Ocular changes in long-term evolution of infantile cystinosis

[Cystinosis: From the gene identification to the first gene therapy clinical trial]

Cystinosis is an autosomal recessive metabolic disease characterized by lysosomal accumulation of cystine in all the cells of the body. Infantile cystinosis begins in infancy by a renal Fanconi syndrome and eventually leads to multi-organ failure, including the kidney, eye, thyroid, muscle, and pancreas, eventually causing premature death in early adulthood. The current treatment is the drug cysteamine that only delays the progression of the disease. We identified the gene involved, CTNS, and showed that the encoded protein, cystinosin, is a proton-driven cystine transporter. We generated a mouse model of cystinosis, the Ctns-/- mice, that recapitulates the main disease complications. The goal was next to develop a gene therapy approach for cystinosis. We used bone marrow stem cells as a vehicle to bring the healthy CTNS gene to tissues, and we showed that wild-type hematopoietic stem and progenitor cell (HSPC) transplantation led to abundant tissue integration of bone marrow-derived cells, significant decrease of tissue cystine accumulation and long-term kidney, eye and thyroid preservation. We then developed an autologous transplantation approach of HSPCs modified ex vivo using a lentiviral vector to introduce a functional CTNS cDNA, and showed its efficacy in Ctns-/- mice. We conducted the pharmacology/toxicology studies, developed the manufacturing process using human CD34+ cells, and design the clinical trial. We received Food and Drug Administration (FDA)-clearance to start a phase 1/2 clinical trial for cystinosis in December 2018. Six patients have been treated so far. In this review, we describe the path to go from the gene to a gene therapy approach for cystinosis.

Posterior Segment Involvement in Infantile Nephropathic Cystinosis - A Review

Cystinosis is a rare lysosomal storage disease with a prevalence of 1 : 100 000 - 1 : 200 000 cases. It is caused by biallelic mutations in the CTNS gene, which encodes cystinosin, that transport cystine out of the lysosomes. Due to its dysfunction, cystine crystals accumulate in the lysosomes and ultimately cause apoptosis of the cell. Since cystinosin is ubiquitously present in the body, cystine crystals are deposited in every body structure and lead to the dysfunction of various organ systems in the course of time. Cystine crystals deposited in the cornea are a clinical hallmark of the disease, while there is less awareness of concomitant posterior segment alterations. Symmetrical pigment epithelial mottling and patches of depigmentation frequently start in the periphery and progress towards the posterior pole and can be encountered upon fundus biomicroscopy. Spectral-domain optical coherence tomography (SD-OCT) is an elegant tool for visualizing chorioretinal cystine crystals at the posterior pole. An SD-OCT-based clinical grading of the severity of the chorioretinal manifestation can potentially be applied as a biomarker for systemic disease status and for monitoring oral therapy adherence in the future. Along with previous histological examinations, it may also give information about the location of cystine crystals in the choroid and retina. This review aims to increase the awareness of vision-threatening retinal and choroidal changes in cystinosis and the concomitant findings in SD-OCT.

Spectral domain optical coherence tomography-based retinochoroidal cystine crystal score: a window into infantile nephropathic cystinosis

PRÉCIS: Cystinosis is a lysosomal storage disease leading to an accumulation of cystine crystals in several organs. We aim to comprehensively describe chorioretinal cystine crystals via spectral domain optical coherence tomography (SD-OCT) and elaborate a new biomarker for systemic disease control.

BACKGROUND/AIMS

Cystinosis is a rare lysosomal storage disease leading to an accumulation of cystine crystals in several organs. This study aims to describe the deposition of retinochoroidal crystals in infantile nephropathic cystinosis and to elucidate their potential value as an objective biomarker for systemic disease control.

METHODS

This cross-sectional study was carried out by the University Eye Hospital of the Ludwig-Maximilian University (Munich, Germany) in collaboration with the German Cystinosis Study Group. A complete ophthalmologic examination was performed, along with posterior segment SD-OCT (Spectralis; Heidelberg Engineering GmbH, Heidelberg, Germany). Retinochoroidal crystals were graded by employing a novel semiquantitative grading system-the retinochoroidal cystine crystal score (RCCCS). To quantify quality of vision, patients completed a specific questionnaire. A total of 85 eyes of 43 patients with cystinosis were included (mean age 22.3±8.8 years, range 6-39; male:female ratio=23:20).

RESULTS

Cystine crystals were detectable in all neuroretinal layers and the choroid, most frequently in the choriocapillaris. The RCCCS was negatively correlated with cysteamine intake (r=0.533, p=0.001) and positively with cystatin C, a stable parameter of renal function (r=0.496, p=0.016). Moreover, the value of the RCCCS affected subjective quality of vision. Genetic analysis indicated pronounced crystal deposition in patients with heterozygous mutations containing the 57-kb-deletion allele of the CTNS gene.

CONCLUSION

Ocular cystinosis leads to retinochoroidal crystal accumulation in every stage of the disease. Crystal deposition may be markedly influenced by oral cysteamine therapy. Therefore, the presented SD-OCT based grading system might serve as an objective biomarker for systemic disease control.

