Complications of nephropathic cystinosis after renal failure

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, and 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.

Event-related potential (ERP) evidence for visual processing differences in children and adults with cystinosis (CTNS gene mutations)

BACKGROUND

Cystinosis, a rare lysosomal storage disease caused by mutations in the CTNS gene, is characterized by cystine crystallization and accumulation within multiple tissues, including kidney and brain. Its impact on neural function appears mild relative to its effects on other organs during early disease, but since therapeutic advances have led to substantially increased life expectancy, neurological implications are of increasing interest, necessitating deeper understanding of the impact of cystinosis on neurocognitive function. Behavioral difficulties have been reported in cystinosis in the visual domain. Very little is known, however, about how the brains of people living with cystinosis process visual information. This is especially interesting given that cystine accumulation in the cornea and posterior ocular structures is a hallmark of cystinosis.

METHODS

Here, high-density scalp electrophysiology was recorded to visual stimuli (during a Go/No-Go task) to investigate visual processing in individuals with cystinosis, compared to age-matched controls. Analyses focused on early stages of cortical visual processing.

RESULTS

The groups differed in their initial cortical response, with individuals with cystinosis exhibiting a significantly larger visual evoked potential (VEP) in the 130-150 ms time window. The groups also differed in the associations between neural responses and verbal abilities: While controls with higher IQ scores presented larger neural responses, that relationship was not observed in cystinosis.

CONCLUSIONS

The enlarged VEP in cystinosis could be the result of cortical hyperexcitability and/or differences in attentional engagement and explain, at least partially, the visual and visual-spatial difficulties described in this population.

Event-related potential (ERP) evidence for early visual processing differences in children and adults with Cystinosis (CTNS gene mutations)

Background

Cystinosis, a rare lysosomal storage disease caused by mutations in the CTNS gene, is characterized by cystine crystallization and accumulation within multiple tissues, including kidney and brain. Its impact on neural function appears mild relative to its effects on other organs during early disease, but since therapeutic advances have led to substantially increased life expectancy, neurological implications are of increasing interest, necessitating deeper understanding of the impact of cystinosis on neurocognitive function. Behavioral difficulties have been reported in cystinosis in the visual domain. Very little is known, however, about how the brains of people living with cystinosis process visual information. This is especially interesting given that cystine accumulation in the cornea and posterior ocular structures is a hallmark of cystinosis.

Methods

Here, high-density scalp electrophysiology was recorded to visual stimuli (during a Go/No-Go task) to investigate early visual processing in individuals with cystinosis, compared to age-matched controls. Analyses focused on early stages of cortical visual processing.

Results

The groups differed in their initial cortical response, with individuals with cystinosis exhibiting a significantly larger visual evoked potential (VEP) in the 130-150 ms time window. The groups also differed in the associations between neural responses and verbal abilities: While controls with higher IQ scores presented larger neural responses, that relationship was not observed in cystinosis.

Conclusions

The enlarged VEP in cystinosis could be the result of cortical hyperexcitability and/or differences in attentional engagement and explain, at least partially, the visual and visual-spatial difficulties described in this population.

Event-related potential (ERP) evidence of early visual processing differences in cystinosis

Cystinosis, a rare lysosomal storage disease, is characterized by cystine crystallization and accumulation within tissues and organs, including the kidneys and brain. Its impact on neural function appears mild relative to its effects on other organs, but therapeutic advances have led to substantially increased life expectancy, necessitating deeper understanding of its impact on neurocognitive function. Behavioral difficulties have been reported in cystinosis in the visual and visual-processing domain. Very little is known, however, about how the brains of people living with cystinosis process visual information, although cysteamine accumulation in the retina is a prominent feature of cystinosis. Here, electrophysiology was recorded during a Go/No-Go task to investigate early visual processing in cystinosis, compared to an age-matched control group. Analyses focused on early stages of cortical visual processing. The groups differed in their initial cortical response, with individuals with cystinosis exhibiting a significantly larger visual evoked potential (VEP) in the 130 to 150 ms time window. The timing and topography of this response suggested an enhanced P1 in cystinosis that could be the result of cortical hyperexcitability and/or differences in attentional engagement and explain, at least partially, the visual and visual-spatial difficulties described in this population. The groups also differed in the associations between neural responses and verbal abilities: While controls with higher IQ scores presented larger neural responses, that relationship was not observed in cystinosis.

Posterior Segment Involvement in Infantile Nephropathic Cystinosis - A Review

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

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.

Central Nervous System Complications in Cystinosis: The Role of Neuroimaging

Despite improvement in the specific treatment, clinical and anatomo-functional central nervous system (CNS) abnormalities of various severities are still observed in cystinosis patients. Patients who develop CNS complications today have a worse compliance to cysteamine treatment. Radiological studies have shown that cortical or central (ventriculomegaly) atrophy is observed in more than two thirds of cystinosis patients’ magnetic resonance imaging (MRI) and correlates with the intelligence quotient score. Half of cystinosis patients have marked aspecific white matter hyperintensities. The development of advanced neuroimaging techniques provides new tools to further investigate CNS complications. A recent neuroimaging study using a voxel-based morphometry approach showed that cystinosis patients present a decreased grey matter volume in the left middle frontal gyrus. Diffusion tensor imaging studies have shown white matter microstructure abnormalities in children and adults with cystinosis, respectively in areas of the dorsal visual pathway and within the corpus callosum’s body. Finally, leucocyte cystine levels are associated with decreased resting cerebral blood flow, measured by arterial spin labelling, in the frontal cortex, which could be associated with the neurocognitive deficits described in these patients. These results reinforce the relevance of neuroimaging studies to further understand the mechanisms that underline CNS impairments.

Gold nanoparticle synthesis in contact lenses for drug-less ocular cystinosis treatment

PURPOSE

To develop gold nanoparticles-loaded contact lens ("GoldinLens") to bind a significant mass of cystine on the surface of the gold nanoparticles (GNPs) for cystinosis treatment due to the reaction between cystine and gold.

METHODS

The GoldinLens was manufactured by synthesizing GNPs inside the preformed contact lens matrix by first loading the lenses (Moist and TrueEye) with gold precursor followed by reduction (with sodium borohydride or trisodium citrate) to gold atoms, which nucleated to GNPs inside the polymeric matrix. The lenses were characterized by SEM, XRD, UV-Vis spectroscopy and mass of GNPs loaded in the lens was determined by direct measurement of mass. Manufactured lenses were soaked in cystine solution for cystine uptake in vitro.

