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

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.

Response inhibition and error-monitoring in cystinosis (CTNS gene mutations): Behavioral and electrophysiological evidence of a diverse set of difficulties

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. Behaviorally, some deficits in executive function have been noted in this population, but the underlying neural processes are not understood. Using standardized cognitive assessments and a Go/No-Go response inhibition task in conjunction with high-density electrophysiological recordings (EEG), we sought to investigate the behavioral and neural dynamics of inhibition of a prepotent response and of error monitoring (critical components of executive function) in individuals with cystinosis, when compared to age-matched controls. Thirty-seven individuals diagnosed with cystinosis (7-36 years old, 24 women) and 45 age-matched controls (27 women) participated in this study. Analyses focused on N2 and P3 No-Go responses and error-related positivity (Pe). Atypical inhibitory processing was shown behaviorally. Electrophysiological differences were additionally found between the groups, with individuals with cystinosis showing larger No-Go P3s. Error-monitoring was likewise different between the groups, with those with cystinosis showing reduced Pe amplitudes.

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.

Neuropsychological and neuroanatomical phenotype in 17 patients with cystinosis

Background

Cystinosis is a rare autosomal recessive disorder caused by intracellular cystine accumulation. Proximal tubulopathy (Fanconi syndrome) is one of the first signs, leading to end-stage renal disease between the age of 12 and 16. Other symptoms occur later and encompass endocrinopathies, distal myopathy and deterioration of the central nervous system. Treatment with cysteamine if started early can delay the progression of the disease. Little is known about the neurological impairment which occurs later. The goal of the present study was to find a possible neuroanatomical dysmorphic pattern that could help to explain the cognitive profile of cystinosis patients. We also performed a detailed review of the literature on neurocognitive complications associated with cystinosis.

Methods

17 patients (mean age = 17.6 years, [5.4–33.3]) with cystinosis were included in the study. Neuropsychological assessment was performed including intelligence (Intelligence Quotient (IQ) with Wechsler’s scale), memory (Children Memory Scale and Wechsler Memory Scale), visuo-spatial (Rey’s figure test) and visuo-perceptual skills assessments. Structural brain MRI (3 T) was also performed in 16 out of 17 patients, with high resolution 3D T1-weighted, 3D FLAIR and spectroscopy sequences.

Results

Intellectual efficiency was normal in patients with cystinosis (mean Total IQ = 93). However the Perceptual Reasoning Index (mean = 87, [63–109]) was significantly lower than the Verbal Comprehension Index (mean = 100, [59–138], p = 0.003). Memory assessment showed no difference between visual and verbal memory. But the working memory was significantly impaired in comparison with the general memory skills (p = 0.003). Visuospatial skills assessment revealed copy and reproduction scores below the 50th percentile rank in more than 70% of the patients. Brain MRI showed cortical and sub-cortical cerebral atrophy, especially in the parieto-occipital region and FLAIR hypersignals in parietal, occipital and brain stem/cerebellum. Patients with atrophic brain had lower Total IQ scores compared to non-atrophic cystinosis patients.

Conclusions

Patients with cystinosis have a specific neuropsychological and neuroanatomical profile. We suggest performing a systematic neuropsychological assessment in such children aiming at considering adequate management.

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.

Differential gene expression in patients with subsyndromal symptomatic depression and major depressive disorder

Background

Subsyndromal symptomatic depression (SSD) is a subtype of subthreshold depressive and can lead to significant psychosocial functional impairment. Although the pathogenesis of major depressive disorder (MDD) and SSD still remains poorly understood, a set of studies have found that many same genetic factors play important roles in the etiology of these two disorders. Nowadays, the differential gene expression between MDD and SSD is still unknown. In our previous study, we compared the expression profile and made the classification with the leukocytes by using whole-genome cRNA microarrays among drug-free first-episode subjects with SSD, MDD and matched healthy controls (8 subjects in each group), and finally determined 48 gene expression signatures. Based on these findings, we further clarify whether these genes mRNA was different expressed in peripheral blood in patients with SSD, MDD and healthy controls (60 subjects respectively)

Method

With the help of the quantitative real-time reverse transcription-polymerase chain reaction (RT-qPCR), we gained gene relative expression levels among the three groups.

Results

We found that there are three of the forty eight co-regulated genes had differential expression in peripheral blood among the three groups, which are CD84, STRN, CTNS gene (F = 3.528, p = 0.034; F = 3.382, p = 0.039; F = 3.801, p = 0.026, respectively) while there were no significant differences for other genes.

Conclusion

CD84, STRN, CTNS gene may have significant value for performing diagnostic functions and classifying SSD, MDD and healthy controls.

Executive function in nephropathic cystinosis

OBJECTIVE

We studied executive function (EF) in children and adolescents with cystinosis.

BACKGROUND

Cystinosis is a genetic metabolic disorder in which the amino acid cystine accumulates in all organs of the body, including the brain. Previous research has shown that individuals with cystinosis have visuospatial deficits, but normal intelligence and intact verbal abilities. Better understanding of the behavioral phenotype associated with cystinosis could have important implications for treatment.

METHODS

Twenty-eight children with cystinosis and 24 control participants (age range 8 to 17 years) underwent selected Delis-Kaplan executive function system tests for neuropsychological assessment of EF, and the participants' parents completed the behavior rating inventory of executive function.

RESULTS

Participants with cystinosis performed significantly more poorly than controls on all Delis-Kaplan Executive Function System indices examined and on the behavior rating inventory of executive function metacognition index and global executive composite.

