a mean 0.85-0.33 logarithm of the minimum angle of resolution, P = logarithm of the minimum angle of resolution 0.0054) and pachymetry (mean reduction of -145.4 μm, P = 0.0018) was observed.

CONCLUSIONS

BB-DALK seems to be an acceptable long-term surgical option in patients with MPS. Our findings suggest that this technique is reproducible and can achieve clear corneal grafts with good visual results on a long-term follow-up.

Novel chorioretinal findings in two siblings with mucopolysaccharidosis type VI

PURPOSE

To describe and compare the systemic and ocular findings in two siblings with mucopolysaccharidosis type VI (Maroteaux-Lamy syndrome), one treated with recombinant galsulfase, and one who was untreated.

METHOD

One female patient aged 33 years (case 1) who had received galsulfase enzyme replacement therapy for 11 years, and her younger male sibling by 3 years (case 2), who had declined systemic treatment, underwent clinical ophthalmic examination and retinal ocular coherence tomography. The female sibling underwent electrophysiology testing of visual function.

RESULTS

Case 1 had best corrected visual acuity right 6/4.8 and left 6/6. Case 2 had best corrected visual acuity of 6/6 in each eye. Case 1 had bilateral mild corneal haze and a clinically unremarkable posterior segment examination. Case 2 had bilateral very mild corneal haze and retinal striae on examination. Ocular coherence tomography showed choroidal folds at the maculae in both patients, more pronounced in Case 2, who also had retinal folds and epiretinal membrane. Electroretinography showed very mild involvement of the rods only in Case 1.

CONCLUSION

These two siblings with mucopolysaccharidosis type VI, one treated and one untreated, displayed variable levels of systemic, corneal, and chorioretinal involvement in their disease Further studies of choroidal changes in MPS VI may prove useful as a biomarker of ocular response to treatment outside the blood-retina barrier. Both patients have provided written consent to publish case details.

Mass spectrometry and two-dimensional electrophoresis in prenatal diagnosis of mucopolysaccharidosis type VI

Background

Mucopolysaccharidosis VI (MPS VI) or Maroteaux–Lamy syndrome is an autosomal recessive lysosomal storage disorder. Clinical manifestations are related to progressive accumulation of dermatan sulfate (DS). Two-dimensional electrophoresis has traditionally been used for the diagnosis of MPS disorders. The method is only qualitative and is time consuming. For prenatal diagnosis of MPS, 6–8 ml of amniotic fluid is required and 5 working days to complete. It needs personal experience to do the test and to interpret the results. Mass spectrometry (MS) is now available as a quantitative method and for prenatal diagnosis of MPS it needs less amniotic fluid and takes only 2 working days. It is more accurate, less person dependent, but it costs more. Our aim was to introduce quantitative determination of dermatan sulfate using mass spectrometry in the prenatal diagnosis of MPS VI in Egypt and to compare this technique to the classical qualitative diagnosis using two-dimensional electrophoresis (2-DEP) of the glycosaminoglycans (GAGs) in amniotic fluid. Thirty pregnant females each with single fetus were subjected to amniocentesis at 16 weeks gestation. Ten with a previously affected MPS VI infant and twenty served as controls. Prenatal diagnosis (PD) was done by both MS and 2-DEP.

Results

MS verified 2-DEP results which showed 5 affected and 5 non-affected fetuses with MPS VI.

Conclusion

Two-dimensional electrophoresis of the GAGs in amniotic fluid is a good qualitative method and MS was an accurate quantitative method for prenatal diagnosis of MPS type VI. Quantitative determination of GAGs in AF by mass spectrometry is quicker. Where prenatal diagnosis is recommended for at risk pregnancies, mass spectrometry could be used more in the future as it gives rapid and accurate results.

Molecular analysis and novel variation identification of Chinese pedigrees with mucopolysaccharidosis using targeted next-generation sequencing

BACKGROUND

Mucopolysaccharidosis (MPS) refers to a group of lysosomal storage disorders for which seven types and 11 subtypes are currently recognized. Targeted next-generation sequencing (NGS) offers an important method of disease typing, diagnosis, prenatal diagnosis, and treatment.

METHODS

Gene variations in 48 Chinese MPS patients were evaluated using NGS, and the pathogenicity of the DNA alterations was evaluated using PolyPhen2, SIFT, and Mutation Taster. The effect of amino acid substitution on protein structure was also assessed.