RESULTS

Results show that gold loading in the contact lens increases linearly with gold precursor concentration and number of repetitions of the manufacturing process. The stronger reducing agent sodium borohydride resulted in higher gold loading, with the loading being higher in the Moist lenses due to higher diffusivity of the reducing agent into the lens. However, GNPs were smaller in size and relatively monodispersed in TruEye GoldinLens, resulting in higher cystine uptake of 47 μg/lens over 24 h (vs. 33 μg/lens for Moist GoldinLens). However, the rate of this uptake was higher for Moist GoldiLens (8.25 vs. 2.35 μg/h), with the maximum uptake occurring in one hour (vs. five hours).

CONCLUSION

A method for manufacturing GoldinLens, wherein small gold nanoparticles are trapped in contact lenses, has been developed for drugless cystinosis treatment. The lenses withdraw cystine molecules from the surrounding milieu, with the TrueEye GoldinLens being superior for the extent of, while Moist GoldinLens is superior for rate of cystine removal. GoldinLenses of this study can be used for drugless cystine removal cystinosis treatment with one- or five-hour wear at a time.

Assessing the integrity of auditory processing and sensory memory in adults with cystinosis (CTNS gene mutations)

Background

Cystinosis, a rare lysosomal storage disease, is characterized by cystine crystallization and accumulation within tissues and organs, including the kidneys and brain. Its impact on neural function appears mild relative to its effects on other organs, but therapeutic advances have led to substantially increased life expectancy, necessitating deeper understanding of its impact on neurocognitive function in adulthood. We previously demonstrated intact auditory sensory processing, accompanied by mild sensory memory difficulties, in children and adolescents with cystinosis.

Methods

We investigated whether further progressive decrements in these processes would be observed in adults with cystinosis, comparing high-density auditory-evoked potential (AEP) recordings from adults with cystinosis (N = 15; ages: 19–38 years) to those of age-matched controls (N = 17). We employed a duration oddball paradigm with different stimulation rates, in which participants passively listened to regularly occurring standard tones interspersed with infrequently occurring deviant tones. Analyses focused on AEP components reflecting auditory sensory-perceptual processing (N1 and P2), sensory memory (mismatch negativity, MMN), and attentional orienting (P3a).

Results

Overall, adults with cystinosis produced highly similar sensory-perceptual AEP responses to those observed in controls suggesting intact early auditory cortical processing. However, significantly increased P2 and P3a amplitudes and reduced MMN at slower stimulation rates were observed, suggesting mild-to-moderate changes in auditory sensory memory and attentional processing. While cognitive testing revealed lower scores on verbal IQ and perceptual reasoning in cystinosis, these did not correlate with the AEP measures.

Conclusions

These neurophysiological data point to the emergence of subtle auditory processing deficits in early adulthood in cystinosis, warranting further investigation of memory and attentional processes in this population, and of their consequences for perceptual and cognitive function.

Central nervous system complications in adult cystinosis patients

Little is known about the long-term progression of adult nephropathic cystinosis patients. Our objective was to study central nervous system complications in cystinosis patients in the era of early cysteamine treatment, using advanced neuroimaging techniques. Neurological examination and multimodal brain 3 Tesla MRI were performed in 21 adult cystinosis patients, including 18 infantile cystinosis patients, 20 controls matched for age and renal function, and 12 healthy controls. Differences in gray matter volume and rest cerebral blood flow (CBF) using arterial spin labeling sequence were investigated using whole-brain voxel-based approach. Median age was 33.8 years (18.7-65.8). Seven patients (38.9%) presented with at least one central nervous system clinical abnormality: two (11.1%) with seizures, three (16.7%) with memory defects, five (27.8%) with cognitive defect, and one (5.5%) with stroke-like episode. These patients had a worse compliance to treatment (compliance score 2 vs 1, P = .03) and received a lower median cysteamine dose (0.9 g/day vs 2.1 g/day, P = .02). Among patients with infantile cystinosis, 13 (72.2%) showed cortical atrophy, which was absent in controls, but it was not correlated with symptoms. Cystinosis patients showed a significant gray matter decrease in the middle frontal gyrus compared with healthy controls and a significant negative correlation between the cystine blood level and rest CBF was observed in the right superior frontal gyrus, a region associated with executive function. Compliance to cysteamine treatment is a major concern in these adult patients and could have an impact on the development of neurological and cognitive complications.

Impaired auditory sensory memory in Cystinosis despite typical sensory processing: A high-density electrical mapping study of the mismatch negativity (MMN)

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Children and adolescents with Cystinosis show similar N1 responses to their age-matched peers.

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Children and adolescents with Cystinosis show reduced MMNs for longer SOAs.

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Our results suggest typical auditory processing, but impaired sensory memory in Cystinosis.

Cystinosis, a genetic rare disease characterized by cystine accumulation and crystallization, results in significant damage in a multitude of tissues and organs, such as the kidney, thyroid, eye, and brain. While Cystinosis’ impact on brain function is relatively mild compared to its effects on other organs, the increased lifespan of this population and thus potential for productive societal contributions have led to increased interest on the effects on brain function. Nevertheless, and despite some evidence of structural brain differences, the neural impact of the mutation is still not well characterized. Here, using a passive duration oddball paradigm (with different stimulus onset asynchronies (SOAs), representing different levels of demand on memory) and high-density electrophysiology, we tested basic auditory processing in a group of 22 children and adolescents diagnosed with Cystinosis (age range: 6-17 years old) and in neurotypical age-matched controls (N = 24). We examined whether the N1 and mismatch negativity (MMN) significantly differed between the groups and if those neural measures correlated with verbal and non-verbal IQ. Individuals diagnosed with Cystinosis presented similar N1 responses to their age-matched peers, indicating typical basic auditory processing in this population. However, whereas both groups showed similar MMN responses for the shortest (450 ms) SOA, suggesting intact change detection and sensory memory, individuals diagnosed with Cystinosis presented clearly reduced responses for the longer (900 ms and 1800 ms) SOAs. This could indicate reduced duration auditory sensory memory traces, and thus sensory memory impairment, in children and adolescents diagnosed with Cystinosis. Future work addressing other aspects of sensory and working memory is needed to understand the underlying bases of the differences described here, and their implication for higher order processing.

