57-kb Deletion Research Articles

#2245 ECYSCO, a European cystinosis cohort

Abstract Background and Aims Cystinosis is a rare multisystem lysosomal storage disease due to variants in the CTNS gene, coding for the carrier protein cystinosin, a lysosome membrane transporter, causing cystine accumulation. Specific treatment by cysteamine decreases renal and extrarenal complications frequency in cystinosis patients but data on long-term manifestations of the disease are lacking. The aim of the ECYSCO cohort is to describe the natural history of the disease and the effect of treatments. Methods We set up a European, multi-centre, longitudinal, non-interventional cohort, ECYSCO, that uses observational study methods to collect uniform data. 243 patients with a confirmed diagnosis of cystinosis and followed in 25 French and 5 European centers (Belgium, Italy, Spain and Germany) were included. Data are collected on the secure RaDiCo platform, via an e-CRF (REDCap). Results Data from 177 patients (50.8% male) were analyzed. Median age at diagnosis was 1.3 years [IQ 0.9; 1.8], with earlier diagnosis since the 1980s, but no further improvement in the 2000s. Genetic analysis was available for 158 patients: 46 (31.9%) presented with homozygous 57kb deletion in the CTNS gene, 57 (39.6%) with heterozygous 57kb deletion associated with another variant and 46 (26.4%) with other variants. The type of variant had no impact on the age at diagnosis. Median age at cysteamine start was 1.6 years (IQ 1.0-3.0). An improvement on age at treatment start was observed after the 1990s. All but 7 patients were treated with cysteamine. Sixty-seven patients received immediate release formulation (Cystagon®) and 103 received extended release formulation (Procysbi®). Median white blood cell cystine level was 1.2 nmol ½ cystine/mg protein (IQ 0.6; 2.2). The median duration of treatment was 21.5 years [IQ 11.7; 31.1]. 165 (93,2%) patients also received cysteamine ocular gel, Cystadrops®. Median age at inclusion was 18.4 years (IQ 10.4; 30.6). At that time, 104 patients (57.8%) had reached kidney failure (KF). There was no impact of genotype on age at KF. Median age at KF was 12.9 years [IQ 9.9; 18.0]. A 5-year gain in renal survival was observed after the 1990s. 102 patients (56.7%) received a kidney transplant. Among these transplanted patients: 76 (74.5%) received 1 transplant, 23 (22.5%) received 2 consecutive transplants, and 3 (2.9%) received 3. Median eGFR in the remaining patients was 58.9 ml/min [IQ 40.4; 82.2]. Extrarenal manifestations included hypothyroidism in 29 (16.4%) patients, diabetes mellitus in 15 (8.4%), skeletal manifestations in 89 (53.6%), myopathy in 28 (17.9%), and neurological disorders in 21 (13.5%). Skeletal manifestations involved patients before dialysis/transplantation in 46% of cases. The main complications in these patients were genu valgum (62.9%), genu varum (11.1%), kyphosis (21.2%), fractures (20.4%), and 12.6% required surgery. Patients with myopathy were dialysed or transplanted in 58.8% of cases. Conclusion Cystinosis is a good example of a pediatric disease with multiorgan involvement extending into adult care. More than half of patients are adults and have reached kidney failure even if age at renal replacement therapy start has increased. The high frequency of extra-renal manifestations demonstrates the importance of a multidisciplinary follow up of these patients.

