The primary objective of this study was to characterize the effects of the etiology of kidney failure, dialysis treatment, and sociodemographic factors on intellectual functioning in children with kidney failure. We observed variable effects of different factors on the subdomains of intellectual functioning. The etiology of kidney failure had a significant effect on processing speed, while dialysis treatment was significantly associated with reasoning domains. Additionally, we observed a significant association between ADI and working memory, as well as a significant link between race and verbal skills. These findings align with the current literature, suggesting that neurocognitive development may be disrupted in children with CKD. Furthermore, the results indicate that the impact of kidney failure on cognitive development and functioning is multifactorial and can be attributed to various factors, such as the underlying cause, medical treatments, and sociodemographic factors.
The present study expands upon the existing knowledge regarding neurocognitive functioning in pediatric CKD and provides specificity in prediction. Specifically, our findings demonstrate that when accounting for other factors, the etiology of kidney failure is significantly associated with processing speed. Patients who had CAKUT tended to have lower processing speed than patients with nephrotic syndrome. Slower processing speed has been associated with white matter and gray matter loss in some pediatric populations, such as preterm children[16, 17]. White matter loss is also associated with chronic kidney diseases in both pediatric and adult populations[18, 19]. Considering the typical onset of CAKUT during infancy, it is plausible that this condition exerts a more pronounced impact on the change of both white and gray matter compared to other etiologies of kidney failure. However, the difference in age at onset of kidney failure does not fully account for these findings, as our analysis was adjusted for age. Diminished processing speed has been found to be a predictor of reduced adaptive functioning and daily living skills in some pediatric populations[20], highlighting the importance of monitoring and ongoing support for processing speed (e.g., physical therapy, occupational therapy, and educational supports) for patients who have CAKUT and patients who develop kidney failure at an earlier age.
The findings regarding the effect of dialysis treatment on neurocognitive development were mixed. Current literature indicates that the earlier age of dialysis onset and longer time on dialysis are associated with lower neurocognitive outcomes[21–23]. In our study, dialysis emerged as a significant positive contributor only when the analysis was adjusted for other factors in the models. Since most patients with CAKUT were not on dialysis and CAKUT is a significant risk factor for neurocognitive deficits, the high prevalence of CAKUT in the non-dialysis group likely masked the association between dialysis and neurocognitive outcomes, which only became apparent on multivariable analysis. It is also possible that non-dialysis patients performed poorly on the testing due to complications of CKD, such as uremia and anemia, which are often better controlled after dialysis initiation and concomitant initiation of erythropoietin therapy. These findings highlight the potential significance of timely renal replacement therapy in pediatric kidney transplant candidates.
To our knowledge, no other study has examined the relationship between neighborhood deprivation index (i.e., ADI) and intellectual functioning in pediatric kidney transplant candidates. Our study found that neighborhood deprivation negatively predicted working memory performance. Although not specifically using ADI as a proxy for socioeconomic status (SES), a recent meta-analysis of 36 studies confirmed that lower SES is associated with lower working memory performance in the broader pediatric population[24]. Results from this study suggest that pediatric kidney transplant candidates with a socioeconomic disadvantage may benefit from additional tools and strategies to support working memory in educational and medical settings. For instance, providers could use multimodal strategies that emphasize chunking and summarizing information and provide information clearly, concisely, and repeatedly.
The present study demonstrates that race is significantly associated with the verbal comprehension domain. Specifically, White patients tended to perform higher on verbal tasks compared to patients from marginalized racial backgrounds. However, this finding is not surprising given that verbal skills are influenced by social and environmental factors and are, therefore, socially dependent competencies within IQ testing[25, 26]. Furthermore, historically marginalized racial groups experience a lack of access to resources and education to a greater degree than their white counterparts, which could subsequently impact the development of verbal skills in these groups as measured by standardized tests. It is important to consider, though, that usage-based theories purport language and verbal skills in children develop through cultural learning and interaction within a linguistic community[25]. That is, the development of verbal skills is influenced by opportunities for exposure to and use of language within specific cultural contexts for social purposes, which may not be captured in the presently used standardized assessments. Furthermore, 6% of the patients in our sample (5 out of 78) came from families where English was a second language. Individuals whose second language is English have not historically been well represented during measure standardization, which can skew how an individual’s performance is scored compared to same-aged peers. While these findings are important to situate within the broader cultural context and shortcomings of the available cognitive measures, it is still important for providers to be aware of the potential need to facilitate verbal communication and carefully consider early delays in verbal skills for children from marginalized racial backgrounds with kidney failure.
Our study had several limitations. The sample size of this study was modest as pediatric kidney failure is relatively rare[4]. As a result, it was necessary to simplify the categorization of CKD etiology and race. However, this simplification allowed us to unravel the complex interplay of factors influencing neurocognitive development in this vulnerable population. Further, we only included patients who could complete a Wechsler Intelligence Scale to allow further analysis of specific domains within intellectual functioning. Patients who were not able to complete a Wechsler Intelligence Scale in our sample were younger (i.e. preschool age), had language difficulties, or had less developed cognitive functioning. The single-center nature of this study is also a limitation. Future research should explore a multi-site design to increase the sample size and account for variations in abilities to broaden the generalizability of these findings to a broader population. Such studies would provide a more comprehensive understanding of the neurocognitive development in pediatric kidney failure and help validate the findings across different healthcare settings. This research design would also allow the exploration of additional medical variables such as the duration of illness or the age onset for kidney failure and possibly allow for further characterization of the associations between brain structure change, processing speed, and adaptive functioning in children with kidney failure.