The developmental cognitive trajectory of the 22Q11.2 deletion

Background: The 22q11.2 deletion (22qDS) is a microdeletion syndrome which commonly leads to an uneven profile of Learning difficulties (LD), with superior verbal compared to nonverbal intellectual and memory functions in children and adolescents. However, in adult samples these differences reduce. There are two accounts of the reduction in the verbal-nonverbal discrepancy with age. The dominant hypothesis is that normative measures of verbal intelligence decline and so approximate nonverbal intelligence. The other is that normative nonverbal intelligence increases while verbal intelligence remains stable. Few studies have investigated this longitudinally and none with a UK sample. Aim: The aim was to examine longitudinally the pattern of developmental cognitive changes in verbal and nonverbal intellectual and memory functions. Method: Twenty-four participants with 22qDS, who were previously cognitively assessed between 2004- 2008 were re-examined in 2011. Intellectual, memory and executive functions were assessed. Results: Verbal and nonverbal intellectual functions were in the below average range and verbal was significantly superior to nonverbal intelligence at initial assessment. This discrepancy disappeared at follow-up as expected. Contrary to the dominant hypothesis, no cognitive scores declined with age. Nonverbal intellectual functioning improved to approximate the original level of verbal functioning, which remained stable. There were no verbal-nonverbal discrepancies in memory, but there were unexpected gender effects. Conclusion: This is the first longitudinal study to show increasing nonverbal and stable verbal functioning with age in a UK 22qDS sample. Factors which could potentially account for this unexpected pattern are considered along with bias, confounding and other methodological issues. The potential clinical and educational implications of the findings are discussed. Further studies with large samples are required to examine in more detail the main findings.