Cystinosis distal myopathy, novel clinical, pathological and genetic features

Nephropathic cystinosis is an autosomal recessive lysosomal disease in which cystine cannot exit the lysosome to complete its degradation in the cytoplasm, thus accumulating in tissues. Some patients develop a distal myopathy involving mainly hand muscles. Myopathology descriptions from only 5 patients are available in the literature. We present a comprehensive clinical, pathological and genetic description of 3 patients from 2 families with nephropathic cystinosis. Intrafamiliar variability was detected in one family in which one sibling developed a severe distal myopathy while the other sibling did not show any signs of skeletal muscle involvement. One of the patients was on treatment with Cysteamine for over 12 years but still developed the usual complications of nephropathic cystinosis in his twenties. Novel pathological findings consisting in sarcoplasmic deposits reactive for slow myosin were identified. Three previously known and one novel mutation are reported. Nephropathic cystinosis should be included in the differential diagnosis of distal myopathies in those with early renal failure. Novel clinical and pathological features are reported here contributing to the characterization of the muscle involvement in nephropathic cystinosis.

Cysteamine therapy delays the progression of nephropathic cystinosis in late adolescents and adults

Nephropathic cystinosis is a multisystem autosomal recessive disease caused by cystine accumulation, which is usually treated by oral cysteamine. In order to determine long-term effects of this therapy, we enrolled 86 adult patients (mean age 26.7 years) diagnosed with nephropathic cystinosis, 75 of whom received cysteamine. Therapy was initiated at a mean age of 9.9 years with a mean duration of 17.4 years. By last follow-up, 78 patients had end-stage renal disease (mean age 11.1 years), 62 had hypothyroidism (mean age 13.4), 48 developed diabetes (mean age 17.1 years), and 32 had neuromuscular disorders (mean age 23.3 years). Initiating cysteamine therapy before 5 years of age significantly decreased the incidence and delayed the onset of end-stage renal disease, and significantly delayed the onset of hypothyroidism, diabetes, and neuromuscular disorders. The development of diabetes and hypothyroidism was still significantly delayed, however, in patients in whom therapy was initiated after 5 years of age, compared with untreated patients. The life expectancy was significantly improved in cysteamine-treated versus untreated patients. Thus, cysteamine decreases and delays the onset of complications and improves life expectancy in cystinosis. Hence, cysteamine therapy should be introduced as early as possible during childhood and maintained lifelong.

Natural history of adolescent-onset cystinosis

Cystinosis is a rare autosomal recessive disease caused by mutations of the CTNS gene in which cystine accumulates throughout the body as a result of a defective efflux of cystine from lysosomes. Three phenotypic forms have been described according to the age of onset and the severity of the clinical symptoms: infantile, intermediate, and ocular non-nephropathic cystinosis. Here we report the natural history of cystinosis in a 55-year-old man with intermediate nephropathic cystinosis diagnosed at 9 years of age. Although tubulopathy was unnoticed in the early years, he required transplantation at age 16. Sequencing analysis of all the CTNS exons revealed that the proband is homozygous for a 21-bp in-frame deletion in exon 5 (c. 198_218del21), resulting in an in-frame deletion of 7 amino acids from the N-terminal domain of the cystinosin protein. Our patient has had relatively mild extra-renal disease despite lack of early cysteamine therapy. He has been able to attend university and pursue a professional career into the 6th decade.

Visual and verbal learning in a genetic metabolic disorder

Visual and verbal learning in a genetic metabolic disorder (cystinosis) were examined in the following three studies. The goal of Study I was to provide a normative database and establish the reliability and validity of a new test of visual learning and memory (Visual Learning and Memory Test; VLMT) that was modeled after a widely used test of verbal learning and memory (California Verbal Learning Test; CVLT). One hundred seventy-two neurologically intact individuals ages 5 years through 50 years were administered the VLMT and the CVLT. Normative data were collected and the results suggested that the VLMT is a reliable and valid new measure of visual learning and memory. The aim of Study II was to examine possible dissociations between verbal and visual learning and memory performances in individuals with cystinosis as well as to assess changes in performance as individuals with the disorder age. Thirty-seven individuals with cystinosis and 37 matched controls were administered a new test of visual learning and memory (Visual Learning and Memory Test; VLMT) and the California Verbal Learning Test (CVLT). Individuals with cystinosis performed at a lower level than controls on almost all indices of visual learning and memory while no differences were found between the groups on the verbal measure. Examination of the results on the VLMT indicated that the visual learning and memory impairment in cystinosis may result from difficulty with processing visual information quickly. Study III aimed to remediate the observed visual learning and memory deficit by implementing an intervention that increased the exposure time for visual stimuli. Fifteen individuals with cystinosis were administered a version of the VLMT in which the stimuli were exposed for 3s rather than 1s. Fifteen matched controls were administered the 1-s version of the VLMT. The results of Study III indicated that by increasing the exposure time for each visual stimulus, individuals with cystinosis were able to perform at the same level as control subjects. This is the first study to demonstrate impaired visual learning and spared verbal learning in individuals with cystinosis. These results may provide the foundation for designing cognitive interventions, may lead to further hypotheses regarding the underlying mechanism of the observed visual learning and memory deficit, and have implications for a greater understanding of gene-behavior relationships.

Nephropathic cystinosis: late complications of a multisystemic disease

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

Sedoheptulokinase deficiency due to a 57-kb deletion in cystinosis patients causes urinary accumulation of sedoheptulose: elucidation of the CARKL gene

The most common mutation in the nephropathic cystinosis (CTNS) gene is a homozygous 57-kb deletion that also includes an adjacent gene carbohydrate kinase-like (CARKL). The latter gene encodes a protein that is predicted to function as a carbohydrate kinase. Cystinosis patients with the common 57-kb deletion had strongly elevated urinary concentrations of sedoheptulose (28-451 mmol/mol creatinine; controls and other cystinosis patients <9) and erythritol (234-1110 mmol/mol creatinine; controls and other cystinosis patients <148). Enzyme studies performed on fibroblast homogenates derived from patients carrying the 57-kb deletion revealed 80% reduction in their sedoheptulose phosphorylating activity compared to cystinosis patients with other mutations and controls. This indicates that the CARKL-encoded protein, sedoheptulokinase (SHK), is responsible for the reaction: sedoheptulose + ATP --> sedoheptulose-7-phosphate + ADP and that deletion of CARKL causes urinary accumulation of sedoheptulose and erythritol.