RESULTS

Four pedigrees with MPS I (8.3%), 28 with MPS II (58.3%), two with MPS IIIA (4.2%), two with MPS IIIB (4.2%), six with MPS IVA (12.5%), one with MPS IVB (2.1%), and five with MPS VI (10.4%) were identified. Of the 69 variations identified, 11 were novel variants (three in IDUA, five in IDS, and three in GALNS), all of which were predicted to be disease-causing except for one, and were associated with impaired protein structure and function.

CONCLUSIONS

Targeted NGS technology is effective for the gene-based testing of MPS disorders, which show high allelic heterogeneity. MPS II was the predominant form in Chinese. Our study expands the existing variation spectrum of MPS, which is important for disease management and genetic counseling.

Novel subtype of mucopolysaccharidosis caused by arylsulfatase K (ARSK) deficiency

Background

Mucopolysaccharidoses (MPS) are monogenic metabolic disorders that significantly affect the skeleton. Eleven enzyme defects in the lysosomal degradation of glycosaminoglycans (GAGs) have been assigned to the known MPS subtypes (I–IX). Arylsulfatase K (ARSK) is a recently characterised lysosomal hydrolase involved in GAG degradation that removes the 2-O-sulfate group from 2-sulfoglucuronate. Knockout of Arsk in mice was consistent with mild storage pathology, but no human phenotype has yet been described.

Methods

In this study, we report four affected individuals of two unrelated consanguineous families with homozygous variants c.250C>T, p.(Arg84Cys) and c.560T>A, p.(Leu187Ter) in ARSK, respectively. Functional consequences of the two ARSK variants were assessed by mutation-specific ARSK constructs derived by site-directed mutagenesis, which were ectopically expressed in HT1080 cells. Urinary GAG excretion was analysed by dimethylene blue and electrophoresis, as well as liquid chromatography/mass spectrometry (LC-MS)/MS analysis.

Results

The phenotypes of the affected individuals include MPS features, such as short stature, coarse facial features and dysostosis multiplex. Reverse phenotyping in two of the four individuals revealed additional cardiac and ophthalmological abnormalities. Mild elevation of dermatan sulfate was detected in the two subjects investigated by LC-MS/MS. Human HT1080 cells expressing the ARSK-Leu187Ter construct exhibited absent protein levels by western blot, and cells with the ARSK-Arg84Cys construct showed markedly reduced enzyme activity in an ARSK-specific enzymatic assay against 2-O-sulfoglucuronate-containing disaccharides as analysed by C18-reversed-phase chromatography followed by MS.

Conclusion

Our work provides a detailed clinical and molecular characterisation of a novel subtype of mucopolysaccharidosis, which we suggest to designate subtype X.

Mucopolysaccharidosis Type I-Associated Corneal Disease: A Clinicopathologic Study

PURPOSE

To report the anterior segment clinical features and histopathologic and histochemical characteristics of explanted corneas from the largest reported cohort of patients with Hurler syndrome and other variants of mucopolysaccharidosis (MPS) I undergoing corneal transplantation.

DESIGN

Retrospective observational case series.

METHODS

This institutional study reviewed 15 corneas from 9 patients with MPS I spectrum disease who underwent corneal transplant to treat corneal clouding between May 2011 and October 2020. We reviewed the clinical data, hematoxylin-eosin-stained sections, and histochemical stains, including those for mucopolysaccharides (Alcian blue and/or colloidal iron). The main outcome measures were pathology observed under light microscopy and postsurgical clinical outcomes.

RESULTS

Nine patients underwent 15 corneal transplants for corneal clouding (14/15 procedures were deep anterior lamellar keratoplasty). All corneas had mucopolysaccharide deposition visible on hematoxylin-eosin-stained sections, which was highlighted in blue with histochemical stains. All corneas also showed alterations in Bowman's layer and the majority also showed epithelial abnormalities.

CONCLUSION

MPS I shows significant corneal clouding that is successfully treated with deep anterior lamellar keratoplasty. The excised corneas show characteristic epithelial changes, disruption or breaks in Bowman's membrane, and amphophilic collections of stromal granular mucopolysaccharides which are visible on hematoxylin-eosin-stained sections and highlighted by special histochemical stains (Alcian blue and collodial iron). These changes, although subtle, should alert the pathologist to the possibility of an underlying lysosomal storage disorder.

Identification and structure characterization of novel IDS variants causing mucopolysaccharidosis type II: A retrospective analysis of 30 Chinese children

BACKGROUND

Mucopolysaccharidosis type II (MPS II) or Hunter syndrome is a rare X-linked recessive genetic disease resulting from deficient activity of the iduronate-2-sulfatase(IDS) enzyme and the accumulation of glycosaminoglycans in almost all cells, tissues and organs, which makes viscera function impaired.This study retrospectively analyzed the clinical characteristics, leukocyte IDS activity and mutations in the IDS gene of 30 Chinese children with MPS II.

