Morphological changes and their associations with clinical parameters in children with nephropathic cystinosis and chronic kidney disease prior to kidney replacement therapy over 25 years.

BACKGROUND: Infantile nephropathic cystinosis (INC) is a rare lysosomal storage disorder, mostly and often firstly affecting the kidneys, together with impaired disharmonious growth and rickets, eventually resulting in progressive chronic kidney disease (CKD). With the introduction of cysteamine therapy, most pediatric patients reach adulthood with no need for kidney replacement therapy. Still, detailed changes in INC patients' clinical and morphological presentation over the past decades have not yet been thoroughly investigated. METHODS: Two groups with a respective total of 64 children with INC and 302 children with CKD, both treated conservatively and aged 2 to 18 years, were prospectively observed in the time span from 1998 to 2022 with 1186 combined annual clinical and morphological examinations clustered into two measurement periods (1998 to 2015 and ≥ 2016). RESULTS: In INC patients, thoracic proportion indices remained markedly increased, whereas body fat stores remained decreased over the past 25 years (+ 1 vs. below ± 0 z-score, respectively). Their CKD peers presented with overall improved growth, general harmonization of body proportions, and improved body fat stores, while INC patients only presented with an isolated significant increase in leg length over time (∆0.36 z-score). eGFR adjusted for age did not significantly change over the past 25 years in both groups. Alkaline phosphatase (ALP) showed a significant decrease in CKD patients over time, while remaining above normal levels in INC patients. CONCLUSIONS: Disproportionate thoracic shape and impaired body fat stores remain the most characteristic morphological traits in INC patients over the past 25 years, while causal mechanisms remain unclear.

Cortical impairment and reduced muscle mass in children and young adults with nephropathic cystinosis.

Nephropathic cystinosis is an orphan autosomal recessive lysosomal storage disease characterized by a deficiency of cystinosin, a cystine transporter protein, leading to tissue damage, primarily in the kidney and cornea. With the introduction of cystine-depleting therapy with cysteamine and the possibility to survive to adulthood, new challenges of skeletal complications are a concern, with sparse data available regarding bone development. The aim of the current study was to gain more information on bone density and geometry in these patients. Fifty-one patients (29 males, 22 females) with genetically-proven nephropathic cystinosis were clinically evaluated with a medical history, physical examination, grip strength measurements, biochemical and imaging studies. Bone mineral density, bone geometry and muscle cross sectional area were measured, and muscle was evaluated. Results were compared with age- and gender-specific reference data. Z-scores for height (mean [M] = -1.75, standard deviation [SD] = 1.43), weight (M = -1.67, SD = 1.29), and BMI (M = -0.98, SD = 1.29) were lower than reference data. Medullary cross-sectional area (CSA) and cortical density z-scores were not compromised (M = 0.12, SD = 1.56 and M = -0.25, SD = 1.63, respectively), but cortical CSA z-scores and Strength-Strain Index (SSI) were reduced (M = -2.16, SD = 1.08, M = -2.07, SD = 1.08). Muscular deficits were reflected by reduced z-scores for muscle CSA (M = -2.43, SD = 1.27) and grip strength (M = -3.01, SD = 1.10), along with jump force (34% lower than reference value). Multiple regression analyses indicated an association of muscle mass with medullary CSA and SSI, but not with cortical CSA. While bone density parameters were normal, bone geometry was altered, resulting in a thinner cortex with possible impact on bone strength. Muscle weakness be partially responsible for altered bone geometry and could provide a potential treatment target.

