Accumulation Of Cystine In Lysosomes Research Articles

Ocular cystinosis – Clinical presentation and review of the literature

Cystinosis is one of the rarest multisystem lysosomal storage disorders characterized by the accumulation of cystine in lysosomes due to a defective CTNS gene. Infantile nephropathic cystinosis (INC) is the most common and severe phenotype. Varied ocular manifestations have been described in the literature, but few are rarely reported. We are documenting those rare findings in three children who were referred from the Pediatric department. As the disease presents with typical ocular features, they can be used as the diagnostic criteria expediting the time of diagnosis and early institution of therapy and this series highlights this fact.

Enteric-Coated Cysteamine Bitartrate in Cystinosis Patients.

Cystinosis is a severe inherited metabolic storage disease caused by the lysosomal accumulation of cystine. Lifelong therapy with the drug cysteamine bitartrate is necessary. Cysteamine cleaves intralysosomal cystine, and thereafter, it can exit from the organelle. The need for frequent dosing every 6 h and the high prevalence of gastrointestinal side effects lead to poor therapy adherence. The purpose of our study was to improve cysteamine treatment by comparing the efficacy of two cysteamine formulas. This is highly relevant for the long-term outcome of cystinosis patients. The cystine and cysteamine levels of 17 patients taking immediate-release cysteamine (IR-cysteamine/Cystagon®) and 6 patients taking encapsulated delayed-release cysteamine (EC-cysteamine) were analyzed. The EC-cysteamine levels showed a near-ideal pharmacokinetic profile indicative of delayed release (longer Tmax and Tmin), and the corresponding cystine levels showed few fluctuations. In addition, the Cmax of IR-cysteamine was greater, which was responsible for unbearable side effects (e.g., nausea, vomiting, halitosis, lethargy). Treatment with EC-cysteamine improves the quality of life of cystinosis patients because the frequency of intake can be reduced to 2-3 times daily and it has a more favorable pharmacokinetic profile than IR-cysteamine. In particular, cystinosis patients with no access to the only approved delayed-release cysteamine Procysbi® could benefit from a cost-effective alternative.

Nephropathic cystinosis in Poland: a 40-year retrospective study.

Nephropathic cystinosis (NC) is a rare, autosomal recessive disorder leading to lysosomal accumulation of cystine. It is caused by mutations in the CTNS gene encoding a cystine cotransporter cystinosin. The infantile (INC) and juvenile (JNC) forms are distinguished. The former, responsible for 95% of cases, is characterized by development of renal Fanconi syndrome, end-stage kidney disease (ESKD), and extrarenal complications. A therapy with cysteamine significantly improves outcomes. There are limited data on NC in the Central Eastern European countries. We aimed to evaluate the prevalence, genetic background, and clinical course of NC in the Polish population. We performed a retrospective analysis of data of all identified NC patients in Poland. Between 1982 and 2017, 15 patients with NC (13 ICN, 2 JCN) were identified. The most common mutations of the CTNS gene were c.18_c.21delGACT and c.681+1G>A, whereas only 2 patients carried the 57 kb deletion. The majority (11/13) of INC patients with limited access to the cysteamine therapy developed ESKD at a median age of 11 years and 9 of them received kidney transplants. Three INC patients died at a median age of 24 years. In contrast, 2 INC patients treated adequately present normal kidney function and growth at the age of 13 and 11 years. Two JNC patients presented a milder course. The prevalence of NC in Poland is much lower than in the Western countries and its molecular background appears to be different. The unfavorable course in the majority of INC patients was caused by a limited access to the cysteamine treatment.

