Background: Williams (SW) and Down (DS) syndromes are associated with cognitive impairment and emotional and behavioural problems, that vary in topographies and severity. The Child Behavior Checklist for Ages 6-18 (CBCL/6-18) has critical items from the empirically based syndrome scales and DSM-oriented scales, which refer to severe emotional and behavioural difficulties. These items may raise challenges for management. This study investigated severe behavioural and emotional problems in Brazilian children and adolescents with WS and DS using CBCL critical items.

Methods: 96 parents of children with WS and DS participated (41 with DS, 60% boys, mean age=12.3 y/o (minimum 6, maximum 17), SD=2.59 and 55 with WS, 52% boys, mean age of 11.2 y/o (minimum 6, maximum 18), SD=4.19; age did not differ significantly between groups). CBCL critical items are scored as 0 (Not true), 1 (somewhat or sometimes true) or 2 (very true or often true).

Results: All parents from both syndromes endorsed 1 or 2 in at least one critical item. The items “Sees things that aren’t there” (p=0.002; Z=-3.13; Effect size=-0.319), “Physically attacks people” (p=0.002; Z=-3, 15; Effect size=-0.321), “Deliberately harms self or attempts suicide” (p=0.049; Z=-1.97; Effect size=-0.201), and “Wets Self during the day” (p=0.004; Z = -2.89; Effect size=-0.294) had higher scores for the WS group. The only item in which the group with DS showed worse indicators was “Sets fire” (p=0.023, Z=-2.27; effect size: 0.231).

Conclusion: Both syndromes had indicators of severe emotional and behavioural problems that require special mental health attention. Individuals with WS in the sample had higher scores, indicating a more worrying profile. In addition to the fundamental need for individualized assessments and interventions, Brazilian individuals must receive more mental health services, especially in the elaboration of public policies since there are no official guidelines for rare syndromes like WS in Brazil.

Keywords: CBCL/6-18, critical items, Down syndrome, Williams syndrome, emotional and behavioural problems