METHODS

Whole-exome sequencing (WES) was performed on samples of the 30 patients.

RESULTS

A total of 25 mutations were identified in the IDS genes including 16 previously reported and 9 novel mutations (6 frameshift: c.815-818dupAACG, c.1453dupA, c.1270-1271delGT, c.1484-1485insTA, c.854delA, c.12_13delCC;3missense: c.325 T > G, c.140 T > C, c.248 T > G).The computer simulations of the protein structure analysis of the novel missense mutations showed these amino acid replacements (W109G tryptophan replaced by the glycine, L47P leucine replaced by the proline, V83G valine replaced by glycine) near the active site of IDS protein sulfatase domain and would cause a severe impairment of protein structure and function.

CONCLUSIONS

Our study expands the spectrum of MPS II genotype, provides new insights into the molecular mechanisms of MPS II, and contributes to future studies of genotype-phenotypic associations to estimate prognosis and develop new treatment regimens.

Ocular manifestations of liver disease in children: Clinical aspects and implications

Liver and eyes are interlinked to each other in various medical conditions. There are certain ocular findings which directly indicate specific liver disorders. Thus, it becomes critical to identify disorders of liver and eyes early in the course of illness, so that prompt management may be initiated before the commencement of complications. It is highly advantageous in metabolic liver disorders as it offers prognostic value and spares the patient of unnecessary invasive and detailed work up. However, due to its silent and heterogeneous presentation, it is often unrecognized and ignored. Eye abnormalities could be due to, either direct toxic effects of abnormal metabolites, excess of normal metabolites, or by deficient energy metabolism. A number of inherited liver conditions have associated ocular lesions such as Kayser-Fleischer rings in Wilson's disease, posterior embryotoxon or optic drusen in Alagille's syndrome, and cherry-red spot in Niemann-Pick's type A. A thorough eye examination is important in distinguishing between several different forms of familial intrahepatic cholestasis which are associated with anomalies of the heart, bones, or kidneys. Early diagnosis is important, as in most cases, dietary restriction and early therapy prevents the onset of disability. The aim of this review is to sensitize and make pediatricians, hepatologists and ophthalmologists aware of specific ocular findings, suggestive of certain hepatobiliary disorders, thus helping in early referral. The pediatric and adult literature was thoroughly reviewed to organize the present review.

Glaucoma Syndromes: Insights into Glaucoma Genetics and Pathogenesis from Monogenic Syndromic Disorders

Monogenic syndromic disorders frequently feature ocular manifestations, one of which is glaucoma. In many cases, glaucoma in children may go undetected, especially in those that have other severe systemic conditions that affect other parts of the eye and the body. Similarly, glaucoma may be the first presenting sign of a systemic syndrome. Awareness of syndromes associated with glaucoma is thus critical both for medical geneticists and ophthalmologists. In this review, we highlight six categories of disorders that feature glaucoma and other ocular or systemic manifestations: anterior segment dysgenesis syndromes, aniridia, metabolic disorders, collagen/vascular disorders, immunogenetic disorders, and nanophthalmos. The genetics, ocular and systemic features, and current and future treatment strategies are discussed. Findings from rare diseases also uncover important genes and pathways that may be involved in more common forms of glaucoma, and potential novel therapeutic strategies to target these pathways.

In Vivo Confocal Microscopy and Anterior Segment Optical Coherence Tomography Findings in Two Cases with Mucopolysaccharidoses

The mucopolysaccharidoses are a group of disorders caused by inherited defects in lysosomal enzymes resulting in widespread intracellular and extracellular accumulation of glycosaminoglycans. Due to the mucopolysaccharidoses subtype, glycosaminoglycans can be deposited in many organs and tissues including cornea. In this report, we presented in vivo confocal microscopy and anterior segment optical coherence tomography findings in a 39-year old man with Scheie syndrome and a 41-year old woman with Morquio syndrome (Heidelberg Retina Tomograph 3 Rostock module, Germany) and reviewed the literature. On in vivo confocal microscopy, there were multiple small and larger hyperreflective deposits in the epithelium, Bowman layer and anterior stroma and abnormally shaped, elongated keratocytes with hyporeflective round structures, which might be vacuoles in the anterior-mid stroma. In anterior segment optical coherence tomography images, accumulation of glycosaminoglycans deposits lead to an increased hypereflective appearance throughout the thickened cornea.