POS-090 CYSTINOSIS: A RARE BUT TREATABLE CAUSE OF PROXIMAL RENAL TUBULAR ACIDOSIS

Cystinosis is a rare lysosomal storage disorder which is characterized by defective cystine transporter and accumulation of cystine in lysosomes of cells of various body organs. Most common and severe presentation is in infancy as Fanconi syndrome (infantile nephropathic cystinosis). Incidence of cystinosis is 1 in 1 to 2 lakh newborns; with high incidence in Europe and UK. In India total 19 cases are registered with Cystinosis Society of India. The most common reported Indian mutation is p. Ser141Phe in contrast to 57Kb deletion affecting first 10 exons of CTNS which is commonly reported in Europe. We report a 23 months old male child of Indian origin, born out of non-consanguineous marriage, who presented with acute gastroenteritis and seizure. On examination, child had severe dehydration, pallor, signs of rickets, failure to thrive and polyuria even in the state of dehydration. Initial evaluation revealed a S. creatinine 2.62mg/dl. After fluid resuscitation renal functions improved (nadir S. creatinine 0.82mg/dl). As per mother the child had increased frequency of urination since age of 7 months with history of hospitalization twice for dehydration and dyselectrolytemia at the age of 8 months and 10 months. During follow up period, child had persistent hyperchloremic metabolic acidosis and low serum phosphate.Urine analysis revealed- proteinuria (2+, 100mg/dl), glycosuria (sugar 1+ , 100mg/dl) and phosphaturia. Urinary anion gap was positive; Urine chromatography was suggestive of generalized aminoaciduria. Ultrasound abdomen was normal. On the basis of above findings, the diagnosis of proximal renal tubular acidosis was made. Eye evaluation was suggestive of fine crystals deposition in cornea. In view of possibility of cystinosis, Genetic analysis by next generation sequencing was done which confirmed novel mutation in cystinosine gene (NM_001031681.2: c.771_793delGGGACCACGTGGCTGCAGT;p.Gly258SerfsTer30). Child was started treatment with cysteamine capsules and eyedrops along with bicarbonate, vitamin D, calcium and phosphorus supplements. On treatment child started gaining height and weight, urine output decreased and S. creatinine continued to be at nadir value of 0.8 mg/dl. Renal tubular acidosis may be just a clinical presentation of an underlying systemic disorder, therefore relevant clinical examination with need based molecular testing should be done. As early diagnosis forms the key to specific therapy for long term favorable outcome.

Bioengineered Cystinotic Kidney Tubules Recapitulate a Nephropathic Phenotype.

Nephropathic cystinosis is a rare and severe disease caused by disruptions in the CTNS gene. Cystinosis is characterized by lysosomal cystine accumulation, vesicle trafficking impairment, oxidative stress, and apoptosis. Additionally, cystinotic patients exhibit weakening and leakage of the proximal tubular segment of the nephrons, leading to renal Fanconi syndrome and kidney failure early in life. Current in vitro cystinotic models cannot recapitulate all clinical features of the disease which limits their translational value. Therefore, the development of novel, complex in vitro models that better mimic the disease and exhibit characteristics not compatible with 2-dimensional cell culture is of crucial importance for novel therapies development. In this study, we developed a 3-dimensional bioengineered model of nephropathic cystinosis by culturing conditionally immortalized proximal tubule epithelial cells (ciPTECs) on hollow fiber membranes (HFM). Cystinotic kidney tubules showed lysosomal cystine accumulation, increased autophagy and vesicle trafficking deterioration, the impairment of several metabolic pathways, and the disruption of the epithelial monolayer tightness as compared to control kidney tubules. In particular, the loss of monolayer organization and leakage could be mimicked with the use of the cystinotic kidney tubules, which has not been possible before, using the standard 2-dimensional cell culture. Overall, bioengineered cystinotic kidney tubules recapitulate better the nephropathic phenotype at a molecular, structural, and functional proximal tubule level compared to 2-dimensional cell cultures.

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.