Nephropathic cystinosis is a rare lysosomal storage disease affecting primarily the kidney and cornea. With new treatment options patients survive to adulthood and challenges like bone development and fracture risk become a matter of concern. In this study we investigated bone density, bone geometry and muscle mass and function using peripheral quantitative computed tomography. We included 51 patients with genetically-proven cystinosis at an age between 6.6­39.6 years. Beside height impairment and low body weight patients had a thinner bone cortex leading to a reduced stress­strain index. This index represents the resistance of bone against torsional load and, therefore, is considered to be a good marker of bone strength: with low values fracture risk might increase. Further patients had lower muscle mass and muscle function, the latter evaluated by grip strength and jump force. Looking for the interaction of muscle and bone multiple regression analyses indicated an association of muscle mass with strength strain index. The muscle weakness might be partially responsible for altered bone geometry and lower bone strength and is possibly a treatment target, which has to be investigated in the future.

Chest configuration in children and adolescents with infantile nephropathic cystinosis compared with other chronic kidney disease entities and its clinical determinants.

BACKGROUND: Infantile nephropathic cystinosis (INC) is a systemic lysosomal storage disease causing intracellular cystine accumulation, resulting in renal Fanconi syndrome, progressive kidney disease (CKD), rickets, malnutrition, and myopathy. An INC-specific disproportionately diminished trunk length compared to leg length poses questions regarding the functionality of the trunk. METHODS: Thus, we prospectively investigated thoracic dimensions and proportions, as well as their clinical determinants in 44 pediatric patients with INC with CKD stages 1-5 and 97 age-matched patients with CKD of other etiology between the ages of 2-17 years. A total of 92 and 221 annual measurements of patients with INC and CKD, respectively, were performed, and associations between anthropometric and clinical parameters were assessed using linear mixed-effects models. RESULTS: Patients with INC exhibited altered chest dimensions that were distinct from CKD controls, characterized by markedly increased chest depth to height and chest depth to chest width ratio z-scores (> 1.0), while those of patients with CKD were only mildly affected (z-score within ± 1.0). Ratio z-scores differed significantly between both patient groups from 2-6 years of age onward. The degree of chest disproportion in INC patients was significantly associated with both the degree of CKD and tubular dysfunction (e.g., low serum phosphate and bicarbonate) across three different age groups (2-6, 7-12, and 13-17 years). CONCLUSION: Our data show an INC-specific alteration in thoracic shape from early childhood onward, which is distinct from CKD of other etiologies, suggesting early childhood subclinical changes of the musculoskeletal unit of the thoracic cage, which are associated with kidney function. A higher resolution version of the Graphical abstract is available as Supplementary information.

Health-related quality of life and patient-reported outcome measurements in patients with cystinosis.

Nephropathic cystinosis is a rare autosomal recessive lysosomal storage disorder. With the availability of treatment and renal replacement therapy, nephropathic cystinosis has evolved from an early fatal disease to a chronic, progressive disorder with potentially high impairment. We aim to review the literature on the health-related quality of life and identify appropriate patient-reported outcome measurements to assess the health-related quality of life of patients with cystinosis. For this review, we conducted a literature search in PubMed and Web of Science in September 2021. Inclusion and exclusion criteria for the selection of articles were defined a priori. We identified 668 unique articles through the search and screened them based on title and abstract. The full texts of 27 articles were assessed. Finally, we included five articles (published between 2009 and 2020) describing the health-related quality of life in patients with cystinosis. All studies, apart from one, were conducted in the United States, and no condition-specific measurement was used. Patients with cystinosis reported a lower health-related quality of life (for certain dimensions) than healthy subjects. Few published studies address the health-related quality of life of patients with cystinosis. Such data must be collected standardized and follow the FAIR (Findable, Accessible, Interoperable, and Reusable) principles. To gain a comprehensive understanding of the impact of this disorder on health-related quality of life, it is necessary to use generic and condition-specific instruments to measure this, preferably in large samples from longitudinal studies. A cystinosis-specific instrument for measuring health-related quality of life has yet to be developed.

Cystinosis. / Cystinose.

