Lack of Williams syndrome-associated genes alters quantity discrimination in zebrafish

The ability to discriminate sets of items based on their numerosity is alleged to be an evolutionary conserved mechanism in all vertebrates. People with Williams syndrome (WS), a rare multigenic condition, show altered number and quantity cognition abilities. Assessing the contribution of specific genes to WS using animal models could help understand the basis of numerical impairments. Here, we assessed the quantitative abilities of juvenile zebrafish (Danio rerio) with loss of function of two of the genes affected in WS using a group size preference behavioural assay. The selected genes were: baz1b, implicated in neural crest development; and fzd9b, associated with neuronal functioning. The contrasts studied were 2 versus 5, 2 versus 4 and 2 versus 3. While group-level comparisons did not reveal statistically significant genotype differences, single-sample tests suggested a reduced preference for larger shoals in some contrasts among mutants. These trends were more apparent when the total number of items likely exceeded working memory capacity (i.e., 6 or more items), while performance on small numerosity contrasts remained relatively intact. These data agree with previous analyses of humans with WS and offer preliminary evidence that specific genes may influence quantity discrimination. Our research also supports the use of zebrafish as model organisms in which to characterise the neurobiological basis of dyscalculia in WS and associated disorders.