Human and animal fertility studies in cystinosis reveal signs of obstructive azoospermia, an altered blood‐testis barrier and a subtherapeutic effect of cysteamine in testis

Cystinosis is an inherited metabolic disorder caused by autosomal recessive mutations in the CTNS gene leading to lysosomal cystine accumulation. The disease primarily affects the kidneys followed by extra‐renal organ involvement later in life. Azoospermia is one of the unclarified complications which are not improved by cysteamine, which is the only available disease‐modifying treatment. We aimed at unraveling the origin of azoospermia in cysteamine‐treated cystinosis by confirming or excluding an obstructive factor, and investigating the effect of cysteamine on fertility in the Ctns −/− mouse model compared with wild type. Azoospermia was present in the vast majority of infantile type cystinosis patients. While spermatogenesis was intact, an enlarged caput epididymis and reduced levels of seminal markers for obstruction neutral α‐glucosidase (NAG) and extracellular matrix protein 1 (ECM1) pointed towards an epididymal obstruction. Histopathological examination in human and mouse testis revealed a disturbed blood‐testis barrier characterized by an altered zonula occludens‐1 (ZO‐1) protein expression. Animal studies ruled out a negative effect of cysteamine on fertility, but showed that cystine accumulation in the testis is irresponsive to regular cysteamine treatment. We conclude that the azoospermia in infantile cystinosis is due to an obstruction related to epididymal dysfunction, irrespective of the severity of an evolving primary hypogonadism. Regular cysteamine treatment does not affect fertility but has subtherapeutic effects on cystine accumulation in testis.

A comparison of immediate release and delayed release cysteamine in 17 patients with nephropathic cystinosis

BackgroundNephropathic cystinosis is a rare and severe metabolic disease leading to an accumulation of cystine in lysosomes which especially harms kidney function. A lifelong therapy with the aminothiol cysteamine can delay the development of end-stage renal disease and the necessity of kidney transplantation. The purpose of our study was to compare the effectiveness of immediate-release and delayed-release cysteamine on cystine and cysteamine levels as well as assessing the onset of adverse effects.MethodsWe retrospectively analysed cystine and cysteamine levels of 17 patients after a single dose of immediate-release cysteamine (Cystagon®, Mylan Pharmaceuticals, Canonsburg, PA and Recordati Pharma GmbH) as well as a single dose of delayed-release cysteamine (Procysbi®; Horizon Pharma USA and Chiesi Farmaceutici S.p.A., Parma, Italy) respectively. Data were collected during a period of three years in the context of optimizing the individual treatment regimens. The dose of DR-cysteamine was reduced to 70% of the equivalent dose of IR-cysteamine. The efficacy of both formulas in depleting white blood cells’ cystine levels and their side effects were compared.ResultsImmediate (IR)- and delayed-release (DR) cysteamine effectively decreased intracellular cystine levels under the target value of 0.5 nmol cystine/mg protein, while fewer side effects occurred under DR-cysteamine. Mean maximum levels of cysteamine were reached after 60 min with IR-cysteamine and after 180 min with DR-cysteamine.ConclusionA therapy with DR-cysteamine is as effective as IR-cysteamine while less side effects were reported. Our data show that DR-cysteamine should be dosed higher than 70% of the equivalent dose of IR-cysteamine in order to decrease cystine levels over an extended period of time. Moreover, our data suggest increasing the dosing scheme of Procysbi® to three times daily, to prevent a rapid decrease and achieve a steadier decline in cystine levels. Due to the more convenient dosing scheme, DR-cysteamine might ameliorate therapy adherence and improve patients’ quality of life.

Renal and Extra Renal Manifestations in Adult Zebrafish Model of Cystinosis.