#4432 ECYSCO: A EUROPEAN COHORT DEDICATED TO CYSTINOSIS

Abstract Background and Aims Cystinosis is a rare multisystem lysosomal storage disease due to variants in the CTNS gene, coding for the carrier protein cystinosine, a lysosome membrane transporter causing cystine accumulation with a reported incidence of 1:180,000 live births. Specific treatment by cysteamine decreases renal and extrarenal complications frequency and increases life expectancy. Recently, new treatments for cystinosis entered into the European market with an extended-release formulation of cysteamine and a new formulation of eye drops. The aim of this project is to describe the natural history of the disease and long-term clinical manifestations. Method We set up a European, multi-centre, longitudinal, non-interventional cohort, ECYSCO, that uses observational study methods to collect uniform data. 243 patients with a confirmed diagnosis of cystinosis and followed in 25 French and 5 European centers (Belgium, Italy, Spain and Germany) were included. Data are collected on the secure RaDiCo platform, via an e-CRF (REDCap). Results Data from 180 patients (50.0% male) were analyzed. Median age at diagnosis was 1.3 years [IQ 0.8; 1.9], with earlier diagnosis since the 1980s, but no further improvement in the 2000s. Genetic analysis was available for 174 patients: 57 (32.8%) presented with homozygous 57kb deletion in the CTNS gene, 71 (40.8%) with heterozygous 57kb deletion associated with another variant and 46 (26.4%) with other variants. The type of variant had no impact on the age at diagnosis. Median age at cysteamine start was 1,6 years (IQ 1.0-3.0). An improvement on age at treatment start was observed after the 1990s. All but 6 patients were treated with cysteamine. 71 patients received immediate release formulation (Cystagon®) and 103 received extended release formulation (Procysbi®). Median white blood cell cystine level was correct at 1.2 nmol ½ cystine/mg protein (IQ 0.59; 2.20). The median duration of treatment was 21.5 years [IQ 11.7; 31.1]. 167 (95,9%) patients also received cysteamine ocular gel, Cystadrops®. Median age at inclusion was 19.08 years (IQ 10.43; 31.41). At that time, 104 patients (57.8%) had reached end-stage renal disease (ESRD). There was no impact of genotype on age at ESRD. Median age at ESRD was 12.9 years [IQ 9.9; 18.0]. A 5-year gain in renal survival was observed after the 1990s. 102 patients (56.7%) received a kidney transplant. Among these transplanted patients: 76 (74.5%) received 1 transplant, 23 (22.5%) received 2 consecutive transplants, and 3 (2.9%) received 3. Median eGFR in the remaining patients was 58.9 ml/min [IQ 40.4; 82.2]. Extrarenal manifestations included hypothyroidism in 61 (33.9%) patients, diabetes mellitus in 11 (6.1%), skeletal manifestations in 73 (40.5%), myopathy in 32 (17.8%), and neurological disorders in 22 (12.2%). At inclusion, 36 patients had no ESRD and no extra-renal complication. Conclusion Cystinosis is a good example of a pediatric disease with multiorgan involvement extending into adult care. More than half of patients are adults and have reached ESRD even if age at renal replacement therapy start has increased. The high frequency of extra-renal manifestations demonstrates the importance of a multidisciplinary follow up of these patients.

Molecular characterization of CTNSmutations in Tunisian patients with ocular cystinosis.

BackgroundOcular cystinosis is a rare autosomal recessive disorder characterized by intralysosomal cystine accumulation in renal, ophthalmic (cornea, conjunctiva), and other organ abnormalities. Patients with ocular cystinosis are mostly asymptomatic and typically experience mild photophobia due to cystine crystals in the cornea observed accidently during a routine ocular examination. The ocular cystinosis is associated with different mutations in CTNS gene. Cysteamine therapy mostly corrects the organ abnormalities.MethodsThis study was performed in collaboration with the department of ophthalmology of Farhat Hached Hospital. The Optical Coherence Tomography (OCT) of the cornea and retinal photography were used to search cystine crystals within the corneas and conjunctiva in eight Tunisian patients. Screening for the common 57-kb deletion was performed by standard multiplex PCR, followed by direct sequencing of the entire CTNS gene.ResultsThe studied patients were found to have cystine crystal limited anterior corneal stroma and the conjunctiva associated with retinal crystals accumulation. CTNS gene sequencing disclosed 7 mutations: three missense mutations (G308R, p.Q88K, and p.S139Y); one duplication (C.829dup), one framshift mutation (p.G258f), one splice site mutation (c.681 + 7delC) and a large deletion (20,327-bp deletion). Crystallographic structure analysis suggests that the novel mutation p.S139Y is buried in a first transmembrane helix closed to the lipid bilayer polar region, introducing a difference in hydrophobicity which could affect the hydrophobic interactions with the membrane lipids. The second novel mutation p.Q88K which is located in the lysosomal lumen close to the lipid membrane polar head region, introduced a basic amino acid in a region which tolerate only uncharged residue. The third missense mutation introduces a positive change in nonpolar tail region of the phospholipid bilayer membrane affecting the folding and stability of the protein in the lipid bilayer.ConclusionsOur data demonstrate that impaired transport of cystine out of lysosomes is the most common, which is obviously associated with the mutations of transmembrane domains of cystinosine resulting from a total loss of its activity.