Hematopoietic Stem Cell Gene Therapy for Cystinosis: From Bench-to-Bedside

Cystinosis is an autosomal recessive metabolic disease that belongs to the family of lysosomal storage disorders. The gene involved is the CTNS gene that encodes cystinosin, a seven-transmembrane domain lysosomal protein, which is a proton-driven cystine transporter. Cystinosis is characterized by the lysosomal accumulation of cystine, a dimer of cysteine, in all the cells of the body leading to multi-organ failure, including the failure of the kidney, eye, thyroid, muscle, and pancreas, and eventually causing premature death in early adulthood. The current treatment is the drug cysteamine, which is onerous and expensive, and only delays the progression of the disease. Employing the mouse model of cystinosis, using Ctns-/- mice, we first showed that the transplantation of syngeneic wild-type murine hematopoietic stem and progenitor cells (HSPCs) led to abundant tissue integration of bone marrow-derived cells, a significant decrease in tissue cystine accumulation, and long-term kidney, eye and thyroid preservation. To translate this result to a potential human therapeutic treatment, given the risks of mortality and morbidity associated with allogeneic HSPC transplantation, we developed an autologous transplantation approach of HSPCs modified ex vivo using a self-inactivated lentiviral vector to introduce a functional version of the CTNS cDNA, pCCL-CTNS, and showed its efficacy in Ctns-/- mice. Based on these promising results, we held a pre-IND meeting with the Food and Drug Administration (FDA) to carry out the FDA agreed-upon pharmacological and toxicological studies for our therapeutic candidate, manufacturing development, production of the GMP lentiviral vector, design Phase 1/2 of the clinical trial, and filing of an IND application. Our IND was cleared by the FDA on 19 December 2018, to proceed to the clinical trial using CD34+ HSPCs from the G-CSF/plerixafor-mobilized peripheral blood stem cells of patients with cystinosis, modified by ex vivo transduction using the pCCL-CTNS vector (investigational product name: CTNS-RD-04). The clinical trial evaluated the safety and efficacy of CTNS-RD-04 and takes place at the University of California, San Diego (UCSD) and will include up to six patients affected with cystinosis. Following leukapheresis and cell manufacturing, the subjects undergo myeloablation before HSPC infusion. Patients also undergo comprehensive assessments before and after treatment to evaluate the impact of CTNS-RD-04 on the clinical outcomes and cystine and cystine crystal levels in the blood and tissues for 2 years. If successful, this treatment could be a one-time therapy that may eliminate or reduce renal deterioration as well as the long-term complications associated with cystinosis. In this review, we will describe the long path from bench-to-bedside for autologous HSPC gene therapy used to treat cystinosis.

Drug Repurposing for Rare Diseases: A Role for Academia

Background: The European Commission highlights in its Pharmaceutical Strategy the role of academic researchers in drug repurposing, especially in the development of orphan medicinal products (OMPs). This study summarizes the contribution of academia over the last 5 years to registered repurposed OMPs and describes barriers to success, based upon three real world cases.

Methods: OMPs granted marketing authorization between January 2016 and December 2020 were reviewed for repurposing and whether the idea originated from academia or industry. Three cases of drug repurposing were selected from different therapeutic areas and stages of development to identify obstacles to success.

Results: Thirteen of the 68 OMPs were the result of drug repurposing. In three OMPs, there were two developments such as both a new indication and a modified application. In total, twelve developments originated from academia and four from industry. The three cases showed as barriers to success: lack of outlook for sufficient return of investments (abatacept), lack of regulatory alignment and timing of interaction between healthcare professionals and regulators (etidronate), failure to register an old drug for a fair price, resulting in commercialization as a high priced orphan drug (mexiletine).

Conclusion: While the majority of repurposed OMPs originates in academia, a gap exists between healthcare professionals, regulators and industry. Future strategies should aim to overcome these hurdles leading to more patient benefit through sustainable access of repurposed drugs. Potential solutions include improved regulatory and reimbursement knowledge by academia and the right for regulators to integrate new effectiveness data into product labels.

Posterior segment optical coherence tomography findings in a case of nephropathic cystinosis

Cystinosis is a rare autosomal recessive lysosomal storage disorder characterized by abnormal accumulation of intracellular cystine in various tissues including the brain, kidneys, bones, and eyes. Infantile nephropathic cystinosis is the most severe phenotype of cystinosis that has been associated with a wide spectrum of ocular features. In this report, the author describes a posterior segment spectral-domain optical coherence tomography (SD-OCT) finding that has not been previously reported in a case of nephropathic cystinosis.

Examination of corneal deposits in nephropathic cystinosis using in vivo confocal microscopy and anterior segment optical coherence tomography: an age-dependent cross sectional study

Background

Presence of corneal cystine crystals is the main ocular manifestation of cystinosis, although controversial findings concerning the corneal layer with the highest density have been reported. The aim of this study was the analysis of the characteristics of crystal arrangement in different corneal layers and the assessment of corneal morphological changes with age.

Methods

A cross sectional study was carried out in three children and three adults who had nephropathic cystinosis and corneal cystine depositions. All patients underwent a comprehensive ophthalmological examination including best corrected distance visual acuity, slit-lamp examination, in vivo confocal microscopy and anterior segment optical coherence tomography. An evaluation of the depth of crystal deposits and crystal density in different corneal layers was also performed. Due to the low number of subjects no statistical comparison was performed.