The ocular anomalies in a cystinosis animal model mimic disease pathogenesis

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

Non-verbal deficits in young children with a genetic metabolic disorder: WPPSI-III performance in cystinosis

Cystinosis is a recessive genetic metabolic disorder in which the amino acid cystine accumulates in various organs of the body. Previous studies have demonstrated visuospatial dysfunction in children and adults with this disorder. It is not known whether this is a result of the genetic alteration or an accumulation of cystine in the brain over time. This study investigated patterns of performance in 20 young children with cystinosis (4-7 years) and 20 matched controls on the Wechsler Preschool and Primary Scale of Intelligence-Third Edition (WPPSI-III). The children with cystinosis had a mean Full Scale IQ at the low end of the average range. Their overall cognitive functioning was comprised of average verbal abilities, low average non-verbal abilities, and low average processing speed. Multivariate analyses indicated that the cystinosis and control groups were not significantly different on the verbal subtests. In contrast, the cystinosis group performed significantly more poorly than controls on the performance and processing speed subtests. Although overall intellectual function was in the normal range, young children with cystinosis demonstrated a discrepancy such that non-verbal abilities were poorer relative to verbal abilities. This pattern resembles the cognitive profile found previously in older individuals with cystinosis and indicates that the specific cognitive profile emerges early in development. These findings suggest that the cognitive dysfunction in cystinosis is not merely the result of cystine accumulation over time but may be related to differences in brain development as a consequence of alterations or deletions of the cystinosin gene.

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

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

Cystine Inhibits Creatine Kinase Activity in Pig Retina

BACKGROUND

Cystinosis is an autosomal recessive disorder associated with lysosomal cystine accumulation caused by defective cystine efflux. Visual deficit is a possible consequence of cystine accumulation in cornea and retina. Fibroblasts from cystinotic patients present ATP deficit with intact mitochondrial energy-generating capacity by an unknown mechanism. Considering that creatine kinase is a thiol enzyme crucial for energy homeostasis in retina, and disulfides like cystine may alter thiol enzymes, the main objective of the present study was to investigate the effect of cystine and cysteamine, the drug used for treatment of cystinotic patients, on creatine kinase activity in cytosolic and mitochondrial fractions of the retina from adult pigs.

METHODS

Retina was isolated from 6-month-old Landrace pigs, homogenized and mitochondrial and cytosolic fractions separated by centrifugation. Cytosolic and mitochondrial creatine kinase activities were determined in the presence of different concentrations of cystine and/or cysteamine.

RESULTS

Cystine inhibited the enzyme activity in a dose- and time-dependent manner and cysteamine prevented and reversed the inhibition caused by cystine, suggesting that cystine inhibits creatine kinase activity by oxidation of the sulfhydryl groups of the enzyme.

CONCLUSIONS

Considering that creatine kinase is a crucial enzyme for retina energy homeostasis, in case cystine leaves lysosome these results provide a possible mechanism for cystine toxicity and also another beneficial effect for the use of cysteamine in patients with cystinosis.

Coronary artery and other vascular calcifications in patients with cystinosis after kidney transplantation

Cystinosis, an autosomal recessive disorder of lysosomal cystine accumulation, results from mutations in the CTNS gene that encodes the lysosomal cystine transporter, cystinosin. Renal tubular Fanconi syndrome occurs in infancy, followed by rickets, growth retardation, photophobia, and renal failure, which requires renal transplantation at approximately 10 yr of age. Treatment with cysteamine decreases cellular cystine levels, retards renal deterioration, and allows for normal growth. Patients with a history of inadequate cystine depletion therapy may survive, after renal transplantation, into the third to fifth decades but will experience other, extrarenal complications of the disease. Routine chest and head computed tomography scans of 41 posttransplantation patients with cystinosis were reviewed for vascular calcification. The radiologic procedures had been performed to examine lung and brain parenchyma, so there was little ascertainment bias. Thirteen of the 41 patients had vascular calcification, including 11 with coronary artery calcification. One 25-yr-old man required three-vessel coronary artery bypass graft surgery. There were no significant differences between the 13 patients with calcification and the 28 without calcification in the following parameters: Time on dialysis, frequency of transplantation, hypertension, hypercholesterolemia, homozygosity for the 57-kb deletion in CTNS, serum creatinine, and calcium-phosphate product. However, the finding of vascular calcification correlated directly with duration of life without cysteamine therapy and inversely with duration of life under good cystine-depleting therapy. The accumulation of intracellular cystine itself maybe a risk factor for vascular calcifications, and older patients with cystinosis should be screened for this complication.

Idiopathic intracranial hypertension in cystinosis

OBJECTIVES

To report a high frequency of idiopathic intracranial hypertension (IIH) in patients with cystinosis and to speculate on the relationship between these two disorders.

STUDY DESIGN

Retrospective case series and review of the literature regarding risk factors for the development of IIH in cystinosis.

RESULTS

Eight patients with cystinosis had documented papilledema, normal neuroimaging of the brain, cerebrospinal fluid (CSF) opening pressure greater than 200 mm of H2O, and normal CSF composition. No common medication, condition, or disease except cystinosis was found in these persons. Six of the patients had received prednisone, growth hormone, cyclosporine, oral contraceptives, vitamin D, or levothyroxine at the time of onset of IIH. Five patients had previous renal transplants.

CONCLUSION

No single risk factor for the development of IIH linked IIH to cystinosis in our patients. However, thrombosis susceptibility as a result of renal disease or impaired CSF reabsorption in the arachnoid villi as a result of cystine deposition might lead to the development of IIH in cystinosis.

Early oral cysteamine therapy for nephropathic cystinosis

Nephropathic cystinosis is an autosomal recessive lysosomal storage disorder in which intracellular cystine accumulates due to impaired transport out of lysosomes. The clinical manifestations include renal tubular Fanconi syndrome in the 1st year of life, with hypophosphatemic rickets, hypokalemia, polyuria, dehydration and acidosis, growth retardation, hypothyroidism, photophobia, renal glomerular deterioration by 10 years of age, and late complications such as myopathy, pancreatic insufficiency, and retinal blindnesss. The cystinosis gene, CTNS, codes for cystinosin, a 367 amino acid protein with seven transmembrane domains. More than 50 CTNSmutations have been identified, but approximately 50% of Northern European patients have a 57257-bp deletion which removes the first nine exons of CTNS. The mainstay of cystinosis therapy is oral cysteamine (Cystagon). This aminothiol can lower intracellular cystine content by 95%, and has proven efficacy in delaying renal glomerular deterioration, enhancing growth, preventing hypothyroidism, and lowering muscle cystine content. Its early and diligent use is critical; in one study, for every month of treatment prior to 3 years of age, 14 months' worth of later renal function were preserved. Several examples of individual patients treated early and having preserved renal function and normal growth are available. Newborn screening using a chip containing cDNA to detect common CTNSmutations may allow diagnosis and treatment in the first weeks of life.