Cystinosis is a rare, incurable, autosomal recessive disease caused by mutations in the CTNS gene. This gene encodes the lysosomal cystine transporter cystinosin, leading to lysosomal cystine accumulation in all cells of the body, with kidneys being the first affected organs. The current treatment with cysteamine decreases cystine accumulation, but does not reverse the proximal tubular dysfunction, glomerular injury or loss of renal function. In our previous study, we have developed a zebrafish model of cystinosis through a nonsense mutation in the CTNS gene and have shown that zebrafish larvae recapitulate the kidney phenotype described in humans. In the current study, we characterized the adult cystinosis zebrafish model and evaluated the long-term effects of the disease on kidney and extra renal organs through biochemical, histological, fertility and locomotor activity studies. We found that the adult cystinosis zebrafish presents cystine accumulation in various organs, altered kidney morphology, impaired skin pigmentation, decreased fertility, altered locomotor activity and ocular anomalies. Overall, our data indicate that the adult cystinosis zebrafish model reproduces several human phenotypes of cystinosis and may be useful for studying pathophysiology and long-term effects of novel therapies.

Cysteamine-bicalutamide combination therapy corrects proximal tubule phenotype in cystinosis.

Nephropathic cystinosis is a severe monogenic kidney disorder caused by mutations in CTNS, encoding the lysosomal transporter cystinosin, resulting in lysosomal cystine accumulation. The sole treatment, cysteamine, slows down the disease progression, but does not correct the established renal proximal tubulopathy. Here, we developed a new therapeutic strategy by applying omics to expand our knowledge on the complexity of the disease and prioritize drug targets in cystinosis. We identified alpha‐ketoglutarate as a potential metabolite to bridge cystinosin loss to autophagy, apoptosis and kidney proximal tubule impairment in cystinosis. This insight combined with a drug screen revealed a bicalutamide–cysteamine combination treatment as a novel dual‐target pharmacological approach for the phenotypical correction of cystinotic kidney proximal tubule cells, patient‐derived kidney tubuloids and cystinotic zebrafish.

Serum Chitotriosidase level as a Novel Biomarker for Therapeutic Monitoring of Nephropathic Cystinosis among the Iraqi children

Background: Cystinosis is a rare autosomal recessive lysosomal storage disease with high morbidity and mortality. It is caused by mutations in the CTNS gene that encodes the cystine transporter, cystinosin, which leads to lysosomal cystine accumulation. It is the major cause of inherited Fanconi syndrome, and should be suspected in young children with failure to thrive and signs of renal proximal tubular damage. The diagnosis can be missed in infants, because not all signs of renal Fanconi syndrome are present during the first months of life. Elevated white blood cell cystine content is the cornerstone of the diagnosis. Since chitotriosidase (CHIT1 or chitinase-1) is mainly produced by activated macrophages both in normal and inflammatory conditions which suggest that cystinosis should be included within the differential diagnosis of disorders associated with increased plasma chitotriosidase activity. This study is aimed to estimate serum chitotriosidase level, as a screening marker and therapeutic monitor for cystinosis disease in Iraqi children with cystinosis.Subjects and Methods: The present study is a case-control study that included samples of 30 children with nephropathic cystinosis, compared to 25 healthy control children from those attending at The Genetic Rare Diseases Center / AL-Emamain AL-Kadhimain Teaching Hospital, Baghdad-Iraq.Results: Our results reported that cystinotic children had a marked elevation of serum chitotriosidase activity, compared to age-matched healthy children, besides a significant associated with leukocyte-cystine content for cystinotic patients.CHT1 as a Novel BiomarkerConclusion: Estimation of serum chitotriosidase activity might aid in monitoring the therapeutic benefits of cysteamine therapy, as well as the prognosis of the disease when WBC cystine assessment is not available.Key Words: Cystinosis, Cysteamine, Chitotriosidase.

Testicular function in males with infantile nephropathic cystinosis.