Enzyme Therapy: Current Challenges and Future Perspectives

In recent years, enzymes have risen as promising therapeutic tools for different pathologies, from metabolic deficiencies, such as fibrosis conditions, ocular pathologies or joint problems, to cancer or cardiovascular diseases. Treatments based on the catalytic activity of enzymes are able to convert a wide range of target molecules to restore the correct physiological metabolism. These treatments present several advantages compared to established therapeutic approaches thanks to their affinity and specificity properties. However, enzymes present some challenges, such as short in vivo half-life, lack of targeted action and, in particular, patient immune system reaction against the enzyme. For this reason, it is important to monitor serum immune response during treatment. This can be achieved by conventional techniques (ELISA) but also by new promising tools such as microarrays. These assays have gained popularity due to their high-throughput analysis capacity, their simplicity, and their potential to monitor the immune response of patients during enzyme therapies. In this growing field, research is still ongoing to solve current health problems such as COVID-19. Currently, promising therapeutic alternatives using the angiotensin-converting enzyme 2 (ACE2) are being studied to treat COVID-19.

Management of Corneal Clouding in Patients with Mucopolysaccharidosis

Mucopolysaccharidoses (MPS) are a rare group of lysosomal storage disorders characterized by the accumulation of incompletely degraded glycosaminoglycans (GAGs) in multiple organ systems including the eye. Visual loss occurs in MPS predominantly due to corneal clouding and retinopathy, but the sclera, trabecular meshwork and optic nerve may all be affected. Despite the success of therapies such as enzyme replacement therapy (ERT) and hematopoietic stem-cell transplantation (HSCT) in improving many of the systemic manifestations of MPS, their effect on corneal clouding is minimal. The only current definitive treatment for corneal clouding is corneal transplantation, usually in the form of a penetrating keratoplasty or a deep anterior lamellar keratoplasty. This article aims to provide an overview of corneal clouding, its current clinical and surgical management, and significant research progress.

Macular Corneal Dystrophy: An Updated Review

Macular Corneal Dystrophy is an autosomal recessive form of corneal dystrophy due to a mutation in CHST6 gene, which results in abnormal proteoglycan synthesis. There is accumulation of abnormal glycosaminoglycans in the corneal stroma and endothelium. The deposition results in progressive loss of corneal transparency and visual acuity. The histopathology shows characteristic alcian blue positive deposits. Management in the cases with visual loss requires keratoplasty either full thickness or lamellar. The decision about the ideal type of keratoplasty depends on age and pre-operative clinical features. Although prognosis after keratoplasty is good, recurrences can occur. Future research should be targeted towards gene therapy in this condition.

Targeting the Root Cause of Mucopolysaccharidosis IIIA with a New scAAV9 Gene Replacement Vector

No treatment is available to address the unmet needs of mucopolysaccharidosis (MPS) IIIA patients. Targeting the root cause, we developed a new self-complementary adeno-associated virus 9 (scAAV9) vector to deliver the human N-sulfoglucosamine sulfohydrolase (hSGSH) gene driven by a miniature cytomegalovirus (mCMV) promoter. In pre-clinical studies, the vector was tested at varying doses by a single intravenous (i.v.) infusion into MPS IIIA mice at different ages. The vector treatments resulted in rapid and long-term expression of functional recombinant SGSH (rSGSH) enzyme and elimination of lysosomal storage pathology throughout the CNS and periphery in all tested animals. Importantly, MPS IIIA mice treated with the vector at up to 6 months of age showed significantly improved behavior performance in a hidden task in the Morris water maze, as well as extended lifespan, with most of the animals surviving within the normal range, indicating that the vector treatment can prevent and reverse MPS IIIA disease progression. Notably, 2.5 × 1012 vector genomes (vg)/kg was functionally effective. Furthermore, the vector treatment did not lead to detectable systemic toxicity or adverse events in MPS IIIA mice. These data demonstrate the development of a safe and effective new gene therapy product for treating MPS IIIA, which further support the extended clinical relevance of platform recombinant AAV9 (rAAV9 gene delivery for treating broad neurogenetic diseases.