CONCLUSIONS

Early diagnosis and treatment of nephropathic cystinosis can change the course of this disease.

Osteopenia and fractures in cystinotic children post renal transplantation

Many of the end-organ effects of cystinosis are known to be risk factors for osteopenia; these include deposition of cystine crystals in bone, hypothyroidism, diabetes mellitus, primary hypogonadism, urinary phosphate wasting, and chronic renal failure. While transplantation may correct the latter, it exposes the child to other risk factors for diminished bone mass, notably the use of high-dose glucocorticoids. Our objective was to determine if these multiple risk factors translate into an increased occurrence of osteopenia, as measured by dual-energy X-ray absorptiometry (DEXA), and/or fractures in this population. We examined the charts, X-rays, and bone mineral density (BMD) of all cystinotic patients post renal transplant for whom this information was available. Lumbar spine BMD was measured by DEXA scan (Hologic 4500). Z-scores were corrected for growth parameters using previously published reference data. Fracture history and pertinent serum markers of bone metabolism were also analyzed. Of the 63 renal transplants performed at our institution, 11 children were transplanted due to cystinosis. Nine of these patients, 5 male and 4 female, had had BMD evaluations, with an average age of 14.3 years (range 5-17 years) at the time of initial BMD post transplant. The mean interval between transplant and BMD evaluation was 39 months (range 3-90 months). Surprisingly, 7 of 9 patients had normal uncorrected BMD values (z-scores -1.92 to +0.02) and 7 of 9 patients had normal corrected values (z-scores -1.20 to +1.93). Three patients suffered from a total of eight fractures. Of the 3 fracture patients, 2 had normal BMD. All patients maintained good graft function and had normal calcium/phosphate mineral status. Of note, 3 of 5 male patients had evidence of primary testicular failure at earlier ages than often described, and this may be an unrecognized risk factor for bone disease in this population. Despite the numerous risk factors for developing osteopenia, these results suggest that the majority of cystinotic patients post renal transplant do not experience reduced bone mineral content as measured by DEXA. However, the significant fracture history among these patients demonstrates that DEXA cannot be used to assess fracture risk in patients with nephropathic cystinosis.

A multicentre randomised double masked clinical trial of a new formulation of topical cysteamine for the treatment of corneal cystine crystals in cystinosis

AIM

To evaluate the safety and efficacy of a new topical cysteamine formulation, stable at room temperature, for the treatment of corneal cystine crystals in cystinosis.

METHODS

20 study subjects were enrolled in the safety study and 16 in the efficacy study. Both studies were randomised and double blind. The primary outcome for the safety study was the occurrence of predefined serious adverse reactions over 6 months and for the efficacy study the reduction of corneal cystine crystal score (CCCS) by 1.00 or more units on photographs graded by a reading centre using a standardised protocol.

RESULTS

No study subject developed any serious adverse reactions. In the efficacy study, 47% of eyes receiving the standard formulation experienced a reduction in the CCCS of >/=1.00 after 1 year, while 7% of eyes on the new formulation experienced such a decrease (p=0.04).

CONCLUSION

Although no serious adverse reactions were observed with either formulation, the new formulation was not as effective as the standard formulation.

The promoter of a lysosomal membrane transporter gene, CTNS, binds Sp-1, shares sequences with the promoter of an adjacent gene, CARKL, and causes cystinosis if mutated in a critical region

Although >55 CTNS mutations occur in patients with the lysosomal storage disorder cystinosis, no regulatory mutations have been reported, because the promoter has not been defined. Using CAT reporter constructs of sequences 5' to the CTNS coding sequence, we identified the CTNS promoter as the region encompassing nucleotides -316 to +1 with respect to the transcription start site. This region contains an Sp-1 regulatory element (GGCGGCG) at positions -299 to -293, which binds authentic Sp-1, as shown by electrophoretic-mobility-shift assays. Three patients exhibited mutations in the CTNS promoter. One patient with nephropathic cystinosis carried a -295 G-->C substitution disrupting the Sp-1 motif, whereas two patients with ocular cystinosis displayed a -303 G-->T substitution in one case and a -303 T insertion in the other case. Each mutation drastically reduced CAT activity when inserted into a reporter construct. Moreover, each failed either to cause a mobility shift when exposed to nuclear extract or to compete with the normal oligonucleotide's mobility shift. The CTNS promoter region shares 41 nucleotides with the promoter region of an adjacent gene of unknown function, CARKL, whose start site is 501 bp from the CTNS start site. However, the patients' CTNS promoter mutations have no effect on CARKL promoter activity. These findings suggest that the CTNS promoter region should be examined in patients with cystinosis who have fewer than two coding-sequence mutations.

Pulmonary dysfunction in adults with nephropathic cystinosis

OBJECTIVE

To characterize the pulmonary dysfunction in patients with nephropathic cystinosis after renal transplantation.

DESIGN

Cross-sectional analysis of consecutive adult patients.

PATIENTS

Twelve adult, nephropathic cystinosis patients and 3 adult, ocular, nonnephropathic cystinosis patients admitted to the National Institutes of Health Clinical Center.

RESULTS

The 12 nephropathic cystinosis patients (age range, 21 to 40 years) showed an extraparenchymal pattern of restrictive lung disease, with inspiratory and expiratory dysfunction. Specifically, the mean FVC was 58% of predicted, the mean FEV(1) was 57% of predicted, and the mean total lung capacity was 66% of predicted, while the mean residual volume was normal. Furthermore, the mean maximal inspiratory pressure for the eight patients tested was 40% of predicted, and the mean maximal expiratory pressure was 26% of predicted. Two patients died of respiratory insufficiency. All the patients had lived at least 17 years, while lacking compliant cystine-depleting therapy with oral cysteamine. Seven patients had a conical chest, restricting excursion, and 10 of the 12 patients had evidence of the myopathy that typifies late cystinosis. In fact, the severity of pulmonary disease correlated directly with the severity of myopathy in our group of 12 patients. In contrast, the lung parenchyma was essentially normal, as gauged by chest radiographs and CT scans of the lung. The three patients with nonnephropathic cystinosis displayed entirely normal pulmonary function.