Results

Anterior segment optical coherence tomography images revealed deposition of hyperreflective crystals from limbus to limbus in each patient. Crystals appeared as randomly oriented hyperreflective, elongated structures on in vivo confocal microscopy images in all corneal layers except the endothelium. In children the deposits occurred predominantly in the anterior stroma, while in adults, the crystals were mostly localized in the posterior corneal stroma with the depth of crystal deposition showing an increasing tendency with age (mean depth of crystal density was 353.17 ± 49.23 μm in children and it was 555.75 ± 25.27 μm in adults). Mean crystal density of the epithelium was 1.47 ± 1.17 (median: 1.5; interquartile range: 0.3–2.4). Mean crystal density of the anterior and posterior stroma of children and adults was 3.37 ± 0.34 (median: 3.4; interquartile range: 3.25–3.55) vs. 1.23 ± 0.23 (median: 1.2; interquartile range: 1.05–1.35) and 0.76 ± 0.49 (median: 0.7; interquartile range: 0.4–1.15) vs. 3.63 ± 0.29 (median: 3.7; interquartile range: 3.45–3.8), respectively. Endothelium had intact structure in all cases. Some hexagonal crystals were observed in two subjects.

Conclusions

In vivo confocal microscopy and anterior segment optical coherence tomography confirmed an age-related pattern of crystal deposition. In children, crystals tend to locate anteriorly, while in adults, deposits are found posteriorly in corneal stroma.

Using two smartphones to look for corneal cystine crystals

Cystinosis, a rare autosomal recessive lysosomal storage disease, can be difficult to detect. The most common form of the disease is infantile or nephropathic cystinosis. Crystals can accumulate in the eye as early as 1 year of age. Early recognition and prompt investigations prevent further accumulation of cystine and resultant end-organ injury. The disease is usually confirmed through biochemical and genetic testing, which can be time consuming. Looking for cystine corneal deposits remains an important diagnostic criterion and is the least invasive test to perform. It is recommended that ophthalmic manifestations of cystinosis be confirmed by an ophthalmologist. We describe the case of a 3-year-old girl who presented with worsening emesis, pyrexia, and lethargy, and was diagnosed with infantile cystinosis. This case is used to present a technique that can facilitate the preliminary search for corneal cystine crystals by using equipment as readily available as two smartphones. The technique may be easily used in a variety of settings, including hospitals, clinics, and primary care centers where there is delayed or difficult access to ophthalmologists.

The Ocular Status of Cystinosis Patients Receiving a Hospital Pharmacy-Made Preparation of Cysteamine Eye Drops: A Case Series

Introduction

Infantile nephropathic cystinosis (INC) is an autosomal recessive lysosomal disorder in which patients develop deposits of cystine crystals in their kidneys and corneas from a young age.

Methods

We conducted a retrospective analysis of children with INC seen by ophthalmologists at the Manchester Royal Eye Hospital between 2002 and 2018, to evaluate clinical findings, symptoms and treatment.

Results

Twenty-two children diagnosed with INC from age 0 (prenatally) to 11 years were assessed. All evaluable patients had corneal cystine crystal deposits, and 15 had mild to moderate photophobia. Ten patients had other ocular conditions including blepharitis/chalzion (n = 6), swollen optic nerve (n = 3), punctate epitheliopathy (n = 3), corneal scarring (n = 1),and elevated intraocular pressure (n = 2). Confocal imaging identified nerve abnormalities in two patients (enlarged corneal nerve + abnormal-looking tortuous nerves in one patient and beaded nerves in the sub-basal plexus in the other), both of whom had significant crystal deposition in the anterior stroma. Visual acuity was relatively unaffected. All 22 patients were receiving oral cysteamine, and 21 were applying cysteamine eye drops (galenic preparation of 0.55% concentration, compounded by a hospital pharmacy). Recommended application frequency was at least eight times per day in all patients with dosing information available.

Conclusions

This case series of patients with INC highlights the consistent pattern of corneal cystine crystal deposition, which is universally present from a young age in this condition, and the high incidence of photophobia even in young children. Corneal manifestations of INC persisted despite frequent administration of the hospital pharmacy-made eye drop preparation. Reasons for this lack of efficacy may include the lag period between diagnosis and first prescription of cysteamine eye drops and the difficulty in maintaining rigorous compliance with this treatment. In addition, the challenge for patients of maintaining optimal storage conditions may adversely affect the stability and efficacy of cysteamine within this preparation.

Funding

Editorial assistance was funded by Orphan Europe Ltd.

Nephropathic Cystinosis: Symptoms, Treatment, and Perspectives of a Systemic Disease

Cystinosis is a rare autosomal recessive lysosomal storage disorder caused by mutations in the CTNS gene. Main dysfunction is a defective clearance of cystine from lysosomes that leads to accumulation of cystine crystals in every tissue of the body. There are three different forms: infantile nephropathic cystinosis, which is the most common form, juvenile nephropatic, and non-nephropathic cystinosis. Mostly, first symptom in infantile nephropathic cystinosis is renal Fanconi syndrome that occurs within the first year of life. Another prominent symptom is photophobia due to corneal crystal deposition. Cystine depletion therapy with cysteamine delays end-stage renal failure but does not stop progression of the disease. A new cysteamine formulation with delayed-release simplifies the administration schedule but still does not cure cystinosis. Even long-term depletion treatment resulting in bypassing the defective lysosomal transporter cannot reverse Fanconi syndrome. A future perspective offering a curative therapy may be transplantation of CTNS-carrying stem cells that has successfully been performed in mice.

