Cognitive, behavioural and psychological functioning in Williams syndrome and Down syndrome

Studies on neuropsychological abilities in Williams syndrome (WS) and Down syndrome (DS) have typically focused on group averages, with little emphasis placed on individual performance, especially in DS. Moreover, there is little research on neuropsychological abilities in young WS children, and research on everyday executive function profiles in DS adults is also limited. In a series of five studies, this thesis examined neuropsychological functioning in WS, DS and typically developing (TD) controls across different age groups. The thesis focused on individual variability. Study 1 revealed vast heterogeneity, both in absolute levels of cognitive ability and in cognitive strengths and weaknesses, in a sample of 49 WS individuals aged 6 to 39 years. In contrast, in Study 2 there was substantial homogeneity in cognitive profiles of strengths and weaknesses on the Woodcock Johnson III Test of Cognitive Abilities, (WJ-III COG) among 24 DS adults. Specifically, while there was variability in the overall cognitive ability levels in our adult DS sample, ranging from severe impairment to low average performance, the DS adults demonstrated a flat cognitive profile, with most displaying no significant areas of cognitive strengths or weaknesses. Study 3 examined everyday executive functions in 27 DS adults (aged 22.00 to 42.00 years) using the Behaviour Rating Inventory of Executive Function—Adult Informant Version (BRIEF-A). Clinically significant elevations (impairments) were observed on almost all everyday executive functioning abilities, except on Inhibit and Emotional Control. Study 3 demonstrated variability in everyday executive functions in DS using the BRIEF-A and found no significant relationships between BRIEF-A index/scale scores and IQ. In Study 4, using parent ratings on the Child Behavior Checklist – Preschool Version (CBCL), WS preschool children (aged 2.20 to 5.97 years) demonstrated variability in some aspects of behaviour impairment/psychopathology, whereas 53 CA-matched TD control children displayed a flat behaviour/ psychopathology profile. The most common areas of clinically elevated levels of impairment in WS included Attention Problems, Affective Problems, Anxiety Problems and Attention Deficit/Hyperactivity Problems. Low rates of behaviour impairment/psychopathology were found for TD controls. While chronological age was not significantly related to behaviour impairments or psychopathological symptoms in WS children, there were significant, negative relationships between chronological age and some behaviour /psychopathology ratings in TD controls. There were no significant relationships between CBCL ratings and verbal, nonverbal or global ability in either WS preschool children or TD controls. Finally, Study 5 utilised the Differential Ability Scales – Second Edition (DAS-II) and found variability in cognitive skills amongst both WS children (N=22, aged 3.98 to 7.70 years) and CA age-matched TD controls, although scores in the TD sample remained in the normal or unimpaired range. Study 5 revealed that 50% of the WS children displayed a significant and abnormal weakness in spatial skills relative to verbal skills.

The findings of this thesis suggest individual variability, as well as some common areas of strength/impairment across various cognitive abilities, psychopathology/behaviour problems and everyday executive functions in WS and DS. The clinical implications of these results are discussed, as well as directions for future research.