STUDY QUESTIONDo males with the rare lysosomal storage disease infantile nephropathic cystinosis (INC) have a chance of biological fatherhood?SUMMARY ANSWERCryostorage of semen could be an option for approximately 20% of young males with INC, with surgical sperm retrieval from the centre of the testes providing additional opportunities for fatherhood.WHAT IS KNOWN ALREADYBiallelic mutations in the cystinosin (CTNS) gene in INC cause dysfunction in cystine transport across lysosomal membranes and cystine accumulation throughout the body. Spontaneous paternity in cystinosis has not been described, despite the availability of cysteamine treatment. Azoospermia has been diagnosed in small case series of males with INC. ART using ICSI requires few spermatozoa, either from semen or extracted surgically from the testes of azoospermic men. However, there is limited evidence to suggest this could be successful in INC.STUDY DESIGN, SIZE, DURATIONIn this prospective cohort study performed between 2018 and 2019, we performed a cross-sectional investigation of 18 male patients with INC to delineate endocrine and spermatogenic testicular function.PARTICIPANTS/MATERIALS, SETTING, METHODSSerum hormone levels, semen samples (according to World Health Organization 2010 standards), and testicular ultrasound images were analysed in 18 male patients aged 15.4–40.5 years. Surgical sperm extraction was performed in two, and their testicular biopsies were investigated by light and electron microscopy. Past adherence to cysteamine treatment was assessed from medical record information, using a composite scoring system.MAIN RESULTS AND THE ROLE OF CHANCEAdherence to cysteamine treatment was high in most patients. Testicular volumes and testosterone levels were in the normal ranges, with the exception of two and three older patients, respectively. Serum LH levels were above the normal range in all subjects aged ≥20 years. FSH levels were elevated in all but four males: three with spermatozoa in semen and one adolescent. Inhibin B levels were shown to be lower in older men. Testicular ultrasound revealed signs of obstruction in 67% of patients. Reduced fructose and zinc seminal markers were found in 33%, including two patients with azoospermia who underwent successful surgical sperm retrieval. Histology identified fully preserved spermatogenesis in the centre of their testes, but also tubular atrophy and lysosomal overload in Sertoli and Leydig cells of the testicular periphery.LIMITATIONS, REASONS FOR CAUTIONLimitations of this study are the small number of assessed patients and the heterogeneity of their dysfunction in cystine transport across lysosomal membranes.WIDER IMPLICATIONS OF THE FINDINGSThis study suggests that testicular degeneration in cystinosis results from the lysosomal overload of Sertoli and Leydig cells of the testicular periphery, and that this can possibly be delayed, but not prevented, by good adherence to cysteamine treatment. Endocrine testicular function in INC may remain compensated until the fourth decade of life; however, azoospermia may occur during adolescence. Cryostorage of semen could be an option for approximately 20% of young males with INC, with surgical sperm retrieval providing additional opportunities for biological fatherhood.STUDY FUNDING/COMPETING INTEREST(S)This work was supported by the Cystinosis Foundation Germany. The authors have no competing interests to declare.TRIAL REGISTRATION NUMBERn/a.

MFSD12 mediates the import of cysteine into melanosomes and lysosomes.

Dozens of genes contribute to the vast variation in human pigmentation. Many of these encode proteins that localize to the melanosome, the lysosome-related organelle that synthesizes pigment, but have unclear functions 1,2. Here, we describe the MelanoIP method for rapidly isolating melanosomes and profiling their labile metabolite contents. We use it to study MFSD12, a transmembrane protein of unknown molecular function that when suppressed causes darker pigmentation in mice and humans 3,4. We find that MFSD12 is required to maintain normal levels of cystine, the oxidized dimer of cysteine, in melanosomes, and to produce cysteinyldopas, the precursors of pheomelanin synthesis made in melanosomes via cysteine oxidation 5,6. Tracing and biochemical analyses show that MFSD12 is necessary for the import of cysteine into melanosomes, and, in non-pigmented cells, lysosomes. Indeed, loss of MFSD12 reduced the accumulation of cystine in lysosomes of fibroblasts from patients with cystinosis, a lysosomal storage disease caused by inactivation of the lysosomal cystine exporter CTNS (Cystinosin)7–9. Thus, MFSD12 is an essential component of the long-sought cysteine importer for melanosomes and lysosomes.

