Genomic imprinting and the expression of affect in Angelman syndrome: what's in the smile?

BACKGROUND: Kinship theory (or the genomic conflict hypothesis) proposes that the phenotypic effects of genomic imprinting arise from conflict between paternally and maternally inherited alleles. A prediction arising for social behaviour from this theory is that imbalance in this conflict resulting from a deletion of a maternally imprinted gene, as in Angelman syndrome (AS), will result in a behavioural phenotype that should evidence behaviours that increase access to maternally provided social resources (adult contact). METHOD: Observation of the social behaviour of children with AS (n = 13), caused by a deletion at 15q11-q13, and a matched comparison group (n = 10) was undertaken for four hours in a socially competitive setting and the effect of adult attention on child behaviours and the effect of child smiling on adult behaviours evaluated using group comparisons and observational lag sequential analyses. RESULTS: The AS group smiled more than the comparison group in all settings, which had different levels of adult attention, and more when the level of adult attention was high. Smiling by children with AS evoked higher levels of adult attention, eye contact and smiling both than by chance and in comparison to other children and this effect was sustained for 30 s to 50 s. Smiling by children with AS was frequently preceded by child initiated contact toward the adult. DISCUSSION: The results are consistent with a kinship theory explanation of the function of heightened levels of sociability and smiling in Angelman syndrome and provide support for an emotion signalling interpretation of the mechanism by which smiling accesses social resources. Further research on other behaviours characteristic of Angelman and Prader-Willi syndromes warrant examination from this perspective.