Clinical and genetic characteristics of Tunisian children with infantile nephropathic cystinosis.

Nephropathic cystinosis is an autosomal recessive disease caused by a mutation in the CTNS gene which encodes cystinosin, a lysosomal cystine transporter. The spectrum of mutations in the CTNS gene is not well defined in the North African population. Here, we investigated twelve patients with nephropathic cystinosis belonging to eight Tunisian families in order to analyze the clinical and genetic characteristics of Tunisian children with infantile nephropathic cystinosis. Clinical data were collected retrospectively. Molecular analysis of the CTNS gene was performed by Sanger sequencing. We describe a new splicing mutation c.971-1G > C in the homozygous state in 6/12 patients which seems to be a founder mutation. The reported deletion of 23nt c.771_793 Del (p.Gly258Serfs*30) was detected in a homozygous state in one patient and in a heterozygous compound state with the c.971-1G > C mutation in 3/12 patients. Two of 12 patients have a deletion of exons 4 and 5 of the CTNS gene. None of our patients had the most common 57-kb deletion. The mutational spectrum in the Tunisian population is different from previously described populations. Thus, a molecular diagnostic strategy must be implemented in Tunisia, by targeting as a priority the common mutations described in this country. Such a strategy will allow a cost-effective diagnosis confirmation as well as early administration of treatment with oral cysteamine. A higher resolution version of the Graphical abstract is available as Supplementary information.

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.

Deficiency of the sedoheptulose kinase (Shpk) does not alter the ability of hematopoietic stem cells to rescue cystinosis in the mouse model

Cystinosis is an autosomal recessive lysosomal storage disorder caused by mutations in the CTNS gene encoding the lysosomal cystine transporter, cystinosin, and leading to multi-organ degeneration including kidney failure. A clinical trial for cystinosis is ongoing to test the safety and efficacy of transplantation of autologous hematopoietic stem and progenitor cells (HSPCs) ex vivo gene-modified to introduce functional CTNS cDNA. Preclinical studies in Ctns−/− mice previously showed that a single HSPC transplantation led to significant tissue cystine decrease and long-term tissue preservation. The main mechanism of action involves the differentiation of the transplanted HSPCs into macrophages within tissues and transfer of cystinosin-bearing lysosomes to the diseased cells via tunneling nanotubes. However, a major concern was that the most common cystinosis-causing mutation in humans is a 57-kb deletion that eliminates not only CTNS but also the adjacent sedopheptulose kinase SHPK/CARKL gene encoding a metabolic enzyme that influences macrophage polarization. Here, we investigated if absence of Shpk could negatively impact the efficiency of transplanted HSPCs to differentiate into macrophages within tissues and then to prevent cystinosis rescue. We generated Shpk knockout mouse models and detected a phenotype consisting of perturbations in the pentose phosphate pathway (PPP), the metabolic shunt regulated by SHPK. Shpk−/− mice also recapitulated the urinary excretion of sedoheptulose and erythritol found in cystinosis patients homozygous for the 57-kb deletion. Transplantation of Shpk−/−-HSPCs into Ctns−/− mice resulted in significant reduction in tissue cystine load and restoration of Ctns expression, as well as improved kidney architecture comparable to WT-HSPC recipients. Altogether, these data demonstrate that absence of SHPK does not alter the ability of HSPCs to rescue cystinosis, and then patients homozygous for the 57-kb deletion should benefit from ex vivo gene therapy and can be enrolled in the ongoing clinical trial. However, because of the limits inherent to animal models, outcomes of this patient population will be carefully compared to the other enrolled subjects.