Impact of Age at Starting Cysteamine Therapy on Serum Chitotriosidase in Cystinotic Iraqi Children

Cystinosis is a rare autosomal recessive lysosomal storage disease with high morbidity and mortality. Itis caused by mutations in the CTNS gene that encodes the cystine transporter, cystinosin, which leadsto lysosomal cystine accumulation. It is the major cause of inherited Fanconi syndrome and should besuspected in young children with failure to thrive and signs of renal proximal tubular damage. The diagnosiscan be missed in infants, because not all signs of renal Fanconi syndrome are present during the first monthsof life. Elevated white blood cell cystine content is the corner stone for the diagnosis. Since chitotriosidase(CHIT1 or chitinase-1) is mainly produced by activated macrophages both in normal and inflammatoryconditions. Which suggests that cystinosis should be included in the differential diagnosis of disorders withincreased plasma chitotriosidase activity. This study is aimed to investigate the impact of cystinosis on therenal function in relation to age at detection and initiation of treatment course,besides estimating serumchitotriosidase level,as a screening marker and therapeutic monitor for cystinosis disease in Iraqi childrenwith cystinosis.The present study is a case-control study included a samples of 30 children with nephropathic cystinosis,compared to 25 healthy control children from those attending at The Genetic Rare Diseases Center/ALEmamain AL-Kadhimain teaching hospital, Baghdad-Iraq.Our results report patients who started taking the medication (cysteamine) before two years of age werepresented with significantly lower levels of cystine and chitotriosidase in addition to better renal function(higher GFR) (P-value = 0.0001) .In other words, earlier treatment led to better disease control and lessdeterioration of renal function.In conclusion serum chitotriosidase activity estimation might aid in monitoring therapeutic benefit ofcysteamine therapy and the prognosis of the disease when WBC cystine assessment is not available.

Cell-Based Phenotypic Drug Screening Identifies Luteolin as Candidate Therapeutic for Nephropathic Cystinosis.

Mutations in the gene that encodes the lysosomal cystine transporter cystinosin cause the lysosomal storage disease cystinosis. Defective cystine transport leads to intralysosomal accumulation and crystallization of cystine. The most severe phenotype, nephropathic cystinosis, manifests during the first months of life, as renal Fanconi syndrome. The cystine-depleting agent cysteamine significantly delays symptoms, but it cannot prevent progression to ESKD and does not treat Fanconi syndrome. This suggests the involvement of pathways in nephropathic cystinosis that are unrelated to lysosomal cystine accumulation. Recent data indicate that one such potential pathway, lysosome-mediated degradation of autophagy cargoes, is compromised in cystinosis. To identify drugs that reduce levels of the autophagy-related protein p62/SQSTM1 in cystinotic proximal tubular epithelial cells, we performed a high-throughput screening on the basis of an in-cell ELISA assay. We then tested a promising candidate in cells derived from patients with, and mouse models of, cystinosis, and in preclinical studies in cystinotic zebrafish. Of 46 compounds identified as reducing p62/SQSTM1 levels in cystinotic cells, we selected luteolin on the basis of its efficacy, safety profile, and similarity to genistein, which we previously showed to ameliorate other lysosomal abnormalities of cystinotic cells. Our data show that luteolin improves the autophagy-lysosome degradative pathway, is a powerful antioxidant, and has antiapoptotic properties. Moreover, luteolin stimulates endocytosis and improves the expression of the endocytic receptor megalin. Our data show that luteolin improves defective pathways of cystinosis and has a good safety profile, and thus has potential as a treatment for nephropathic cystinosis and other renal lysosomal storage diseases.

