Comparing Cognitive Functions of Children with PKU and Controls using CANTAB Nonverbal Tests

Background: Phenylketonuria is an inherited error of metabolism caused by the failure of the phenylalanine hydroxylase enzyme. In poorly-treated cases, the patients have mental retardation, psychiatric problems and skin diseases.

Objective: We aimed to examine the cognitive functions of children with PKU comparing them with age-related control patients. We examined the correlation between cognitive functions and serum Phe, Tyrosine, Phe/Tyr ratio.

Methods: The children were examined with 5 nonverbal tests of Cambridge Cambridge Neuropsychological Test Automated Battery including tests of working memory, learning and executive function; visual, verbal and episodic memory; attention, information processing and reaction time.

The data were analyzed using Microsoft Excel and R statistical packages. We used Mann-Whitney tests to compare the two groups. We normalized the results of each task and obtained a 0-10 score system to characterize the mean cognitive functions. The correlations were analysed with Spearman probes.

Results: We collected 54 children with PKU and 99 controls. We got the most explicit difference in SOC subsequent thinking time: the children with PKU were 3.12 times slower (1668 ms vs. 533,4 ms). The results show a correlation between cognitive functions with age and Phe. The mean normalized cognitive function was 5,77 in the group of children with PKU, and 7,52 in the control group.

Conclusion: Some CANTAB tests showed a significant difference between PKU and control patients – the most significant one: SOC subsequent thinking time.

According to our results, the nonverbal computer tests can be used very well to examine the fine cognitive dysfunctions caused by PKU, and it has a correlation with the serum Phe. The results confirm the importance of a strict diet.