Mucopolysaccharidoses I and II: Brief Review of Therapeutic Options and Supportive/Palliative Therapies

Purpose. Mucopolysaccharidoses (MPS) are group of inherited lysosomal storage diseases caused by mutations of enzymes involved in catalyzing different glycosaminoglycans (GAGs). MPS I and MPS II exhibit both somatic and neurological symptoms with a relatively high disease incidence. Hematopoietic stem cell therapy (HSCT) and intravenous enzyme replacement therapy (ERT) have had a significant impact on the treatment and comprehension of disease. This review is aimed at providing a comprehensive evaluation of the pros and cons of HSCT and ERT, as well as an up-to-date knowledge of new drugs under development. In addition, multiple disease management strategies for the uncontrollable manifestations of MPS I and MPS II to improve patients' quality of life are presented. Findings. Natural history of MPS I and MPS II shows that somatic and neurological symptoms occur earlier in severe forms of MPS I than in MPS II. ERT increases life expectancy and alleviates some of the somatic symptoms, but musculoskeletal, ophthalmological, and central nervous system (CNS) manifestations are not controlled. Additionally, life-long treatment burdens and immunogenicity restriction are unintended consequences of ERT application. HSCT, another treatment method, is effective in controlling the CNS symptoms and hence has been adopted as the standard treatment for severe types of MPS I. However, it is ineffective in MPS II, which can be explained by the relatively late diagnosis. In addition, several factors such as transplant age limits or graft-versus-host disease in HSCT have limited its application for patients. Novel therapies, including BBB-penetrable-ERT, gene therapy, and substrate reduction therapy, are under development to control currently unmanageable manifestations. BBB-penetrable-ERT is being studied comprehensively in the hopes of being used in the near future as a method to effectively control CNS symptoms. Gene therapy has the potential to “cure” the disease with a one-time treatment rather than just alleviate symptoms, which makes it an attractive treatment strategy. Several clinical studies on gene therapy reveal that delivering genes directly into the brain achieves better results than intravenous administration in patients with neurological symptoms. Considering new drugs are still in clinical stage, disease management with close monitoring and supportive/palliative therapy is of great importance for the time being. Proper rehabilitation therapy, including physical and occupational therapy, surgical intervention, or medications, can benefit patients with uncontrolled musculoskeletal, respiratory, ophthalmological, and neurological manifestations.

Is the eye a window to the brain in Sanfilippo syndrome?

Sanfilippo syndrome is an untreatable form of childhood-onset dementia. Whilst several therapeutic strategies are being evaluated in human clinical trials including i.v. delivery of AAV9-based gene therapy, an urgent unmet need is the availability of non-invasive, quantitative measures of neurodegeneration. We hypothesise that as part of the central nervous system, the retina may provide a window through which to 'visualise' degenerative lesions in brain and amelioration of them following treatment. This is reliant on the age of onset and the rate of disease progression being equivalent in retina and brain. For the first time we have assessed in parallel, the nature, age of onset and rate of retinal and brain degeneration in a mouse model of Sanfilippo syndrome. Significant accumulation of heparan sulphate and expansion of the endo/lysosomal system was observed in both retina and brain pre-symptomatically (by 3 weeks of age). Robust and early activation of micro- and macroglia was also observed in both tissues. There was substantial thinning of retina and loss of rod and cone photoreceptors by ~ 12 weeks of age, a time at which cognitive symptoms are noted. Intravenous delivery of a clinically relevant AAV9-human sulphamidase vector to neonatal mice prevented disease lesion appearance in retina and most areas of brain when assessed 6 weeks later. Collectively, the findings highlight the previously unrecognised early and significant involvement of retina in the Sanfilippo disease process, lesions that are preventable by neonatal treatment with AAV9-sulphamidase. Critically, our data demonstrate for the first time that the advancement of retinal disease parallels that occurring in brain in Sanfilippo syndrome, thus retina may provide an easily accessible neural tissue via which brain disease development and its amelioration with treatment can be monitored.

Phagocytosis by the Retinal Pigment Epithelium: Recognition, Resolution, Recycling

Tissue-resident phagocytes are responsible for the routine binding, engulfment, and resolution of their meals. Such populations of cells express appropriate surface receptors that are tailored to recognize the phagocytic targets of their niche and initiate the actin polymerization that drives internalization. Tissue-resident phagocytes also harbor enzymes and transporters along the endocytic pathway that orchestrate the resolution of ingested macromolecules from the phagolysosome. Solutes fluxed from the endocytic pathway and into the cytosol can then be reutilized by the phagocyte or exported for their use by neighboring cells. Such a fundamental metabolic coupling between resident phagocytes and the tissue in which they reside is well-emphasized in the case of retinal pigment epithelial (RPE) cells; specialized phagocytes that are responsible for the turnover of photoreceptor outer segments (POS). Photoreceptors are prone to photo-oxidative damage and their long-term health depends enormously on the disposal of aged portions of the outer segment. The phagocytosis of the POS by the RPE is the sole means of this turnover and clearance. RPE are themselves mitotically quiescent and therefore must resolve the ingested material to prevent their toxic accumulation in the lysosome that otherwise leads to retinal disorders. Here we describe the sequence of events underlying the healthy turnover of photoreceptors by the RPE with an emphasis on the signaling that ensures the phagocytosis of the distal POS and on the transport of solutes from the phagosome that supersedes its resolution. While other systems may utilize different receptors and transporters, the biophysical and metabolic manifestations of such events are expected to apply to all tissue-resident phagocytes that perform regular phagocytic programs.