Clinical Practice: A Proposed Standardized Ophthalmological Assessment for Patients with Cystinosis

Cystinosis is a rare autosomal recessive disease with an incidence of approximately 1 case per 100,000–200,000 live births. Over the years, gaining in-depth knowledge of the disease has led to vast improvement in patient life expectancy. However, debilitating, extra-renal manifestations such as eye disease, in particular corneal crystal deposition and its associated photophobia, still occur frequently, regardless of patient age and notwithstanding the increased implementation of systemic therapy. Ophthalmological assessment has not yet been standardized. The aim of this article was to provide clear recommendations for ophthalmological assessment during follow-up of patients with cystinosis to improve quality and regularity of ophthalmological care and thereby minimize ophthalmological complications. A literature search was performed to assess previous and current recommendations on examinations to conduct during follow-up of patients with cystinosis. Multidisciplinary cystinosis clinics were set up in collaboration with the Department of Ophthalmology and the Department of Pediatric Nephrology to allow patients to be seen by a nephrologist, an ophthalmologist and other specialists on the same day. Based on the results of these multidisciplinary clinics the standardized clinical ophthalmological assessment was drafted. This is a protocol for follow-up, describing the approach taken regarding ophthalmological follow-up of patients with cystinosis, considering the different types of the disease and the time since diagnosis. Standard examination includes history, visual acuity, tonometry and slit-lamp examination, with fundus photography performed at diagnosis and annually thereafter. Confocal microscopy is the imaging modality of choice, while anterior segment optical coherence tomography (OCT) is a good alternative. Finally, posterior segment OCT for imaging of the macular region and optic nerve should be conducted on an annual basis.

The renal Fanconi syndrome in cystinosis: pathogenic insights and therapeutic perspectives

Cystinosis is an autosomal recessive metabolic disease that belongs to the family of lysosomal storage disorders. It is caused by a defect in the lysosomal cystine transporter, cystinosin, which results in an accumulation of cystine in all organs. Despite the ubiquitous expression of cystinosin, a renal Fanconi syndrome is often the first manifestation of cystinosis, usually presenting within the first year of life and characterized by the early and severe dysfunction of proximal tubule cells, highlighting the unique vulnerability of this cell type. The current therapy for cystinosis, cysteamine, facilitates lysosomal cystine clearance and greatly delays progression to kidney failure but is unable to correct the Fanconi syndrome. This Review summarizes decades of studies that have fostered a better understanding of the pathogenesis of the renal Fanconi syndrome associated with cystinosis. These studies have unraveled some of the early molecular changes that occur before the onset of tubular atrophy and identified a role for cystinosin beyond cystine transport, in endolysosomal trafficking and proteolysis, lysosomal clearance, autophagy and the regulation of energy balance. These studies have also led to the identification of new potential therapeutic targets and here, we outline the potential role of stem cell therapy for cystinosis and provide insights into the mechanism of haematopoietic stem cell-mediated kidney protection.

Treatment of Inherited Eye Defects by Systemic Hematopoietic Stem Cell Transplantation

PURPOSE

Cystinosis is caused by a deficiency in the lysosomal cystine transporter, cystinosin (CTNS gene), resulting in cystine crystal accumulation in tissues. In eyes, crystals accumulate in the cornea causing photophobia and eventually blindness. Hematopoietic stem progenitor cells (HSPCs) rescue the kidney in a mouse model of cystinosis. We investigated the potential for HSPC transplantation to treat corneal defects in cystinosis.

METHODS

We isolated HSPCs from transgenic DsRed mice and systemically transplanted irradiated Ctns-/- mice. A year posttransplantation, we investigated the fate and function of HSPCs by in vivo confocal and fluorescence microscopy (IVCM), quantitative RT-PCR (RT-qPCR), mass spectrometry, histology, and by measuring the IOP. To determine the mechanism by which HSPCs may rescue disease cells, we transplanted Ctns-/- mice with Ctns-/- DsRed HSPCs virally transduced to express functional CTNS-eGFP fusion protein.

RESULTS

We found that a single systemic transplantation of wild-type HSPCs prevented ocular pathology in the Ctns-/- mice. Engraftment-derived HSPCs were detected within the cornea, and also in the sclera, ciliary body, retina, choroid, and lens. Transplantation of HSPC led to substantial decreases in corneal cystine crystals, restoration of normal corneal thickness, and lowered IOP in mice with high levels of donor-derived cell engraftment. Finally, we found that HSPC-derived progeny differentiated into macrophages, which displayed tunneling nanotubes capable of transferring cystinosin-bearing lysosomes to diseased cells.

CONCLUSIONS

To our knowledge, this is the first demonstration that HSPCs can rescue hereditary corneal defects, and supports a new potential therapeutic strategy for treating ocular pathologies.