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.

A 57 kB Genomic Deletion Causing CTNS Loss of Function Contributes to the CTNS Mutational Spectrum in the Middle East.

Background: Nephropathic Cystinosis, the most common cause of renal Fanconi syndrome, is a lysosomal transport disorder with an autosomal recessive inheritance pattern. A large number of mutations in CTNS have been identified as causative to date. A 57 kb deletion encompassing parts of CTNS is most commonly identified in Caucasians but this allele has not been identified in individuals of Eastern Mediterranean, Middle Eastern, Persian, or Arab origin to date.Methods and Results: Implementing whole exome sequencing (WES) in a consanguineous Iranian family, we identified this large deletion affecting CTNS in a patient initially presenting with hypokalemic metabolic alkalosis symptoms and considerable proteinuria.Conclusion: We show WES is a cost and time efficient genetic diagnostics modality to identify the underlying molecular pathology in Cystinosis individuals and provide a summary of all previously reported CTNS alleles in the Middle east population. Our work also highlights the importance to consider the 57-kb deletion as underlying genetic cause in non-European populations, including the Middle East. Limited diagnostic modalities for Cystinosis in developing countries could account for the lack of previously reported cases in these populations carrying this allele. Further, our findings emphasize the utility of WES to define genetic causes in clinically poorly defined phenotypes and demonstrate the requirement of Copy number variation (CNV) analysis of WES data.

Impact of atypical mitochondrial cyclic-AMP level in nephropathic cystinosis.

Nephropathic cystinosis (NC) is a rare disease caused by mutations in the CTNS gene encoding for cystinosin, a lysosomal transmembrane cystine/H+ symporter, which promotes the efflux of cystine from lysosomes to cytosol. NC is the most frequent cause of Fanconi syndrome (FS) in young children, the molecular basis of which is not well established. Proximal tubular cells have very high metabolic rate due to the active transport of many solutes. Not surprisingly, mitochondrial disorders are often characterized by FS. A similar mechanism may also apply to NC. Because cAMP has regulatory properties on mitochondrial function, we have analyzed cAMP levels and mitochondrial targets in CTNS-/- conditionally immortalized proximal tubular epithelial cells (ciPTEC) carrying the classical homozygous 57-kb deletion (delCTNS-/-) or with compound heterozygous loss-of-function mutations (mutCTNS-/-). Compared to wild-type cells, cystinotic cells had significantly lower mitochondrial cAMP levels (delCTNS-/- ciPTEC by 56% ± 10.5, P < 0.0001; mutCTNS-/- by 26% ± 4.3, P < 0.001), complex I and V activities, mitochondrial membrane potential, and SIRT3 protein levels, which were associated with increased mitochondrial fragmentation. Reduction of complex I and V activities was associated with lower expression of part of their subunits. Treatment with the non-hydrolysable cAMP analog 8-Br-cAMP restored mitochondrial potential and corrected mitochondria morphology. Treatment with cysteamine, which reduces the intra-lysosomal cystine, was able to restore mitochondrial cAMP levels, as well as most other abnormal mitochondrial findings. These observations were validated in CTNS-silenced HK-2 cells, indicating a pivotal role of mitochondrial cAMP in the proximal tubular dysfunction observed in NC.

&amp;lt;i&amp;gt;CTNS&amp;lt;/i&amp;gt; Molecular Genetics Profile in a Portuguese Cystinosis Population