Cystinosis is a very rare autosomal recessive lysosomal storage disorder with an incidence of 1 : 150,000 - 1 : 200,000, and is caused by mutations in the CTNS gene encoding the lysosomal membrane protein cystinosin, which transports cystine out of the lysosome into the cytoplasm. As a result, accumulation of cystine occurs in almost all cells and tissues, especially in the kidneys, leading to multiple organ involvement. Introduction of drug therapy with cysteamine in the mid 1980s, along with the availability of renal replacement therapy in childhood, have dramatically improved patient outcome. Whereas patients used to die without therapy with end-stage renal failure during the first decade of life, nowadays most patients live well into adulthood without renal replacement therapy, and several reach 40 years. There is robust evidence that early initiation and sustained lifelong therapy with cysteamine are both essential for morbidity and mortality. The rarity of the disease and the multi-organ involvement present an enormous challenge for those affected and the providers of care for this patient group.

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.

Outcome of infantile nephropathic cystinosis depends on early intervention, not genotype: A multicenter sibling cohort study.

Infantile nephropathic cystinosis (INC) is an inheritable lysosomal storage disorder characterized by lysosomal cystine accumulation, progressive kidney disease, and multiple extrarenal complications (ERCs). Cysteamine postpones the onset of end-stage kidney disease (ESKD) and reduces the incidence of ERCs; however, cysteamine is generally initiated upon establishment of the renal Fanconi syndrome (FS) and partial loss of kidney function, whereas data on long-term effects of cysteamine administered from neonatal age are lacking. An international multicenter retrospective cohort study of siblings with INC was set up to investigate the outcome in relation to age at initiation of cysteamine versus CTNS genotype, with attention to patients treated with cysteamine from neonatal age. None of the siblings treated from neonatal age (n = 9; age 10 ± 6 years) had reached ESKD, while 22% of their index counterparts (n = 9; age 14 ± 5 years) had commenced renal replacement therapy. Siblings treated with cysteamine from the onset of symptoms at a younger age compared with their index counterparts, reached ESKD at a significant older age (13 ± 3 vs. 10 ± 3 years, p = 0.002). In contrast, no significant difference in ERCs was observed between sibling and index patients, independently from the age at initiation of cysteamine. The CTNS genotype had no impact on the overall outcome in this cohort. In INC, presymptomatic treatment with cysteamine results in a better renal outcome in comparison to treatment initiated from the onset of symptoms. This justifies including cystinosis into newborn screening programs. SYNOPSIS: In infantile nephropathic cystinosis, presymptomatic treatment with cysteamine improves the renal outcome which justifies the inclusion of cystinosis into newborn screening programs.

Beneficial effects of starting oral cysteamine treatment in the first 2 months of life on glomerular and tubular kidney function in infantile nephropathic cystinosis.

Nephropathic cystinosis is a rare lysosomal storage disease whose basic defect, impaired transport of cystine out of lysosomes, results in intracellular cystine storage. Affected individuals exhibit renal Fanconi Syndrome in infancy, end-stage kidney disease at approximately 10 years of age, and many other systemic complications. Oral cysteamine therapy mitigates the detrimental effects on glomerular function and prevents most of the late complications of the disease but has not shown benefit with respect to the early tubular damage of cystinosis. This is because cystinosis is generally diagnosed in the second year of life, after the damage to kidney tubular function has already occurred. We longitudinally evaluated 6 infants diagnosed and treated with cysteamine from before 2 months of age. The 4 infants with good compliance with cysteamine and consistently low leucocyte cystine levels maintained normal eGFR values, exhibited only minor degrees of renal Fanconi Syndrome, and maintained normal serum levels of potassium, bicarbonate, phosphate, and calcium without electrolyte or mineral supplementation through 2, 4, 10 and 16 years of age. Thus, renal Fanconi syndrome can be attenuated by early administration of cysteamine and renew the call for molecular-based newborn screening for cystinosis.

Relationship between age at initiation of cysteamine treatment, adherence with therapy, and glomerular kidney function in infantile nephropathic cystinosis.