Treatment of corneal cystine crystal accumulation in patients with cystinosis

Cystinosis is a rare autosomal recessive disorder characterized by the accumulation of cystine within the cells of different organs. Infantile nephropathic cystinosis is the most common and severe phenotype. With the success of renal transplantation, these patients are now living longer and thus more long-term complications within different organs are becoming apparent. Ophthalmic manifestations range from corneal deposits of cystine crystals to pigmentary retinopathy. With increasing age, more severe ocular complications have been reported. Photophobia is a prominent symptom for patients. With prolonged survival and increasing age, this symptom, along with corneal erosions and blepharospasm, can become debilitating. This review revisits the basic pathogenesis of cystinosis, the ocular manifestations of the disease, and the treatment of corneal crystals.

A new gel formulation of topical cysteamine for the treatment of corneal cystine crystals in cystinosis: the Cystadrops OCT-1 study

OBJECTIVE

To establish the safety and efficacy of a new gel formulation of cysteamine hydrochloride (CH) eye drops, for the treatment of corneal complications of nephropathic cystinosis.

DESIGN

Open label dose response clinical trial.

PARTICIPANTS

Eight patients with infantile nephropathic cystinosis including 4 children, 3 adolescents, and 1 adult (mean age at inclusion, 12.1 ± 4.6 years) treated with CH 0.1% eye drops.

INTERVENTION

Patients were treated, in both eyes, with the control CH 0.1% eye drop formulation on average 4 times daily for one month and then switched to Cystadrops® at the same dose frequency. Based on clinical ocular findings, the dose regimen was adapted at D30 and D90 in order to decrease the frequency of instillation. After D90, this dose frequency was maintained, except in cases of crystal density worsening. Patients had a follow-up visit every 6 months during 48 months.

MAIN OUTCOME MEASURES

Safety assessment consisted of adverse event and serious adverse event monitoring and recording at each visit. For the efficacy study, the primary endpoint was the corneal cystine crystal density measured with an in vivo confocal microscopy (IVCM) score.

RESULTS

All patients completed the study. During the 4-year study period, neither serious adverse events nor significant adverse events related to the study drug were reported. After switching to Cystadrops®, the IVCM total score decreased from baseline to D90 by a mean of 28.6 ± 17.5% (p<0.001). From D90 to M48, the IVCM total score remained stable and significantly decreased as compared to that at D1 despite a reduced dose regimen from D90. At M48, the mean IVCM total score was 8.13 ± 4.15, decreased by a mean 29.9 ± 26.29% from D1 (p = 0.001), with a reduced number of instillations compared to that at D1. The IVCM total score and photophobia were significantly correlated (p = 0.04).

CONCLUSION

This study provides evidence that Cystadrops® gel is superior to the CH 0.1% formulation in terms of efficacy and has a good safety profile over a long follow-up period.

Crystalline-like keratopathy after intravenous immunoglobulin therapy with incomplete kawasaki disease: case report and literature review

A 7-year-old girl had presented with high body temperature and joint pain which continued for 3 days. Because of the prolonged history of unexplained fever, rash, bilateral nonpurulent conjunctival injection, oropharyngeal erythema, strawberry tongue, and extreme of age, incomplete Kawasaki disease was considered and started on an intravenous immunoglobulin infusion. Six days after this treatment, patient was referred to eye clinic with decreased vision and photophobia. Visual acuity was reduced to 20/40 in both eyes. Slit-lamp examination revealed bilateral diffuse corneal punctate epitheliopathy and anterior stromal haze. Corneal epitheliopathy seemed like crystal deposits. One day after presentation, mild anterior uveitis was added to clinical picture. All ocular findings disappeared in one week with topical steroid and unpreserved artificial tear drops. We present a case who was diagnosed as incomplete Kawasaki disease along with bilateral diffuse crystalline-like keratopathy. We supposed that unusual ocular presentation may be associated with intravenous immunoglobulin treatment.

Nephropathic cystinosis: late complications of a multisystemic disease

Cystinosis is a rare autosomal recessive disorder due to impaired transport of cystine out of cellular lysosomes. Its estimated incidence is 1 in 100,000 live births. End-stage renal disease (ESRD) is the most prominent feature of cystinosis and, along with dehydration and electrolyte imbalance due to renal tubular Fanconi syndrome, has accounted for the bulk of deaths from this disorder. Prior to renal transplantation and cystine-depleting therapy with cysteamine for children with nephropathic cystinosis, their lifespan was approximately 10 years. Now, cystinotic patients have survived through their fifth decade, but the unremitting accumulation of cystine has created significant non-renal morbidity and mortality. In this article we review the classic presentation of nephropathic cystinosis and the natural history, diagnosis, and treatment of the disorder's systemic involvement. We also emphasize the role of oral cysteamine therapy in preventing the late complications of cystinosis.