Background: Cystinosis is a multisystemic autosomal recessive deficiency of the lysosomal membrane transporter protein (cystinosin) caused by mutations in CTNS gene. Objective: This study summarizes the Portuguese experience in the diagnosis and management of patients with this rare disease over the past few years and reports recurrent mutations in the CTNS gene. Methods: Unrelated patients from different pediatric and adult hospitals all over Portugal with non-nephrotic proteinuria, hypercalciuria, hypokalemia impaired proximal reabsorption of amino acids, glycosuria and hypophosphatemia, suggestive of a Fanconi syndrome and ocular problems, were studied. Intra-leukocyte cystine levels were determined and molecular analysis was performed, to determine the presence or absence of the 57-kb deletion in CTNS, followed by direct sequencing of the coding exons of CTNS. Results: From 1998 to 2017, twenty-one cystinotic patients were biochemically diagnosed. From the remaining seventeen (four deceased), eleven were studied for CTNS gene. Five out of eleven patients were homozygous for the 57-kb deletion (10/22; 45.5%), and other five were compound heterozygous for this variant (15/22; 68.2%). The other mutations found were p.Q128X (c.721 C>T; 2/22), p.S139F (c.755 C>T; 4/22) and c.18-21delGACT (p.T7FfsX7; 1/22). All of these seventeen cystinotic patients are in treatment. Approximately 84% are adults, 16% are young children, and 54.5% are kidney transplant recipient. Conclusions: The authors would like to emphasize the importance of first screening for the 57-kb deletion since it is very common in our population. This genetic study is the first in our country and it could be the basis for future genetic counseling in Portuguese population.

The Clinical and Mutational Spectrum of Turkish Patients with Cystinosis.

Infantile nephropathic cystinosis is a severe disease that occurs due to mutations in the cystinosis gene, and it is characterized by progressive dysfunction of multiple organs; >100 cystinosis gene mutations have been identified in multiple populations. Our study aimed to identify the clinical characteristics and spectrum of cystinosis gene mutations in Turkish pediatric patients with cystinosis. We identified the clinical characteristics and spectrum of cystinosis gene mutations in Turkish patients with cystinosis in a multicenter registry that was established for data collection. The data were extracted from this registry and analyzed. In total, 136 patients (75 men and 61 women) were enrolled in the study. The most common clinical findings were growth retardation, polyuria, and loss of appetite. None of the patients had the 57-kb deletion, but seven novel mutations were identified. The most common mutations identified were c.681G>A (p.Glu227Glu; 31%), c.1015G>A (p.Gly339Arg; 22%), and c.18_21 del (p.Thr7Phefs*7; 14%). These mutations were associated with earlier age of disease onset than the other mutations. To understand the effects of these allelic variants on clinical progression, the mutations were categorized into two major groups (missense versus deletion/duplication/splice site). Although patients with missense mutations had a better eGFR at the last follow-up visit, the difference was not significant. Patients in whom treatment began at age <2 years old had later onset of ESRD (P=0.02). Time to ESRD did not differ between the patients with group 1 and group 2 mutations. The most common cystinosis gene mutations identified in Turkey were c.681G>A (p.Glu227Glu), c.1015G>A (p.Gly339Arg), and c.18_21 del (p.Thr7Phefs*7). Patients with less severe cystinosis gene mutations tend to have better kidney outcome.

CTNS molecular genetics profile in a Persian nephropathic cystinosis population

PurposeIn this report, we document the CTNS gene mutations of 28 Iranian patients with nephropathic cystinosis age 1–17 years. All presented initially with severe failure to thrive, polyuria, and polydipsia. MethodsCystinosis was primarily diagnosed by a pediatric nephrologist and then referred to the Iran University of Medical Sciences genetics clinic for consultation and molecular analysis, which involved polymerase chain reaction (PCR) amplification to determine the presence or absence of the 57-kb founder deletion in CTNS, followed by direct sequencing of the coding exons of CTNS. ResultsThe common 57-kb deletion was not observed in any of the 28 Iranian patients. In 14 of 28 patients (50%), mutations were observed in exons 6 and 7. No mutation was detected in exon 5, and only one (3.6%) patient with cystinosis showed a previously reported 4-bp deletion in exon 3 of CTNS. Four patients (14.3%) had a previously reported mutation (c.969C>A; p.N323K) in exon 11, and five (18%) had novel homozygous deletions in exon 6 leading to premature truncation of the protein. These deletions included c.323delA; p.Q108RfsX10 in three individuals and c.257-258delCT; p.S86FfsX37 in two cases. Other frame-shift mutations were all novel homozygous single base pair deletion/insertions including one in CTNS exon 9 (c.661insT; p.V221CfsX6), and four (14.3%) in exon 4, i.e., c.92insG; p.V31GfsX28 in two and c.120delC; p.T40TfsX10 in two. In total, we identified eight previously reported mutations and eight novel mutations in our patients. The only detected splice site mutation (IVS3-2A>C) was associated with the insertion mutation in the exon 9. ConclusionThis study, the first molecular genetic analysis of non-ethnic-specific Iranian nephropathic cystinosis patients, may provide guidance for molecular diagnostics of cystinosis in Iran.