Multimodal imaging of Hurler syndrome-related keratopathy treated with deep anterior lamellar keratoplasty

Background

Hurler syndrome-associated keratopathy is an exceedingly rare corneal disorder that requires corneal transplantation in advanced stages. Precise assessment of the corneal condition is necessary for deciding which type of keratoplasty (i.e., deep anterior lamellar or penetrating) should be proposed. We aimed to confront the results of multimodal imaging with those of histology in a case of Hurler syndrome-associated keratopathy.

Case presentation

A 16-year-old patient with Hurler’s syndrome treated with hematopoietic stem cell transplantation was referred for decreased vision related to advanced keratopathy. The patient was treated with deep anterior lamellar keratoplasty (DALK) in both eyes with uncomplicated outcome. Visual acuity improved from 0.1 (20/200) preoperatively to 0.32 (20/63) and 0.63 (20/32) after transplantation. The corneal endothelial cell density was 2400 cells/mm² in both eyes 3 years after transplantation. In vivo confocal microscopy (IVCM) and spectral domain optical coherence tomography (SD-OCT) were performed preoperatively. The corneal buttons retrieved during keratoplasty were processed for histology. In SD-OCT scans, corneal opacities appeared as diffuse stromal hyperreflectivity associated with increased corneal thickness. IVCM showed diffuse cytoplasmic granular hyperreflectivity and rounded/ellipsoid aspects of keratocytes, presence of small intracellular vacuoles, and hyperreflective epithelial intercellular spaces. Bowman’s layer was thin and irregular. The corneal endothelium was poorly visualized but no endothelial damage was observed. Histology showed irregular orientation and organization of stromal lamellae, with the presence of macrophages whose cytoplasm appeared clear and granular. A perinuclear clear halo was visible within the epithelial basal cells. Bowman’s layer featured breaks and irregularities.

Conclusions

The observed corneal multimodal imaging features in mucopolysaccharidosis-related keratopathy were concordant with histology. Compared with standard histology, multimodal imaging allowed additional keratocyte features to be observed. It revealed both morphological and structural changes of all corneal layers but the endothelium. This information is essential for therapeutic management which should include DALK as the first-choice treatment in case of impaired visual acuity.

Mucopolysaccharidosis Type I: A Review of the Natural History and Molecular Pathology

Mucopolysaccharidosis type I (MPS I) is a rare autosomal recessive inherited disease, caused by deficiency of the enzyme α-L-iduronidase, resulting in accumulation of the glycosaminoglycans (GAGs) dermatan and heparan sulfate in organs and tissues. If untreated, patients with the severe phenotype die within the first decade of life. Early diagnosis is crucial to prevent the development of fatal disease manifestations, prominently cardiac and respiratory disease, as well as cognitive impairment. However, the initial symptoms are nonspecific and impede early diagnosis. This review discusses common phenotypic manifestations in the order in which they develop. Similarities and differences in the three animal models for MPS I are highlighted. Earliest symptoms, which present during the first 6 months of life, include hernias, coarse facial features, recurrent rhinitis and/or upper airway obstructions in the absence of infection, and thoracolumbar kyphosis. During the next 6 months, loss of hearing, corneal clouding, and further musculoskeletal dysplasias develop. Finally, late manifestations including lower airway obstructions and cognitive decline emerge. Cardiac symptoms are common in MPS I and can develop in infancy. The underlying pathogenesis is in the intra- and extracellular accumulation of partially degraded GAGs and infiltration of cells with enlarged lysosomes causing tissue expansion and bone deformities. These interfere with the proper arrangement of collagen fibrils, disrupt nerve fibers, and cause devastating secondary pathophysiological cascades including inflammation, oxidative stress, and other disruptions to intracellular and extracellular homeostasis. A greater understanding of the natural history of MPS I will allow early diagnosis and timely management of the disease facilitating better treatment outcomes.