The ocular anomalies in a cystinosis animal model mimic disease pathogenesis

Cystinosis is a lysosomal storage disorder characterized by abnormal accumulation of cystine, which forms crystals at high concentrations. The causative gene CTNS encodes cystinosin, the lysosomal cystine transporter. The eye is one of the first organs affected (corneal lesions and photophobia in the first and visual impairment in the second decade of life). We characterized the ocular anomalies of Ctns-/- mice to determine whether they mimic those of patients. The most dramatic cystine accumulation was seen in the iris, ciliary body, and cornea of Ctns-/- mice. Consistently, Ctns-/- mice had a low intraocular pressure (IOP) and seemed mildly photophobic. Retinal cystine levels were elevated but increased less dramatically with age. Consistently, the retina was intact and electroretinogram (ERG) profiles were normal in mice younger than 19 mo; beyond this age, retinal crystals and lesions appeared. Finally, the lens contained the lowest cystine levels and crystals were not seen. The temporospatial pattern of cystine accumulation in Ctns-/- mice parallels that of patients and validates the mice as a model for the ocular anomalies of cystinosis. This work is a prerequisite step to the testing of novel ocular cystine-depleting therapies.

Ophthalmic manifestations and histopathology of infantile nephropathic cystinosis: report of a case and review of the literature

Cystinosis is a rare autosomal recessive metabolic disorder characterized by the intracellular accumulation of cystine, the disulfide of the amino acid cysteine, in many organs and tissues. Infantile nephropathic cystinosis is the most severe phenotype. Corneal crystal accumulation and pigmentary retinopathy were originally the most commonly described ophthalmic manifestations, but successful kidney transplantation significantly changed the natural history of the disease. As cystinosis patients now live longer, long-term complications in extrarenal tissues, including the eye, have become apparent. A case of an adult patient with infantile nephropathic cystinosis is reported. He presented with many long-term ocular complications of cystinosis. After 4 years of follow-up, the patient died from sepsis. Pathology of the phthisical eyes demonstrated numerous electron-transparent polygonal spaces, bounded by single membrane, in corneal cells, retinal pigment epithelial cells, and even choroidal endothelial cells. The ophthalmic manifestations and pathology of infantile nephropathic cystinosis are discussed and reviewed in light of the current report and other cases in the literature.

Nephropathic cystinosis: posterior segment manifestations and effects of cysteamine therapy

PURPOSE

Cystinosis is a rare autosomal recessive lysosomal storage disorder characterized by the intracellular accumulation of cystine. Treatment involves intracellular cystine depletion with oral cysteamine. A wide spectrum of ocular pathologic features has been associated with nephropathic cystinosis. We used the largest documented cohort of patients in the world to study the posterior segment manifestations associated with infantile nephropathic cystinosis and to determine retrospectively the effect of chronic oral cysteamine therapy on the frequency of these abnormalities.

DESIGN

Cross-sectional study of a series of patients.

PARTICIPANTS

Two hundred eight patients with infantile nephropathic cystinosis were studied at the National Institutes of Health between 1976 and 2004.

METHODS

All patients underwent an ophthalmic evaluation. Patients older than 11 years also underwent Humphrey static perimetry, and electrophysiological testing was performed when possible.

MAIN OUTCOME MEASURES

Visual acuity, retina findings, visual fields, and electroretinographic (ERG) findings.

RESULTS

Pigmentary changes with retinal pigment epithelial mottling, seen as early as infancy, were the most common posterior segment manifestations. Moderate to severe constriction of the visual fields, as well as moderate to severe reduction of rod- and cone-mediated ERG responses, was seen in older patients. The frequency of retinopathy correlated directly with time not receiving oral cysteamine therapy and inversely with time receiving oral cysteamine therapy.

CONCLUSIONS

Infantile nephropathic cystinosis has posterior segment complications that can contribute to significant visual handicap. Early initiation of oral cysteamine therapy can reduce the frequency of posterior segment complications in cystinosis patients.

Perioperative care of the patient with nephropathic cystinosis

Cystinosis is an autosomal recessive disease that results in a defective integral membrane protein responsible for the transport of cystine out of lysosomes. This results in the accumulation of cystine in the lysosomes of almost every tissue, with subsequent formation of damaging crystals. The cystinotic process may affect every system of the body, but is particularly damaging to the kidneys and eyes. We discuss the perioperative care of a cystinotic patient with renal insufficiency, Fanconi's syndrome, and photophobia. Other organ systems affected by the cystinotic process are also discussed, with suggestions for the perioperative management of each. Issues of primary concern during perioperative care include preservation of renal function and maintenance of fluid and electrolyte homeostasis.

Evolution of ocular manifestations in nephropathic cystinosis: a long-term study of a population treated with cysteamine

BACKGROUND

Nephropathic cystinosis is characterized by an accumulation of cystine crystals within most body tissues. Renal transplantation and oral cysteamine have improved the general prognosis of the disease, and ocular manifestations are now the most common complication. This long-term follow-up study describes the sequence of ocular manifestations in patients with nephropathic cystinosis treated with oral and topical cysteamine.

METHODS

Data were recorded for all patients with cystinosis examined between 1980 and 2000. For each patient, photophobia and visual acuity were evaluated and slit-lamp and fundus examinations were performed. For some patients, an electroretinogram was also performed.