P0075EXPERT OPINION ON THE MULTIDISCIPLINARY MANAGEMENT OF CYSTINOSIS IN ADOLESCENT AND ADULT PATIENTS

Abstract Background and Aims Cystinosis is a rare autosomal recessive lysosomal storage disorder caused by mutations in the CTNS gene on chromosome 17p13. It affects between 1:150,000–1:200,000 live births, with a prevalence of approximately 1.6 per million. It is a life-long progressive disease which results in an abnormal lysosomal accumulation of the amino acid cystine in multiple organs and tissues of the body. The most common presentation of cystinosis (95%) is the infantile nephropathic form, with renal symptoms developing in the first few months of life. Over the next 10–20 years, extra-renal manifestations of cystinosis become apparent, which require multidisciplinary care. Here we describe a consensus-based programme with the objective of creating clinical recommendations to support HCPs with the management of adolescents and adults living with the multi-organ effects of cystinosis. Method The programme was led by a Steering Committee (SC) of European clinicians with expertise in managing cystinosis. Recommendations were developed using a quasi-Delphi methodology. The SC identified and prioritised a list of key questions. An Extended Faculty (EF) of additional specialists with extensive experience managing cystinosis in patients of all ages, were invited to answer the questions via an online digital platform. The consolidated answers of expert opinion were summarised into recommendations that were supported by evidence-based guidance and additional published data where possible. The EF were invited to agree / disagree with the draft clinical recommendations. Where there was disagreement, the SC members amended the recommendations and the EF re-voted on the revisions. This process continued until consensus was achieved on all final recommendations. Results The expert-agreed clinical recommendations reflect the multi-organ effects of cystinosis. Thus, advice on factors relating to the nervous system, muscle involvement, ophthalmology, cardio-respiratory system, dental care and nutrition, dermatology, endocrine system, and gastrointestinal and hepatological involvement, are given, along with renal considerations. Guidance on fertility and family planning that reflect some of the major advances in recent years, are also provided. Ideas on improving psychological well-being and adherence includes recommendations on the use of validated screening tests, increasing access to occupational therapy, and interacting with patient groups. The programme has also produced an online checklist to support HCPs in their daily clinical practice by providing a focus to guide regular consultations with the patient. Conclusion These expert recommendations offer HCPs relevant advice that support them in the management of adolescents and adults living with the multi-organ effects of cystinosis. The recommendations complement existing international and local guidance and aim to improve patient outcomes.

Bone Disease in Nephropathic Cystinosis: Beyond Renal Osteodystrophy.

Patients with chronic kidney disease (CKD) display significant mineral and bone disorders (CKD-MBD) that induce significant cardiovascular, growth and bone comorbidities. Nephropathic cystinosis is an inherited metabolic disorder caused by the lysosomal accumulation of cystine due to mutations in the CTNS gene encoding cystinosin, and leads to end-stage renal disease within the second decade. The cornerstone of management relies on cysteamine therapy to decrease lysosomal cystine accumulation in target organs. However, despite cysteamine therapy, patients display severe bone symptoms, and the concept of “cystinosis metabolic bone disease” is currently emerging. Even though its exact pathophysiology remains unclear, at least five distinct but complementary entities can explain bone impairment in addition to CKD-MBD: long-term consequences of renal Fanconi syndrome, malnutrition and copper deficiency, hormonal disturbances, myopathy, and intrinsic/iatrogenic bone defects. Direct effects of both CTNS mutation and cysteamine on osteoblasts and osteoclasts are described. Thus, the main objective of this manuscript is not only to provide a clinical update on bone disease in cystinosis, but also to summarize the current experimental evidence demonstrating a functional impairment of bone cells in this disease and to discuss new working hypotheses that deserve future research in the field.