A case study of three patients with mucopolysaccharidoses in Hue Central Hospital

Mucopolysaccharidosis is a group of rare metabolic disorders characterized by a deficiency of enzymes in the degradation of glycosaminoglycans. The incomplete degradation process leads to the accumulation of glycosaminoglycans in lysosomes of various tissues, which interferes with cell function. We report three cases that were classified as Hurler-Mucopolysaccharidosis I, Morquio-Mucopolysaccharidosis IV A, and Maroteaux-Lamy-Mucopolysaccharidosis VI. Clinical presentations of these cases vary, depending on each type of enzyme defect. All the patients appeared healthy at birth, and symptoms appear at around 1 or 2 years. Clinical features, radiological findings, and especially enzyme assays have allowed us to establish a definitive diagnosis in these cases. These cases highlight that abnormal clinical symptoms, such as growth failure, coarse facial features, and joint problems, are key points for further investigation relating to mucopolysaccharidosis disease. However, in low- and middle-income countries, it is difficult to have a definitive diagnosis of one of the mucopolysaccharidoses due to lacking enzyme assays.

Whole genome sequencing for mutation discovery in a single case of lysosomal storage disease (MPS type 1) in the dog

Mucopolysaccharidosis (MPS) is a metabolic storage disorder caused by the deficiency of any lysosomal enzyme required for the breakdown of glycosaminoglycans. A 15-month-old Boston Terrier presented with clinical signs consistent with lysosomal storage disease including corneal opacities, multifocal central nervous system disease and progressively worsening clinical course. Diagnosis was confirmed at necropsy based on histopathologic evaluation of multiple organs demonstrating accumulation of mucopolysaccharides. Whole genome sequencing was used to uncover a frame-shift insertion affecting the alpha-L-iduronidase (IDUA) gene (c.19_20insCGGCCCCC), a mutation confirmed in another Boston Terrier presented 2 years later with a similar clinical picture. Both dogs were homozygous for the IDUA mutation and shared coat colors not recognized as normal for the breed by the American Kennel Club. In contrast, the mutation was not detected in 120 unrelated Boston Terriers as well as 202 dogs from other breeds. Recent inbreeding to select for recessive and unusual coat colors may have concentrated this relatively rare allele in the breed. The identification of the variant enables ante-mortem diagnosis of similar cases and selective breeding to avoid the spread of this disease in the breed. Boston Terriers carrying this variant represent a promising model for MPS I with neurological abnormalities in humans.

Intrastromal Gene Therapy Prevents and Reverses Advanced Corneal Clouding in a Canine Model of Mucopolysaccharidosis I

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive lysosomal storage disease characterized by severe phenotypes, including corneal clouding. MPS I is caused by mutations in alpha-l-iduronidase (IDUA), a ubiquitous enzyme that catalyzes the hydrolysis of glycosaminoglycans. Currently, no treatment exists to address MPS I corneal clouding other than corneal transplantation, which is complicated by a high risk for rejection. Investigation of an adeno-associated virus (AAV) IDUA gene addition strategy targeting the corneal stroma addresses this deficiency. In MPS I canines with early or advanced corneal disease, a single intrastromal AAV8G9-IDUA injection was well tolerated at all administered doses. The eyes with advanced disease demonstrated resolution of corneal clouding as early as 1 week post-injection, followed by sustained corneal transparency until the experimental endpoint of 25 weeks. AAV8G9-IDUA injection in the MPS I canine eye with early corneal disease prevented the development of advanced corneal changes while restoring clarity. Biodistribution studies demonstrated vector genomes in ocular compartments other than the cornea and in some systemic organs; however, a capsid antibody response was detected in only the highest dosed subject. Collectively, the results suggest that intrastromal AAV8G9-IDUA therapy prevents and reverses visual impairment associated with MPS I corneal clouding.

Anterior Chamber Angles in Different Types of Mucopolysaccharidoses

PURPOSE

To evaluate the anterior chamber angle status and estimate the intraocular pressure (IOP) in patients with mucopolysaccharidoses (MPSs) type I, II, IV, and VI.

DESIGN

Prospective cross-sectional study.

METHODS

This study enrolled 27 consecutive MPS patients (8 patients with MPS I, 4 patients with MPS II, 9 patients with MPS IV, and 6 patients with MPS VI) and 20 normal control subjects. Anterior chamber angle status was evaluated by swept-source optical coherence tomography and IOP was estimated by the new-generation tonometer Corvis ST.