RESULTS

Twenty-nine patients were observed during this period. They received oral and topical cysteamine. Photophobia and loss of visual acuity generally began by 10 years of age but were severe only after 15 years of age. Peripheral corneal epithelial infiltration appeared in the first few years of life. Infiltration evolved toward the depth and center of the cornea during the second decade of life. Retinopathy was present in 51.7% of the patients, with 3 cases of maculopathy and 3 cases of flattening on electroretinogram.

CONCLUSIONS

Photophobia and corneal infiltration, although generally severe after 15 years of age, could be treated with topical cysteamine and corneal transplantation. Retinal infiltration, previously described as frequent and potentially blinding, is currently observed in only half of these patients, with mild visual impairment. This could be related to the treatment with oral cysteamine reaching the retinal vascularization.

New aspects of the pathogenesis of cystinosis

Cystinosis is a lysosomal transport disorder characterized by an intra-lysosomal accumulation of cystine, the disulfide of the amino acid cysteine. It is the most common inherited cause of the renal Fanconi syndrome. There are various clinical forms, infantile, juvenile, and ocular, based on age of onset and severity of symptoms. The first clinical description appeared in the early 1900s, but it was not until 1998 that the causative gene, CTNS, was identified. CTNS encodes cystinosin, a novel seven transmembrane domain (TM) protein. Cystinosin is a lysosomal membrane protein that requires two lysosomal targeting signals: a classic GYDQL motif in its C-terminal tail and a novel conformational motif, the core of which is YFPQA, situated in the fifth inter-TM loop. Cystinosin is the lysosomal cystine transporter and its activity is H(+)-driven. A mouse model of cystinosis was recently generated and Ctns(-/-) mice accumulate cystine in all tissues. A high level of cystine accumulates in the kidney, but these mice do not present with proximal tubulopathy or renal dysfunction. The Ctns(-/-) mouse model may provide clues to the cause of the Fanconi syndrome associated with cystinosis, the origin of which remains poorly understood.

Intralysosomal cystine accumulation in mice lacking cystinosin, the protein defective in cystinosis

Cystinosis is an autosomal recessive disorder characterized by an accumulation of intralysosomal cystine. The causative gene, CTNS, encodes cystinosin, a seven-transmembrane-domain protein, which we recently showed to be a lysosomal cystine transporter. The most severe and frequent form of cystinosis, the infantile form, appears around 6 to 12 months, with a proximal tubulopathy (de Toni-Debré-Fanconi syndrome) and ocular damage. End-stage renal failure is reached by 10 years of age. Accumulation of cystine in all tissues eventually leads to multisystemic disease. Treatment with cysteamine, which reduces the concentration of intracellular cystine, delays disease progression but has undesirable side effects. We report the first Ctns knockout mouse model generated using a promoter trap approach. We replaced the last four Ctns exons by an internal ribosome entry site-betagal-neo cassette and showed that the truncated protein was mislocalized and nonfunctional. Ctns(-/-) mice accumulated cystine in all organs tested, and cystine crystals, pathognomonic of cystinosis, were observed. Ctns(-/-) mice developed ocular changes similar to those observed in affected individuals, bone defects and behavioral anomalies. Interestingly, Ctns(-/-) mice did not develop signs of a proximal tubulopathy, or renal failure. A preliminary therapeutic trial using an oral administration of cysteamine was carried out and demonstrated the efficiency of this treatment for cystine clearance in Ctns(-/-) mice. This animal model will prove an invaluable and unique tool for testing emerging therapeutics for cystinosis.

Infantile cystinosis presenting as chronic constipation

An infant presented with persistent constipation as the first clinical symptom of cystinosis before evidence of renal Fanconi's syndrome. The history of muscle weakness, failure to thrive, polydipsia, and polyuria prompted subsequent clinical and laboratory evaluations, leading to the correct diagnosis of cystinosis. Primary and persistent constipation as an initial manifestation of cystinosis has not been reported previously. Although rare, cystinosis should be considered in the differential diagnosis of constipation if other suggestive signs or symptoms are present.

Age-related prevalence of anterior segment complications in patients with infantile nephropathic cystinosis

PURPOSE

As a result of successful renal transplantation, patients with nephropathic cystinosis are now living into adulthood. As these patients age, anterior segment ocular complications, other than deposition of corneal crystals, become more evident. With our experience with 172 patients followed up at the National Institutes of Health between 1976 and 2000, the prevalence of anterior segment complications in nephropathic cystinosis was determined.

METHODS

A cross-sectional examination of age-specific prevalence was performed with logistic regression analysis of prevalence change with age.

RESULTS

Besides the corneal crystals apparent in all age groups, superficial punctate keratopathy, filamentary keratopathy, severe peripheral corneal neovascularization, band keratopathy, and posterior synechiae with iris thickening and transillumination were noted in the older age groups. The prevalence increased with age for each complication.

CONCLUSIONS

As patients with cystinosis grow older, more severe ophthalmic manifestations become evident. It remains to be seen how the prevalence of these complications will be altered by early initiation of oral and topical cysteamine therapy.

Cystinosis, cataract surgery, and corneal erosions

A 21-year-old man presented with severe corneal cystinosis and steroid-related cataract bilaterally. Rather than combined cataract surgery and penetrating keratoplasty, the patient had uneventful phacoemulsification and intraocular lens implantation after which visual acuity improved to 66 in both eyes. The outcome indicates that conventional phacoemulsification is sufficient in these cases. A guarded prognosis is advised in patients with cystinosis having cataract surgery as the fundal view is often impaired and there may be associated maculopathy.

