Cognition in nephropathic cystinosis: pattern of expression in heterozygous carriers

Cognitive functions and behavioural profiles in children with cystinosis treated with cysteamine and correlation with treatment duration

Background

Cystinosis is a rare autosomal recessive disease. Children with nephropathic cystinosis (NCTN) have evidence of intellectual dysfunction and behavioural abnormalities which are attributed to renal dysfunction, metabolic disarrangement, and gene mutation. This study aimed to characterize the cognitive functions and behavioural profiles in nephropathic cystinosis patients on cysteamine therapy, and determine its relation to cysteamine treatment duration. In this analytical cohort study, 20 children with nephropathic cystinosis aged 6 years or above were compared to 26 children with chronic kidney disease (CKD) matched in age, sex, and CKD stage. All patients were subjected to full clinical and psychometric assessment using the Child Behaviour Checklist (CBCL) and the Arabic language version of Stanford-Binet test (SB).

Results

There was no significant difference between both groups regarding Stanford-Binet test (SB) and Child Behavioural Checklist (CBCL), apart from delinquent behaviour. Duration of cysteamine treatment was inversely correlated with short-term memory, thought, and sex problems.

Conclusions

Children with cystinosis have a wide range of neurocognitive and behavioural problems that still present after cysteamine treatment and may be related to impact of genetic mutation on brain structure and function. Longer duration of cysteamine treatment could have beneficial effects on some behavioural problems.

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.

Visual and verbal learning and memory in cystinosis

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

Hierarchical processing of visual stimuli in nephropathic cystinosis

Previous studies have shown that individuals with cystinosis may exhibit difficulty with visuospatial tasks. Global and local (hierarchical) processing are specific types of visuospatial tasks mediated by the right and left parietal lobes respectively. The study objective was to determine whether individuals with cystinosis and carriers of the cystinosin gene mutation show deficits in global and/or local processing. The study included 48 children (32 controls, 16 cystinosis) and 56 adults (25 controls, 25 carriers, and 6 cystinosis). Participants were instructed to replicate 10 hierarchical stimuli to assess global-local processing. The primary outcome measure was mean global and local performance on the hierarchical stimuli task between subgroups. Error subtypes were included to further assess each image. Compared to the control subgroups, adult and child cystinosis patients as well adult carriers demonstrated significant deficits in the global processing of a hierarchical stimulus against a background of unimpaired local processing. Child cystinosis patients performed significantly more poorly than controls on all error subtypes except local shape distortion. Adult cystinosis patients and carriers made significantly more global shape distortion errors than the controls. Our study shows that the cognitive profile documented in cystinosis patients and carriers includes significant difficulties with the global processing of an image. Results of the carrier population are important since they suggest that the cognitive impairments observed in patients cannot be attributed to symptomatic manifestations of the disease. Instead, the global processing deficits observed provide insight into the potential role of the cystinosin gene mutation on neurodevelopmental differences seen in these individuals.