CONCLUSION

The distal myopathy characteristic of nephropathic cystinosis results in an extraparenchymal pattern of restrictive lung disease in adults who have not received long-term cystine depletion. Whether or not oral cysteamine therapy can prevent this complication remains to be determined.

Corneal crystals in nephropathic cystinosis: natural history and treatment with cysteamine eyedrops

Although renal disease is the most prominent feature of the lysosomal storage disease cystinosis, corneal cystine crystal formation remains a major complication, leading to photophobia, corneal erosions, and keratopathies. Moreover, the extent of corneal crystal accumulation reflects the course and severity of the disease itself, and the cornea is accessible to direct examination. Therefore, we employed a scoring system, based on a library of slit-lamp photographs of corneas with increasing crystal densities (0.00-3.00), to assess the degree of crystal accumulation in 170 patients with nephropathic cystinosis examined at the National Institutes of Health between 1976 and 2000. None of the patients had received topical cystine-depleting therapy at the time of the evaluation. In this natural history study, infants in the first year of life had absent or minimal corneal crystals, i.e., a corneal cystine crystal score (CCCS) of 0 or 0.25. However, the CCCS increased linearly with age, such that every patient had visible crystals by 16 months of age, and plateaued at approximately 3.00 by early adolescence. Longitudinal studies in representative patients support the cross-sectional results. Individuals homozygous for the common 57-kb deletion involving the cystinosis gene (CTNS) displayed the same course of corneal crystal accumulation as did individuals not bearing the large deletion. Patients with ocular or nonnephropathic cystinosis had CCCSs that were, in general, half those expected for patients with nephropathic cystinosis of the same age. Administration of 0.55% cysteamine eyedrops, given 6 to 12 times per day, dissolved corneal cystine crystals in 10 representative patients with nephropathic cystinosis aged 1 to 32 years within 8 to 41 months.

The genomic region encompassing the nephropathic cystinosis gene (CTNS): complete sequencing of a 200-kb segment and discovery of a novel gene within the common cystinosis-causing deletion

Nephropathic cystinosis is an autosomal recessive disorder caused by the defective transport of cystine out of lysosomes. Recently, the causative gene (CTNS) was identified and presumed to encode an integral membrane protein called cystinosin. Many of the disease-associated mutations in CTNS are deletions, including one >55 kb in size that represents the most common cystinosis allele encountered to date. In an effort to determine the precise genomic organization of CTNS and to gain sequence-based insight about the DNA within and flanking cystinosis-associated deletions, we mapped and sequenced the region of human chromosome 17p13 encompassing CTNS. Specifically, a bacterial artificial chromosome (BAC)-based physical map spanning CTNS was constructed by sequence-tagged site (STS)-content mapping. The resulting BAC contig provided the relative order of 43 STSs. Two overlapping BACs, which together contain all of the CTNS exons as well as extensive amounts of flanking DNA, were selected and subjected to shotgun sequencing. A total of 200,237 bp of contiguous, high-accuracy sequence was generated. Analysis of the resulting data revealed a number of interesting features about this genomic region, including the long-range organization of CTNS, insight about the breakpoints and intervening DNA associated with the common cystinosis-causing deletion, and structural information about five genes neighboring CTNS (human ortholog of rat vanilloid receptor subtype 1 gene, CARKL, TIP-1, P2X5, and HUMINAE). In particular, sequence analysis detected the presence of a novel gene (CARKL) residing within the most common cystinosis-causing deletion. This gene encodes a previously unknown protein that is predicted to function as a carbohydrate kinase. Interestingly, both CTNS and CARKL are absent in nearly half of all cystinosis patients (i.e., those homozygous for the common deletion). [The sequence data described in this paper have been submitted to the GenBank data library under accession nos. AF168787 and AF163573.]

Ocular nonnephropathic cystinosis: clinical, biochemical, and molecular correlations

Ocular nonnephropathic cystinosis, a variant of the classic nephropathic type of cystinosis, is an autosomal recessive lysosomal storage disorder characterized by photophobia due to corneal cystine crystals but absence of renal disease. We determined the molecular basis for ocular cystinosis in four individuals. All had mutations in the cystinosis gene CTNS, indicating that ocular cystinosis is allelic with classic nephropathic cystinosis. The ocular cystinosis patients each had one severe mutation and one mild mutation, the latter consisting of either a 928 G-->A (G197R) mutation or an IVS10-3 C-->G splicing mutation resulting in the insertion of 182 bp of IVS10 into the CTNS mRNA. The mild mutations appear to allow for residual CTNS mRNA production, significant amounts of lysosomal cystine transport, and lower levels of cellular cystine compared with those in nephropathic cystinosis. The lack of kidney involvement in ocular cystinosis may be explained by two different mechanisms. On the one hand (e.g. the G197R mutation), significant residual cystinosin activity may be present in every tissue. On the other hand (e.g. the IVS 10-3 C-->G mutation), substantial cystinosin activity may exist in the kidney because of that tissue's specific expression of factors that promote splicing of a normal CTNS transcript. Each of these mechanisms could result in minimally reduced lysosomal cystine transport in the kidneys.

A randomized clinical trial of topical cysteamine disulfide (cystamine) versus free thiol (cysteamine) in the treatment of corneal cystine crystals in cystinosis

In nephropathic cystinosis, corneal cystine crystals cause severe photophobia and corneal erosions. Topical cysteamine dissolves these crystals, but cannot be marketed because it rapidly oxidizes to the disulfide form, cystamine, at room temperature. Since cystamine itself could be used commercially, we compared the efficacy of cystamine and cysteamine with respect to cystine crystal dissolution in a randomized, double-masked clinical trial. One eye each of 14 patients with cystinosis was randomized to either cystamine or cysteamine, 0.5%, with 0.01% benzalkonium chloride; the companion eye was treated with the alternate preparation. Corneal crystals were photographed and a density score was assigned to each slide based on 13 standard slides. After 8-20 months, 6 patients showed significant reduction of the corneal crystal score in only one eye. In each case, the improved eye was the cysteamine-treated eye. Theoretically, cysteamine should dissolve both intracellular and extracellular crystals, whereas cystamine should dissolve only intracellular crystals because it must first be reduced to the free thiol by the cytoplasmic-reducing environment. Hence, the lack of efficacy of the disulfide cystamine suggests that some corneal cystine crystals in cystinosis patients are extracellular, and that another form of stable, topical cysteamine must be developed for cystinosis patients.