CTNS molecular genetics profile in a Persian nephropathic cystinosis population

PurposeIn this report, we document the CTNS gene mutations of 28 Iranian patients with nephropathic cystinosis age 1–17 years. All presented initially with severe failure to thrive, polyuria, and polydipsia. MethodsCystinosis was primarily diagnosed by a pediatric nephrologist and then referred to the Iran University of Medical Sciences genetics clinic for consultation and molecular analysis, which involved polymerase chain reaction (PCR) amplification to determine the presence or absence of the 57-kb founder deletion in CTNS, followed by direct sequencing of the coding exons of CTNS. ResultsThe common 57-kb deletion was not observed in any of the 28 Iranian patients. In 14 of 28 patients (50%), mutations were observed in exons 6 and 7. No mutation was detected in exon 5, and only one (3.6%) patient with cystinosis showed a previously reported 4-bp deletion in exon 3 of CTNS. Four patients (14.3%) had a previously reported mutation (c.969C>A; p.N323K) in exon 11, and five (18%) had novel homozygous deletions in exon 6 leading to premature truncation of the protein. These deletions included c.323delA; p.Q108RfsX10 in three individuals and c.257-258delCT; p.S86FfsX37 in two cases. Other frame-shift mutations were all novel homozygous single base pair deletion/insertions including one in CTNS exon 9 (c.661insT; p.V221CfsX6), and four (14.3%) in exon 4, i.e., c.92insG; p.V31GfsX28 in two and c.120delC; p.T40TfsX10 in two. In total, we identified eight previously reported mutations and eight novel mutations in our patients. The only detected splice site mutation (IVS3-2A>C) was associated with the insertion mutation in the exon 9. ConclusionThis study, the first molecular genetic analysis of non-ethnic-specific Iranian nephropathic cystinosis patients, may provide guidance for molecular diagnostics of cystinosis in Iran.

TRPV1 dysfunction in cystinosis patients harboring the homozygous 57 kb deletion.

Cystinosis is a rare autosomal recessive disorder characterized by lysosomal cystine accumulation due to loss of function of the lysosomal cystine transporter (CTNS). The most common mutation in cystinosis patients of Northern Europe consists of a 57-kb deletion. This deletion not only inactivates the CTNS gene but also extends into the non-coding region upstream of the start codon of the TRPV1 gene, encoding the capsaicin- and heat-sensitive ion channel TRPV1. To evaluate the consequences of the 57-kb deletion on functional TRPV1 expression, we compared thermal, mechanical and chemical sensitivity of cystinosis patients with matched healthy controls. Whereas patients heterozygous for the 57-kb deletion showed normal sensory responses, homozygous subjects exhibited a 60% reduction in vasodilation and pain evoked by capsaicin, as well as an increase in heat detection threshold. Responses to cold, mechanical stimuli or cinnamaldehyde, an agonist of the related nociceptor channel TRPA1, were unaltered. We conclude that cystinosis patients homozygous for the 57-kb deletion exhibit a strong reduction of TRPV1 function, leading to sensory deficiencies akin to the phenotype of TRPV1-deficient mice. These deficits may account for the reported sensory alterations and thermoregulatory deficits in these patients, and provide a paradigm for life-long TRPV1 deficiency in humans.