CONCLUSIONS

EF is an area of potential risk in cystinosis. Our data have implications not only for the function of affected children and adolescents in school and daily life, but also for disease management and treatment adherence. Our findings can aid in the design and implementation of interventions and lead to a greater understanding of brain-behavior relationships in cystinosis.

Cognition in nephropathic cystinosis: pattern of expression in heterozygous carriers

Individuals with cystinosis exhibit specific cognitive deficits in visual spatial function. The purpose of the current study was to examine if obligate heterozygotes of the CTNS mutation have the same pattern of cognitive functioning seen in homozygotes, namely aberrant visual-spatial functioning against a background of relatively intact visual-perceptual functioning and overall cognitive ability. Study participants were 254 adults (100 heterozygotes and 154 controls), ages 17 years 10 months through 74 years 9 months. Tests of intelligence, visual perceptual, and visual spatial functioning were administered. Our results showed that cystinosis heterozygotes demonstrated intelligence within the normal range, and performed similarly to controls on tests of visual-perceptual ability. In contrast, the heterozygotes performed significantly more poorly on each of the visual-spatial tests when compared to controls. Obligate heterozygotes for the CTNS mutation display a similar pattern of visual processing decrements as do individuals with cystinosis. Namely, carriers demonstrate relative weaknesses in visual-spatial processing, while maintaining normal visual perceptual ability and intelligence in the normal range. The visual spatial decrements in heterozygotes were not as marked as those found in individuals with cystinosis, suggesting a gene dosing effect. This study provides an impetus for other studies of gene-behavior relationships in recessive disorders, and may stimulate further interest in the role of aberrant genes on "individual differences" in behavior.

Neurocognitive functioning in school-aged cystinosis patients

INTRODUCTION

Cystinosis is an autosomal recessive disorder leading to intralysosomal cystine accumulation in various tissues. It causes renal Fanconi syndrome and end stage renal failure around the age of 10 years if not treated with cysteamine. Children with cystinosis seem to have a normal intelligence but frequently show learning difficulties. These problems may be due to specific neurocognitive deficits rather than impaired renal function. Whether cysteamine treatment can improve cognitive functioning of cystinosis patients is thus far unknown. We aim to analyze neurocognitive functioning of school-aged cystinosis patients treated with cysteamine in order to identify specific deficits that can lead to learning difficulties.

PATIENTS AND METHODS

Fourteen Dutch and Belgian school-aged cystinosis patients were included. Glomerular filtration rate was estimated using the Schwartz formula. Children were tested for general intelligence, visual-motor integration, inhibition, interference, sustained attention, accuracy, planning, visual memory, processing speed, motor planning, fluency and speed, and behavioural and emotional functioning using standardized methods.

RESULTS

Glomerular filtration rate ranged from 22 to 120 ml min(-1) 1.73 m(-2). Median full-scale intelligence was below the average of a normal population (87, range 60-132), with a discrepancy between verbal (median 95, range 60-125) and performance (median 87, range 65-130) intelligence. Over 50% of the patients scored poorly on visual-motor integration, sustained attention, visual memory, planning, or motor speed. The other tested areas showed no differences between patients' and normal values.

CONCLUSION

Neurocognitive diagnostics are indicated in cystinosis patients. Early recognition of specific deficits and supervision from special education services might reduce learning difficulties and improve school careers.

Neurological impairment in nephropathic cystinosis: motor coordination deficits

Nephropathic cystinosis is a rare genetic metabolic disorder that results in accumulation of the amino acid cystine in lysosomes due to lack of a cystine-specific transporter protein. Cystine accumulates in cells throughout the body and causes progressive damage to multiple organs, including the brain. Neuromotor deficits have been qualitatively described in individuals with cystinosis. This study quantitatively examined fine-motor coordination in individuals with cystinosis. Brain magnetic resonance imaging (MRI) scans were also performed to determine whether structural changes were associated with motor deficits. Participants were 52 children and adolescents with infantile nephropathic cystinosis and 49 controls, ages 2-17 years, divided into preacademic and school-age groups. Results indicated that both the preacademic and school-age cystinosis groups performed significantly more poorly than their matched control groups on the Motor Coordination Test. Further, the level of performance was not significantly different between the preacademic and school-age groups. There were no significant differences in motor coordination scores based on MRI findings. This is the first study to document a persistent, nonprogressive, fine-motor coordination deficit in children and adolescents with cystinosis. The fact that these difficulties are present in the preschool years lends further support to the theory that cystinosis adversely affects neurological functioning early in development. The absence of a relationship between brain structural changes and motor function suggests that an alternative cause for motor dysfunction must be at work in this disorder.

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.

Specific cognitive deficits in young children with cystinosis: evidence for an early effect of the cystinosin gene on neural function

OBJECTIVES

Infantile nephropathic cystinosis is associated with a specific cognitive deficit in visual spatial processing in older children and adults. The cause of this deficit is unknown. This study was designed to determine whether the cognitive deficit is present in young children with cystinosis, suggesting an early effect of the genetic disorder on brain development.

STUDY DESIGN

Young children (n = 25; age, 3-8 years) with cystinosis and 25 matched control subjects underwent cognitive testing, including tests of intelligence, visual perceptual, visual spatial, and visual motor functions.

RESULTS

Children with cystinosis performed significantly more poorly on tests of visual spatial and visual motor function than did control subjects. Visual perceptual abilities were equivalent in the 2 groups.

CONCLUSION

The same pattern of visual spatial deficit is present in young children with cystinosis as has previously been demonstrated in older children and adults, which suggests that there may be an influence of the cystinosis gene on brain development, rather than an adverse effect of prolonged cystine accumulation in the brain during childhood.