Infantile nephropathic cystinosis, due to impaired transport of cystine out of lysosomes, occurs with an incidence of 1 in 100-200,000 live births. It is characterized by renal Fanconi syndrome in the first year of life and glomerular dysfunction progression to end-stage kidney disease by approximately 10 years of age. Treatment with oral cysteamine therapy helps preserve glomerular function, but affected individuals eventually require kidney replacement therapy. This is because glomerular damage had already occurred by the time a child is diagnosed with cystinosis, typically in the second year of life. We performed a retrospective multicenter study to investigate the impact of initiating cysteamine treatment within the first 2 months of life in some infants and comparing two different levels of adherence in patients diagnosed at the typical age. We collected 3983 data points from 55 patients born between 1997 and 2020; 52 patients with 1592 data points could be further evaluated. These data were first analyzed by dividing the patient cohort into three groups: (i) standard treatment start with good adherence, (ii) standard treatment start with less good adherence, and (iii) early treatment start. At every age, mean estimated glomerular filtration rate (eGFR) was higher in early-treated patients than in later-treated patients. Second, a generalized additive mixed model (GAMM) was applied showing that patients with initiation of treatment before 2 months of age are expected to have a 34 ml/min/1.73 m2 higher eGFR than patients with later treatment start while controlling for adherence and patients' age. These data strongly suggest that oral cysteamine treatment initiated within 2 months of birth preserves kidney function in infantile nephropathic cystinosis and provide evidence of the utility of newborn screening for this disease.

Patients With Infantile Nephropathic Cystinosis in Germany and Austria: A Retrospective Cohort Study.

Background: Infantile nephropathic cystinosis (INC) is a rare lysosomal storage disorder resulting in progressive chronic kidney disease (CKD) and a variety of extrarenal manifestations. This orphan disease remains a challenge for patients, their families and health care providers. There is currently no comprehensive study on patients' clinical course in Germany and Austria. Methods: A retrospective cohort study including 74 patients at eleven centers of care was conducted. Data on time of diagnosis, CKD stage, leukocyte cystine levels (LCL), extrarenal manifestations, and treatment was collected from medical charts and subsequently analyzed using explorative statistics. Age at initiation of kidney replacement therapy (KRT) was evaluated by Kaplan-Meier analyses for different groups of patients. Results: Patients were diagnosed at a median age of 15 months (IQR: 10-29, range: 0-110), more recent year of birth was not associated with earlier diagnosis. Oral cystine-depleting therapy (i.e., cysteamine) was prescribed at a median dose of 1.26 g/m2 per day (IQR: 1.03-1.48, range: 0.22-1.99). 69.2% of all 198 LCL measurements of 67 patients were within the desired target range (≤ 1 nmol cystine/mg protein). Median time-averaged LCLs per patient (n = 65) amounted to 0.57 nmol cystine/mg protein (IQR: 0.33-0.98, range: 0.07-3.13) when considering only values at least 1 year after initiation of therapy. The overall median height of 242 measurements of 68 patients was at the 7th percentile (IQR: 1-25, range: 1-99). 40.5% of the values were ≤ the 3rd percentile. Patient sex and year of birth were not associated with age at initiation of KRT, but patients diagnosed before the age of 18 months required KRT significantly later than those patients diagnosed at the age of ≥ 18 months (p = 0.033): median renal survival was 21 years (95% CI: 16, -) vs. 13 years (95% CI, 10, -), respectively. Conclusion: Early diagnosis and initiation of cystine depleting therapy is important for renal survival in children with INC. Cysteamine doses and LCL showed that treatment in this cohort met international standards although there is great interindividual variety. Patient growth and other aspects of the disease should be managed more effectively in the future.

Newborn Screening: Review of its Impact for Cystinosis.