Molecular analysis of the CTNS gene in Jordanian families with nephropathic cystinosis

ObjectiveNephropathic cystinosis is an autosomal recessive lysosomal storage disorder that is characterised by the accumulation of the amino acid cystine in several body tissues due to a mutation in the CTNS gene, which encodes the cystinosin protein. The aim of this study was to sequence the coding exons of the CTNS gene in five different Jordanian families and one family from Sudan with nephropathic cystinosis. MethodsProbands initially presented with Fanconi syndrome symptoms. An eye examination showed the accumulation of cystine crystals in the cornea by the age of 2 years, suggesting cystinosis. All of the coding exons and flanking intronic sequences and the promoter region of the CTNS gene were amplified using polymerase chain reaction and subjected to sequencing. ResultsNone of the probands in this study carried the European 57-kb deletion in the CTNS gene. Seven variants in the coding and promoter sequence of the CTNS gene were identified in the probands of this study. Two of these variants were a CTNS mutation that was previously identified in a heterozygous genotype in two different patients of European descendant. The two mutations were c.829dupA in exon 10 and c.890G>A in exon 11. The proband of family 2 was compound-heterozygous for the two mutations. ConclusionThis study is the first molecular study of infantile nephropathic cystinosis in Jordan. We successfully identified the causative CTNS mutations in Jordanian families. The results provide a basis for the early detection of the disease using molecular tools in a highly consanguineous Jordanian population.

Molecular analysis of the CTNS gene in Jordanian families with nephropathic cystinosis

ObjectiveNephropathic cystinosis is an autosomal recessive lysosomal storage disorder that is characterised by the accumulation of the amino acid cystine in several body tissues due to a mutation in the CTNS gene, which encodes the cystinosin protein. The aim of this study was to sequence the coding exons of the CTNS gene in five different Jordanian families and one family from Sudan with nephropathic cystinosis. MethodsProbands initially presented with Fanconi syndrome symptoms. An eye examination showed the accumulation of cystine crystals in the cornea by the age of 2 years, suggesting cystinosis. All of the coding exons and flanking intronic sequences and the promoter region of the CTNS gene were amplified using polymerase chain reaction and subjected to sequencing. ResultsNone of the probands in this study carried the European 57-kb deletion in the CTNS gene. Seven variants in the coding and promoter sequence of the CTNS gene were identified in the probands of this study. Two of these variants were a CTNS mutation that was previously identified in a heterozygous genotype in two different patients of European descendant. The two mutations were c.829dupA in exon 10 and c.890G>A in exon 11. The proband of family 2 was compound-heterozygous for the two mutations. ConclusionThis study is the first molecular study of infantile nephropathic cystinosis in Jordan. We successfully identified the causative CTNS mutations in Jordanian families. The results provide a basis for the early detection of the disease using molecular tools in a highly consanguineous Jordanian population.

Genetic basis of cystinosis in Tunisian patients: Identification of novel mutation in CTNS gene

Nephropathic cystinosis (NC) is an autosomal recessive disorder characterized by defective transport of cystine across the lysosomal membrane and resulting in renal, ophthalmic, and other organ abnormalities. Mutations in the CTNS gene cause a deficiency of the transport protein, cystinosin. This study was performed to investigate mutations of the CTNS gene in three Tunisian families with NC.Polymerase chain reaction (PCR), ARMS multiplex PCR and direct sequencing were performed for molecular characterization of the CTNS gene in 3 unrelated Tunisian patients and their parents. Based on family history, prenatal diagnosis (PND) was performed in fetal DNA isolated from chorionic villi obtained at 10–12 weeks of gestation.None of the patients showed the most common 57-kb deletion in heterozygous or homozygous status. One patient was homozygous for the previously reported mutation c.1515G>A (p.G308R). One patient presented the novel gross deletion of 20,327bp. One was homozygote for the previously reported mutation c.771_793del (p.Gly258Serfs*30). In addition, eight polymorphisms were identified in the 3 patients and their parents. The prenatal diagnosis in one family showed that the fetus DNA was heterozygous for the c.771_793del (p.Gly258Serfs*30) mutation.This study expands the mutational and population spectrum of NC, representing the first molecular diagnosis of NC in Tunisian population. The mutation screening of the CTNS gene was used for prenatal diagnosis to prevent and/or limit this inheritable disease in our country where the families are particularly large and have a high rate of consanguinity.

Genetic basis of cystinosis in Turkish patients: a single-center experience.