Clinical polymorphism of cystinosis encephalopathy. Results of treatment with cysteamine

Of the 26 cystinotic patients over 19 years of age followed in our institution, 7 developed CNS complications at a mean age of 23 years. Two forms were observed. The first, associating cerebellar and pyramidal signs, mental deterioration and finally pseudo-bulbar palsy, may be called cystinosis encephalopathy. The other form resembled a stroke-like episode with coma and hemiplegia or milder symptoms. Hydrocephalus was rare and not associated with clinical symptoms in this series. Cysteamine was administered for longer than 6 months to 4 of the patients with encephalopathy. Two had an almost complete disappearance of their symptoms including the gross abnormalities of MR imaging in one; one improved partially and remained stable, and one continued to deteriorate but was suspected of non-compliance. These results suggest that cysteamine may be an effective treatment of cystinosis encephalopathy and encourage prescription of this drug in cystinosis in order to prevent this complication.

Update on nephropathic cystinosis

The cystine that accumulates within cystinotic lysosomes comes primarily from proteins which have been degraded within this organelle. The individual amino acids have specific transport mechanisms to exit the lysosome. The lysosomal cystine transporter is defective in all types of cystinosis. When cells from patients with nephropathic and benign cystinosis were fused, the defect was not corrected and the cystine level remained elevated. This strongly indicates that the genetic defects are allelic (i.e., on the same chromosome). Cysteamine is a weak base which enters the cystinotic lysosome and reacts with cysteamine. forming a mixed disulfide of half-cystine and cysteamine. This mixed disulfide rapidly exits the lysosome via the transport system for cationic amino acids which is normal in cystinosis. Because of the success of renal transplantation, many cystinosis patients are alive in their twenties and even early thirties. Unfortunately, these patients have developed damage to other organs including thyroid, eye, central nervous system, pancreas, and muscle. Cysteamine and its analog, phosphocysteamine, are very beneficial to cystinosis patients, especially when started early in life. These drugs may prevent the need for transplantation. It is too early to know if they will prevent damage to other organs.

The effect of topical cysteamine drops on reducing crystal formation within the cornea of patients affected by nephropathic cystinosis

We studied the usefulness of topical cysteamine ophthalmic drops in reducing crystal formation within the corneas of patients affected by nephropathic cystinosis. A dosage of 0.3% cysteamine given four times daily was chosen as a more manageable method than a previously reported protocol of hourly administration of 0.11% drops. No reduction in crystal formation was observed in our patients; they were followed for seven months.

Ocular changes in some progressive hereditary nephropathies

Ocular involvement is a common feature of three hereditary nephropathies: cystinosis, nephronophthisis and Alport's syndrome. The follow-up of 25 cases of infantile cystinosis over a period of 26 years demonstrated that the corneal and retinal epithelium were affected in the same way as the kidney epithelium. Corneal involvement induced photophobia and discomfort, but actual blindness was mainly due to retinal involvement, and therefore no corneal graft was performed. The use of topical cysteamine appears to be promising, but its production raises many questions so no definitive conclusions may be made. Since 1965, 51 patients with nephronophthisis have had ocular examinations; all patients had characteristic clinical symptoms and histological findings. The first group, which consisted of 18 children, all under 10 years of age, was found to have obvious chorioretinal degeneration. The second group, which consisted of 11 children, had a normal ocular examination and normal electroretinogram (ERG). The third group, consisting of 22 children, had a normal clinical examination but ERG tracings with variable alterations. In 28 instances of Alport's syndrome, two types of ocular abnormalities have been observed. In six cases, an anterior lenticonus was noted, which caused a major decline in visual acuity. Retinopathy, which did not affect vision, was observed in 13 cases.

Late symptoms in infantile cystinosis

Late symptoms of infantile cystinosis were evaluated in 19 patients aged 15-26 years who had a high graft survival following kidney transplantation. The end-stage cystinotic kidney was responsible for renal hypertension in 5 patients following grafts. Photophobia did not increase in relation to age, but 3 patients became blind and 1 lost the sight in one eye at 25 years of age. Two patients developed clinical symptoms of hypothyroidism, and 15 other patients had a compensated hypothyroidism. Four patients developed permanent insulin-dependent diabetes and 2 developed transient insulin-dependent diabetes after transplantation. The oral glucose tolerance test was abnormal in 11 of 14 patients on low-dose prednisone. Liver enlargement was noted in 10 cases, but only 3 patients developed clinical symptoms of portal hypertension. Symptoms of hypersplenism were observed in 6 cases leading to splenectomy. Repeat gross epistaxis was observed in 7 of the patients when on dialysis and persisted after transplantation in 1 patient, who died from nasal bleeding. A particular encephalopathy developed in 2 patients at the ages of 17 and 24, characterized by speech difficulties, pyramidal symptoms and cranial nerve deficit; one died at the age of 21. The mean adult height of these patients was 136.5 cm in males and 124 cm in females, and their psychosocial adjustment was related to the extra-renal complications of cystinosis rather than to the renal status.