Newborn screening (NBS) programmes are considered to be one of the most successful secondary prevention measures in childhood to prevent or reduce morbidity and/or mortality via early disease identification and subsequent initiation of therapy. However, while many rare diseases can now be detected at an early stage using appropriate diagnostics, the introduction of a new target disease requires a detailed analysis of the entire screening process, including a robust scientific background, analytics, information technology, and logistics. In addition, ethics, financing, and the required medical measures need to be considered to allow the benefits of screening to be evaluated at a higher level than its potential harm. Infantile nephropathic cystinosis (INC) is a very rare lysosomal metabolic disorder. With the introduction of cysteamine therapy in the early 1980s and the possibility of renal replacement therapy in infancy, patients with cystinosis can now reach adulthood. Early diagnosis of cystinosis remains important as this enables initiation of cysteamine at the earliest opportunity to support renal and patient survival. Using molecular technologies, the feasibility of screening for cystinosis has been demonstrated in a pilot project. This review aims to provide insight into NBS and discuss its importance for nephropathic cystinosis using molecular technologies.

Body growth, upper arm fat area, and clinical parameters in children with nephropathic cystinosis compared with other pediatric chronic kidney disease entities.

Children with infantile nephropathic cystinosis (INC), an inherited lysosomal storage disease resulting in cystine accumulation in all body cells, are prone to progressive chronic kidney disease (CKD), impaired growth and reduced weight gain; however, systematic anthropometric analyses are lacking. In this prospective multicenter study we investigated linear growth, body proportion, body mass index (BMI), upper arm fat area (UFA) and biochemical parameters in 43 pediatric INC patients with CKD stages 1 to 5 and 49 age-matched CKD controls, with 193 annual measurements. INC patients showed more impaired height than CKD controls (-1.8 vs -0.7 z-score; P < .001), despite adequate cysteamine therapy, treatment for Fanconi syndrome and more frequent use of growth hormone. Only the youngest INC patients shared the same body pattern with CKD controls characterized by preferential impairment of leg length and rather preserved trunk length. In late-prepuberty, body pattern changed only in INC patients due to improved leg growth and more impaired trunk length. Mean UFA z-score in INC patients was slightly reduced in early childhood and progressively decreased thereafter reaching -0.8 z-score in adolescence, while CKD controls showed a steady increase in standardized BMI and UFA especially during adolescent age. Menarche in female INC patients was significantly delayed compared to CKD controls. Our data indicate that with age and progression of disease, pediatric INC patients undergo unique changes of body growth and fat stores that are distinct from those with CKD stemming from other causes, suggesting other factors apart from CKD to contribute to this development. Pediatric patients with infantile nephropathic cystinosis display more severe impaired linear growth than other peer CKD patients, despite of cysteamine treatment, supplementation for Fanconi syndrome, and more frequent use of growth hormone, with a distinct change of body proportions and overall lower body fat.

Neuromuscular conditions and the impact of cystine-depleting therapy in infantile nephropathic cystinosis: A cross-sectional analysis of 55 patients.

Infantile nephropathic cystinosis (INC) is a rare lysosomal storage disease caused by biallelic mutations in the cystinosin gene, leading to cystine accumulation in various organs. The aim of this cross-sectional study was to investigate neuromuscular complications in a cohort of 55 patients (aged 2.8-41.3 years, median 18.5 years) with INC. Clinical examination, jumping mechanography, clinical neurophysiology, and muscle/nerve ultrasound were performed. Physical performance, measured by mechanography, was below average in all patients. However, this reduction in physical performance was not always detected by conventional muscle power assessment. Twenty-eight percent of patients had mostly mild axial weakness of the neck flexors and/or of the abdominal rectus muscles, the latter often presenting during childhood. One adult patient had generalized muscle weakness. Two patients had evidence of specific neuromuscular conditions, which may not have been directly related to cystinosis. 30% of patients presented with mild, 7% with moderate, and 5% with severe weakness of the intrinsic muscles of the hand. Muscle wasting was more pronounced in the older cystinosis patients with multiple organ complications. Sonographic increase in muscle echogenicity corresponded only with severe weakness. Electromyography of the intrinsic hand muscles, performed in selected patients, showed myopathic, neurogenic, or mixed myopathic-neurogenic abnormalities. A particularly important finding of this study is that the neuromuscular complications were largely independent from both the age of initiation of pharmacological cystine-depleting therapy and from adherence to treatment. Significant correlation was observed between better physical performance in jumping and cysteine levels in leukocytes.