A cost-effectiveness analysis of the orphan drug cysteamine in the treatment of infantile cystinosis

OBJECTIVE

Cysteamine is a recently licensed orphan drug used to treat the inherited metabolic disease cystinosis. The drug delays the onset of renal failure in cystinotic patients and may provide many other significant health benefits. This study examined the cost-effectiveness of the administration of cysteamine to cystinotic patients prior to end-stage renal disease (ESRD).

METHOD

Decision-tree analysis and cost-effectiveness analysis. Cost data were estimated from current clinical charges and Medicare public-access reports. Life expectancy outcomes were derived from both published and unpublished clinical studies and from the U.S. Renal Data System.

RESULTS

Cysteamine therapy can extend the life of kidneys and delay renal transplantation, thereby increasing life expectancy for patients with cystinosis. Patients receiving cysteamine therapy prior to renal failure have lifetime-treatment drug costs of $234,000, in comparison with $238,000 for those who are not medicated. Costs of cysteamine therapy are offset by savings associated with delaying transplantation and costs of dialysis.

CONCLUSIONS

Use of the orphan drug cysteamine both improves health outcomes and reduces health care costs for patients with cystinosis.

Cystinosis and gingival hyperplasia: demonstration of cystine crystals in gingival tissue and unusual aspects of management

A patient with nephropathic cystinosis developed gingival hyperplasia secondary to cyclosporine-A therapy for his renal allograft. The typical crystals described on electron microscopic examination of other organs of patients with cystinosis were seen in the resected gingiva of this patient. These crystals have not been previously described in this location. Unusual aspects of the management of this patient are discussed.

Distal vacuolar myopathy in nephropathic cystinosis

Nephropathic cystinosis is a lysosomal storage disorder leading to renal failure by age 10 years. Prolonged patient survival following renal transplantation has allowed the development of previously unknown long-term complications. Muscle involvement has been reported in a single posttransplant cystinosis patient, but the range of clinical, electrophysiologic, and histologic features has not been fully described. Thirteen of 54 post-renal-transplant patients that we examined developed weakness and wasting in the small hand muscles, with or without facial weakness and dysphagia. Tendon reflexes were preserved and sensory examinations were normal. Electrophysiologic studies in 11 affected patients showed normal nerve conduction velocities and preserved sensory action potentials. The voluntary motor units in the affected distal muscles had reduced amplitude and brief duration, confirmed with quantitative electromyography in 4 patients. Biopsy of the severely affected abductor digiti minimi or extensor carpi radialis brevis muscles in 2 patients revealed marked fiber size variability, prominent acid phosphatase-positive vacuoles, and absence of fiber type grouping or inflammatory cells. Crystals of cystine were detected in perimysial cells but not within the muscle cell vacuoles. The muscle cystine content of clinically affected muscles was markedly elevated. We conclude that a distal vacuolar myopathy is a common late complication of untreated nephropathic cystinosis. Although the cause is unclear, the general lysosomal defect in this disease may also affect the lysosomes within muscle fibers.

Improved renal function in children with cystinosis treated with cysteamine

BACKGROUND

The lysosomal storage disease cystinosis results in renal failure at approximately 10 years of age. Although oral cysteamine therapy is recognized to preserve kidney function, the extent of renal benefit has not been determined.

METHODS

Between 1960 and 1992, we determined 24-hour creatinine clearances in 76 children with cystinosis during 1081 admissions to the National Institutes of Health. Seventeen children were considered to have received adequate treatment with cysteamine, since they had depletion of cystine from leukocytes and began therapy before the age of 2 years; treatment lasted a mean of 7.1 years. Thirty-two children were considered to have received partial treatment, since they had poor compliance with therapy or began treatment after the age of 2; treatment lasted a mean of 4.5 years. Twenty-seven children were followed in the era before cysteamine therapy and thus never received cysteamine.

RESULTS

Of the 27 children who never received cysteamine, 16 were followed at the National Institutes of Health until renal failure occurred; their mean (+/- SD) creatinine clearance was 8.0 +/- 4.8 ml per minute per 1.73 m2 of body-surface area at a mean age of 8.3 +/- 1.9 years. Of the 17 children who received adequate treatment, none had renal failure; their mean creatinine clearance was 57 +/- 20 ml per minute per 1.73 m2 at 8.3 +/- 3.8 years of age. The mean creatinine clearance of the children who received partial or adequate treatment with cysteamine increased with age up to the age of five years and then declined linearly with age at a normal rate. For the children who received adequate treatment, the mean creatinine clearance was predicted to reach 0 ml per minute per 1.73 m2 at the age of 74 years, as compared with 20 years of age for the children who received partial treatment. With no therapy, the mean creatinine clearance reaches 0 ml per minute per 1.73 m2 at 10 years of age.

CONCLUSIONS

Children with cystinosis who are treated early and adequately with cysteamine have renal function that increases during the first five years of life and then declines at a normal rate. Patients with poorer compliance and those who are treated at an older age do less well.

Growth and pubertal development in nephropathic cystinosis

In a retrospective investigation growth and pubertal development were evaluated in 30 patients with nephropathic cystinosis. Growth was investigated during the stage of chronic renal insufficiency as well as after successful kidney transplantation and growth rates were related to kidney function. Pubertal development was evaluated in 17 patients between 12 and 25 years of age. Prepubertal growth rates were stable in a range between -2 and -3 height velocity SDS as long as glomerular filtration rate was above 20ml/min per 1.73m2. A decrease in glomerular filtration rate below this threshold was followed by further decrease in height velocity. After kidney transplantation a significant catch-up growth was seen if immunosuppression was performed with cyclosporine A and low dose prednisolone. This did not occur if conventional therapy with azathioprine and high-dose prednisolone was used. Onset of puberty was delayed in all patients. Gonadotropin and oestradiol levels in female patients showed normal fluctuations according to ovulatory cycles. In male patients after puberty there was an increase in gonadotropin levels above the normal range for adult men while testosterone levels remained in the low normal range. These results indicate that adult men with nephropathic cystinosis may develop hypergonadotropic hypogonadism.