We report the molecular findings for the CTNS gene in 12 Turkish cystinosis patients aged 7-29 years. All presented initially with severe failure to thrive, polyuria, and polydipsia. Cystinosis was diagnosed at age 1 month to 9 years. Seven patients reached end-stage renal failure at ages ranging from 6.5 to 15 years. Whereas three of the remaining five have renal Fanconi syndrome with proteinuria, two have had kidney failure of varying degrees. Molecular analyses involved an initial multiplex polymerase chain reaction (PCR) to determine the presence or absence of the 57-kb northern European founder deletion in CTNS, followed by sequencing of the ten coding exons of CTNS. Comprehensive mutation analysis verified that none of the 12 patients carried the common 57-kb deletion. We identified four previously reported nucleotide variations associated with cystinosis and five new variants: a 10-kb deletion, three missense variants, and a nucleotide substitution in a potential branch point site of intron 4. This study is the first molecular analysis of Turkish cystinosis patients and provides guidance for the molecular diagnosis of cystinosis in this population.

Elevated concentrations of sedoheptulose in bloodspots of patients with cystinosis caused by the 57-kb deletion: Implications for diagnostics and neonatal screening

Cystinosis is an autosomal recessive lysosomal storage disease caused by mutations in CTNS. The most prevalent CTNS mutation is a homozygous 57-kb deletion that also includes an adjacent gene named SHPK ( CARKL), encoding sedoheptulokinase. Patients with this deletion have elevated urinary concentrations of sedoheptulose. Using derivatisation with pentafluorobenzyl hydroxylamine and liquid chromatography–tandem mass spectrometry (LC–MS/MS), we developed a new sensitive method for the quantification of sedoheptulose in dried blood spots. This method can be utilized as a quick screening test to detect cystinosis patients homozygous for the 57-kb deletion in CTNS; which is the most common mutation of cystinosis. Sedoheptulose concentrations in the deleted patients were 6 to 23 times above the upper limit for controls. The assessment of sedoheptulose in a bloodspot from a known cystinosis patient homozygous for the 57-kb deletion retrieved from the Dutch neonatal screening program showed that sedoheptulose was already elevated in the neonatal period. There was no overlap in sedoheptulose levels between cystinosis patients homozygous for the 57-kb deletion and cystinosis patients not homozygous for this deletion. Our presented method can be used prior to mutation analysis to detect cystinosis patients homozygous for the 57-kb deletion. We feel that the presented method enables fast (pre)-symptomatic detection of cystinosis patients homozygous for the 57-kb deletion, allowing early treatment.

Analysis of the CTNS Gene in Nephropathic Cystinosis Mexican Patients: Report of Four Novel Mutations and Identification of a False Positive 57-kb Deletion Genotype with LDM-2/Exon 4 Multiplex PCR Assay

Identify CTNS gene mutations in nephropathic cystinosis Mexican patients. Eleven patients were included, nine presenting infantile nephropathic cystinosis and two siblings with the juvenile phenotype. The common 57-kb deletion was detected by multiplex PCR using large deletion marker-2 (LDM-2)/exon 4 set primers. Those alleles negative for 57-kb deletion were screened by single strand confirmation polymorphism (SSCP) and subsequent direct sequencing. In our sample, five mutations previously reported are identified: 57-kb deletion, EX4_EX5del, c.985_986insA, c.357_360delGACT, and c.537_557del. We detect a false assignation of 57-kb deletion homozygous genotype by using the LDM-2/exon 4 primers. In addition, four novel and severe mutations are identified: c.379delC, c.1090_1093delACCAinsCG, c.986C>G (p.T216R), and c.400+5G>A. Our sample of Mexican patients display allelic heterogeneity as compared to European or North American cystinosis cases. The identification of novel mutations might suggest the presence of exclusive American CTNS alleles in Mexican population. In order to prevent the false positive assignation of 57-kb deletion genotype, as caused by the presence of another type of intragenic CTNS gross deletion, we propose to analyze a different control CTNS exon to those originally reported in both LDM multiplex PCR assays, especially when parental DNA samples are not available.