LC-MS/MS measurement of leukocyte cystine; effect of preanalytic factors

Cystinosis is an autosomal recessive disorder characterized by the accumulation of cystine in lysosomes, causing irreversible damage to organs, especially the kidneys. Intracellular leukocyte cystine concentrations are used to diagnose cystinosis and to monitor cysteamine treatment. The aim of this study was to develop and validate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method without derivatization capable of measuring leukocyte intracellular cystine concentrations.During development, the effects of using three different protein precipitation agents were evaluated in terms of sensitivity and the matrix effect, with 12% trichloroacetic acid providing the highest sensitivity. The effects of different blood collection tubes were also assessed in terms of recovery, matrix effect, and protein content. Compared to other methods, our method was quicker (run time of 3 min), was linear over the range 0.078–100 μM, and had lower limits of detection (0.0192 μM) and quantification (0.0582 μM). The intra-day and inter-day reproducibility %CVs were ≤10%. and the method had excellent recovery rates (94%–106%). Other parameters including matrix selectivity, injection carryover, leukocyte lysate stability were also validated and met the acceptance criterias of European Medicines Agency (EMA) Guideline. The assay was successfully applied to quantify cystine leukocyte concentration in healthy and cystinosis patients.

CTNS\xa0mRNA molecular analysis revealed a novel mutation in a child with infantile nephropathic cystinosis: a case report

BackgroundCystinosis is an autosomal recessive lysosomal storage disorder characterized by accumulation of cystine in lysosomes throughout the body. Cystinosis is caused by mutations in the CTNS gene that encodes the lysosomal cystine carrier protein cystinosin. CTNS mutations result in either complete absence or reduced cystine transporting function of the protein. The diagnosis of nephropathic cystinosis is generally based on measuring leukocyte cystine level, demonstration of corneal cystine crystals by the slit lamp examination and confirmed by genetic analysis of the CTNS gene.Case presentationA boy born to consanguineous Caucasian parents had the characteristic clinical features of the infantile nephropathic cystinosis including renal Fanconi syndrome (polydipsia/polyuria, metabolic acidosis, hypokalemia, hypophosphatemia, low molecular weight proteinuria, glycosuria, cystine crystals in the cornea) and elevated WBC cystine levels. Initially we performed RFLP analysis of the common in the Northern European population 57-kb deletion of proband’s DNA, then a direct Sanger sequencing which revealed no mutations in the coding part of the CTNS gene. To confirm the diagnosis we performed RT-PCR analysis of total RNA obtained from patient-derived fibroblasts in combination with cDNA sequencing. This revealed the skipping of exon 4 and exon 5 in the CTNS in our patient. Therefore, we detected a novel 9-kb homozygous deletion in the CTNS gene at genomic DNA level, spanning region from intron 3 to intron 5. In order to identify the inheritance pattern of the deletion we analyzed DNA of proband’s mother and father. Both parents were found to be heterozygous carriers of the CTNS mutation.ConclusionsAnalysis of CTNS gene transcript allowed to identify a large homozygous deletion in the patient with infantile nephropathic cystinosis. Mutational detection at RNA level may be an efficient tool to establish the genetic defect in some cystinosis patients.

Visual and verbal learning and memory in cystinosis

Cystinosis is a rare genetic lysosomal storage disorder characterized by the accumulation of cystine in lysosomes. Many organ systems are vulnerable to this cystine accumulation including the CNS. A past study demonstrated that children with cystinosis have deficits in visual learning and memory while their verbal learning and memory and global intellectual function are spared (Spilkin, Ballantyne, & Trauner, 2009). However, no related study has been performed to assess the dissociation between visual and verbal learning and memory in adults with cystinosis who have had the benefit of longterm treatment with the cystine-depleting agent, cysteamine. In this study we assessed visual and verbal learning and memory in 15 adults with cystinosis, with a mean age of 30.2 years. The results indicate that adults with cystinosis have no significant deficits in either verbal or visual learning and memory. However, the individuals did perform better on the verbal assessment. The results suggest that if early and continued treatment is given to individuals with cystinosis there is a relative sparing of visual learning and memory that might have otherwise declined. This emphasizes the essential nature of the proper clinical management of cystinosis.