Parenchymal organ cystine depletion with long-term cysteamine therapy

Nephropathic cystinosis is a lysosomal storage disorder characterized by renal failure, multisystem organ damage, and poor growth. Oral cysteamine therapy retards renal deterioration and enhances growth, but parenchymal organ cystine depletion has never been documented. We measured skeletal muscle cystine in 11 cystinosis patients not treated with cysteamine; analysis of their values plus 11 published values showed that muscle cystine increases linearly with age in cystinosis patients (slope, 0.074 nmol half-cystine/mg wet wt/year). In contrast, 15 patients treated for 4 to 11 years with oral cysteamine had a relatively constant muscle cystine content (slope, 0.004 nmol half-cystine/mg wet wt/year). The treated patients' mean muscle cystine, 0.091 +/- 0.064 (SD) nmol half-cystine/mg wet wt, was significantly less (P < 0.001) than that for the 11 youngest untreated patients, 0.754 +/- 0.534 nmol half-cystine/mg wet wt. On postmortem examination, a 9-year-old cystinosis patient treated for 8 years with oral cysteamine had liver, kidney, pancreas, lung, and spleen cystine values 5 to 90 times lower than those of an untreated age-matched control. We conclude that long-term oral cysteamine therapy routinely depletes cystinotic skeletal muscle of cystine; cysteamine is the treatment of choice for the prevention of both renal and nonrenal complications of cystinosis.

Effects of oral phosphocysteamine and rectal cysteamine in cystinosis

Diurnal variation in leucocyte cystine and the effects of equimolar single doses of oral phosphocysteamine and rectal cysteamine were studied in eight patients with cystinosis, aged 1.8-16.5 years. No significant diurnal variation in leucocyte cystine was found. Absorption of cysteamine was reduced after rectal administration compared with the oral dose: mean (SD) peak concentration 17.2 (6.3) mumol/l v 36.4 (5.5) mumol/l at 40 min and mean (SD) area under the curve 22.3 (14.3) v 59.4 (33.1) mumol/h/l. Oral phosphocysteamine significantly reduced the mean (SD) leucocyte cystine from 8.09 (0.47) to 3.26 (1.48) nmol 1/2 cystine/mg protein at three hours. At 12 hours the mean leucocyte cystine was significantly lower than the pretreatment concentration. Rectal cysteamine did not significantly reduce the mean leucocyte cystine concentration. In conclusion, phosphocysteamine suspension may be administered every 12 hours. Rectal cysteamine administration is feasible but higher doses are required before efficacy can be judged.

Renal transplantation in 22 children with nephropathic cystinosis

In 1989, 22 children (11 boys, 11 girls aged 8-23 years) with nephropathic cystinosis, who had received a total of 28 renal allografts over the previous 14 years, were reviewed. Nineteen were alive, of whom 17 had functioning grafts 5 months to 13 years after transplantation. The mean serum creatinine level in these 17 was 135 mumol/l. Patient and graft survival did not differ from non-cystinotic children. Persistent hypothyroidism was found in 3 patients, transient diabetes mellitus in 1, severely disturbed vision in 1 and brain atrophy in 11. Arterial hypertension was present in 16 patients. Growth retardation was universal, although in 4 patients on cyclosporin A post-transplant catch-up growth occurred. Five patients over 15 years completed puberty. Readjustment in terms of school performance was good but was less good for psychosocial development. None of the patients had ever been treated with cystine-depleting agents; the data will therefore provide a historical control group with which to compare the results from a group treated with these agents.

Update on nephropathic cystinosis

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

Swallowing dysfunction in nephropathic cystinosis

BACKGROUND

Nephropathic cystinosis causes renal failure in most patients at approximately 10 years of age. This can be prevented or retarded by cystine-depleting therapy with oral cysteamine. Many patients who do not receive adequate cysteamine therapy undergo renal transplantation, but the accumulation of cystine continues in other organs, resulting in various clinical abnormalities. We report age-related swallowing dysfunction in patients with nephropathic cystinosis.

METHODS

We studied 43 patients with cystinosis (24 who had received a renal transplant and 19 who had not), 3 to 31 years of age. Oral motor function was assessed by a cranial-nerve oral sensorimotor examination, and an oral motor index was calculated for each patient. The oral phase of swallowing was assessed by ultrasonography, and the pharyngeal and esophageal phases were evaluated by videofluoroscopy.

RESULTS

Approximately half the patients were slow eaters. Oral motor dysfunction, reflected by a higher oral motor index, increased with age. Speech, oral structure and anatomy, and tongue and lip strength were particularly affected. Seven of nine patients 21 to 31 years old had abnormalities in all three phases of swallowing; the deficits were variable in younger patients. In 28 patients with cystinosis, the mean (+/- SD) duration of oropharyngeal swallowing for a dry swallow (3.06 +/- 1.06 seconds) was longer than in 14 normal subjects (1.89 +/- 0.57 seconds; P less than 0.001). This prolongation reflected impairment of the initiation phase of swallowing.

CONCLUSIONS

Swallowing dysfunction is a late complication of nephropathic cystinosis, probably related to muscular dysfunction. Changes in the consistency of foods, swallowing exercises, and long-term cysteamine therapy should be considered for patients with cystinosis who have difficulty in swallowing.

Predicted reciprocal serum creatinine at age 10 years as a measure of renal function in children with nephropathic cystinosis treated with oral cysteamine

The predicted reciprocal creatinine at age 10 years (PRC10), a parameter of renal function based upon the linear relationship between reciprocal serum creatinine and age, incorporates age, serum creatinine, and rate of renal deterioration into a single term. PRC10 measurements were employed to assess renal function in children with nephropathic cystinosis treated with oral cysteamine, a cystine-depleting agent. In 71 children receiving oral cysteamine for at least 1 year, PRC10 decreased linearly with initial serum creatinine concentration. This indicated that, although established renal damage in cystinosis was irreversible, early intervention with cysteamine therapy could favorably alter the rate of glomerular deterioration. In other analyses, mean PRC10 was shown to increase with duration of cysteamine therapy and extent of leukocyte cystine depletion. The predicted reciprocal creatinine value at a certain age can be useful in analyzing the effects of therapeutic intervention in a disease with a relatively uniform rate of renal deterioration.