RESULTS

Twelve eyes (6 patients) of 15 eyes (8 patients) with MPS I had narrow angles or peripheral iridocorneal touches together with elevated IOP (80%). Six eyes (3 patients) of 8 eyes (4 patients) with MPS II had plateau iris configuration, but all 8 eyes had normal IOP. All 18 eyes (9 patients) with MPS IV had normal angle structures, but 8 eyes (4 patients) had elevated IOP (44.4%). Nine eyes (5 patients) of 11 eyes (6 patients) with MPS VI had shallow but not closed angles (81.8%). Among these 9 eyes, 5 eyes had elevated IOP, and 4 of these 5 eyes had IOP >30 mm Hg. The trabecular iris angles of MPS types I, II, and VI were smaller than those of MPS type IV and of the control subjects. The angle recess areas of MPS types I and VI were smaller than those of MPS type IV and of the control subjects.

CONCLUSIONS

MPS type I patients are prone to have glaucoma with narrow or closed angles; MPS type II patients tend to have plateau iris; MPS type IV patients are vulnerable to open-angle glaucoma; MPS type VI patients have narrow angles not as close as those of MPS type I. MPS types I, IV, and VI had higher IOP estimates than the control subjects, but only MPS I and IV had higher corrected IOP estimates than the control subjects. The ordinary IOP estimates in MPS VI patients may be falsely high because of clouded corneas and increased corneal rigidity. Swept-source optical coherence tomography helps ophthalmologist investigate the angle structure and the pathophysiology of glaucoma caused by MPS.

Enzyme replacement therapy interruption in patients with Mucopolysaccharidoses: Recommendations for distinct scenarios in Latin America

Background

Mucopolysaccharidoses (MPS) are a group of lysosomal storage disorders, leading to the progressive accumulation of glycosaminoglycans (GAGs) and the subsequent compromising of tissues and organ malfunction. Although incurable, most types of MPS can be treated with enzyme replacement therapy (ERT), an approach that has had positive effects on the natural clinical evolution and which impact has been extensively investigated. Unfortunately, to date, there is relatively little data regarding the effects of ERT interruption, especially in Latin America, where such interruption may be frequent due to a variety of issues (for instance, difficulties involving logistics, reimbursement and/or payment withdrawal).

Method

A group of medical professionals from Latin America with experience in Genetics, Pediatrics and Neurology held an Advisory Board Meeting in the city of São Paulo, in October 2018, to discuss the issue of ERT interruptions in the region and recommendations health care professionals on how to deal with these interruptions and better assess the therapeutic effects of ERT.

Conclusion

Recommendations provided by the experts may support physicians in dealing with the most common reasons for ERT interruptions in Latin America. Most importantly, recommendations for data collection at specific timepoints (at baseline, throughout the treatment and during the interruption period of ERT and after its resumption) can significantly improve the collection of real world evidence on the effects of ERT and its interruptions, supporting health care professionals and policy makers in the decision making regarding the provision of these therapies for MPS patients.

•

Positive impact of ERT is reported in MPS patients, but the effects of its interruption is overlooked.

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In Latin America, ERT interruption is not infrequent. A systematic evaluation the worsening of MPS progression is vital.

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The proposed structured data collection would help to evaluate patients and generate real word data.

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We encourage studies and experts discussions for a better understand the value of ERT for MPS patients in Latin America.

Progressive eye pathology in mucopolysaccharidosis type I mice and effects of enzyme replacement therapy

BACKGROUND

Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disorder caused by α-L-iduronidase deficiency, resulting in accumulation of glycosaminoglycans (GAG). Ophthalmological manifestations are common in MPS I patients and often lead to visual impairment. Accumulation of GAG in corneal or retinal tissues reduces vision causing corneal opacity and neurosensory complications. One available treatment for MPS I patients is enzyme replacement therapy (ERT), but the results of such treatment on eye disease are still debatable. Therefore, we aimed to determine the progression of ocular manifestations as well as the effectiveness of intravenous ERT in MPS I.

METHODS

Corneal and retinal analyses were perform in eyes from 2- to 8-month normal and MPS I mice. Some MPS I mice received ERT (1.2 mg/kg of laronidase) every 2 weeks from 6 to 8 months and histological findings were compared with controls. Additionally, cornea from two MPS I patients under ERT were evaluated.

RESULTS

Mouse corneal tissues had GAG accumulation early in life. In the retina, we found a progressive loss of photoreceptor cells, starting at 6 months. ERT did not improve or stabilize the histological abnormalities. MPS I patients, despite being on ERT for over a decade, presented GAG accumulation in the cornea, corneal thickening, visual loss and needed corneal transplantation.

CONCLUSION

We provide data on the time course of ocular alteration in MPS I mice. Our results also suggest that ERT is not effective in treating the progressive ocular manifestations in MPS I mice and fails to prevent corneal abnormalities in patients.