An international cohort study spanning five decades assessed outcomes of nephropathic cystinosis.

Nephropathic cystinosis is a rare disease secondary to recessive mutations of the CTNS gene encoding the lysosomal cystine transporter cystinosin, causing accumulation of cystine in multiple organs. Over the years, the disease has evolved from being a fatal condition during early childhood into a treatable condition, with patients surviving into adulthood. Data on cystinosis are limited by the rarity of the disease. Here, we have investigated factors associated with kidney and growth outcome in a very large cohort of 453 patients born between 1964 and 2016 and followed in Belgium, Germany, Austria, France, Italy, Spain, The Netherlands, Turkey and United Kingdom. From the 1970s to the 1990s, the median increase in kidney survival was 9.1 years. During these years, cysteamine, a cystine-depleting agent, was introduced for the treatment of cystinosis. Significant risk factors associated with early progression to end-stage kidney disease assessed by Cox proportional multivariable analysis included delayed initiation of cysteamine therapy and higher mean leucocyte cystine levels. No significant effect on kidney function was observed for gender, pathogenic variant of the CTNS gene, and the prescription of indomethacin or renin angiotensin system blockers. Significantly improved linear growth was associated with early use of cysteamine and lower leukocyte cystine levels. Thus, our study provides strong evidence in favor of early diagnosis and optimization of cystine depletion therapy in nephropathic cystinosis.

A Medical Report Feature for OSSE Rare Disease Registries.

Web-based patient registries support clinicians by providing a way to effectively store and process data. Here, we present a new feature for the open-source registry software OSSE: medical reports generated with R Markdown. As part of a rare disease research project, we describe the process from requirements assessment to the current state of technical implementation. The feature offers clinicians the possibility to download customised as well as generic reports from an OSSE rare disease registry.

Establishing an objective biomarker for corneal cystinosis using a threshold-based Spectral domain optical coherence tomography imaging algorithm.

PURPOSE: The purpose of the present study was to establish a semi-automated threshold-based image segmentation algorithm to detect and objectively quantify corneal cystine crystal deposition in ocular cystinosis with anterior segment optical coherence tomography (AS-OCT). METHODS: This prospective, observational, comparative study included 88 eyes of 45 patients from the German Cystinosis Registry Study as well as 68 eyes of 35 healthy control subjects. All eyes were imaged with AS-OCT (Cirrus HD-OCT 5000, Carl Zeiss Meditec AG, Jena, Germany). As an initial step, B-scan images were subjectively analysed for typical changes in morphology in comparison to healthy controls. Based on the experience gained, an objective semi-automated B-scan image segmentation algorithm was developed using a grey scale value-based threshold method to automatically quantify corneal crystals. RESULTS: On AS-OCT B-scans, corneal crystals appeared as hyperreflective deposits within the corneal stroma. The crystals were distributed either in all stromal layers (43 eyes, 49%) or confined to the anterior (23 eyes, 26%) or posterior stroma (22 eyes, 25%), respectively. The novel automatic B-scan image segmentation algorithm was most efficient in delineating corneal crystals at higher grey scale thresholds (e.g. 226 of a maximum of 255). Significant differences in suprathreshold grey scale pixels were observable between cystinosis patients and healthy controls (p < 0.001). In addition, the algorithm was able to detect an age-dependent depth distribution profile of crystal deposition. CONCLUSION: Objective quantification of corneal cystine crystal deposition is feasible with AS-OCT and can serve as a novel biomarker for ocular disease control and topical treatment monitoring.

Bone and Mineral Metabolism in Children with Nephropathic Cystinosis Compared with other CKD Entities.

CONTEXT: Children with nephropathic cystinosis (NC) show persistent hypophosphatemia, due to Fanconi syndrome, as well as mineral and bone disorders related to chronic kidney disease (CKD); however, systematic analyses are lacking. OBJECTIVE: To compare biochemical parameters of bone and mineral metabolism between children with NC and controls across all stages of CKD. DESIGN: Cross-sectional multicenter study. SETTING: Hospital clinics. PATIENTS: Forty-nine children with NC, 80 CKD controls of the same age and CKD stage. MAIN OUTCOME MEASURES: Fibroblast growth factor 23 (FGF23), soluble Klotho, bone alkaline phosphatase (BAP), tartrate-resistant acid phosphatase 5b (TRAP5b), sclerostin, osteoprotegerin (OPG), biochemical parameters related to mineral metabolism, and skeletal comorbidity. RESULTS: Despite Fanconi syndrome medication, NC patients showed an 11-fold increased risk of short stature, bone deformities, and/or requirement for skeletal surgery compared with CKD controls. This was associated with a higher frequency of risk factors such as hypophosphatemia, hypocalcemia, low parathyroid hormone (PTH), metabolic acidosis, and a specific CKD stage-dependent pattern of bone marker alterations. Pretransplant NC patients in mild to moderate CKD showed a delayed increase or lacked an increase in FGF23 and sclerostin, and increased BAP, TRAP5b, and OPG concentrations compared with CKD controls. Post-transplant, BAP and OPG returned to normal, TRAP5b further increased, whereas FGF23 and PTH were less elevated compared with CKD controls and associated with higher serum phosphate. CONCLUSIONS: Patients with NC show more severe skeletal comorbidity associated with distinct CKD stage-dependent alterations of bone metabolism than CKD controls, suggesting impaired mineralization and increased bone resorption, which is only partially normalized after renal transplantation.

Chitotriosidase as a Novel Biomarker for Therapeutic Monitoring of Nephropathic Cystinosis.

BACKGROUND: Nephropathic cystinosis, a hereditary lysosomal storage disorder caused by dysfunction of the lysosomal cotransporter cystinosin, leads to cystine accumulation and cellular damage in various organs, particularly in the kidney. Close therapeutic monitoring of cysteamine, the only available disease-modifying treatment, is recommended. White blood cell cystine concentration is the current gold standard for therapeutic monitoring, but the assay is technically demanding and is available only on a limited basis. Because macrophage-mediated inflammation plays an important role in the pathogenesis of cystinosis, biomarkers of macrophage activation could have potential for the therapeutic monitoring of cystinosis. METHODS: We conducted a 2-year prospective, longitudinal study in which 61 patients with cystinosis who were receiving cysteamine therapy were recruited from three European reference centers. Each regular care visit included measuring four biomarkers of macrophage activation: IL-1ß, IL-6, IL-18, and chitotriosidase enzyme activity. RESULTS: A multivariate linear regression analysis of the longitudinal data for 57 analyzable patients found chitotriosidase enzyme activity and IL-6 to be significant independent predictors for white blood cell cystine levels in patients of all ages with cystinosis; a receiver operating characteristic analysis ranked chitotriosidase as superior to IL-6 in distinguishing good from poor therapeutic control (on the basis of white blood cell cystine levels of <2 nmol 1/2 cystine/mg protein or ≥2 nmol 1/2 cystine/mg protein, respectively). Moreover, in patients with at least one extrarenal complication, chitotriosidase significantly correlated with the number of extrarenal complications and was superior to white blood cell cystine levels in predicting the presence of multiple extrarenal complications. CONCLUSIONS: Chitotriosidase enzyme activity holds promise as a biomarker for use in therapeutic monitoring of nephropathic cystinosis.