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Background The association of behavioural phenotype assessment with cytogenomic characterisation may provide a better comprehension of genotype–phenotype correlations in syndromes caused by chromosomal abnormalities, such as 18p deletion syndrome. Method We report on four Brazilian patients with 18p deletion syndrome characterised by cytogenomic techniques and detailed neuropsychological evaluation. Intellectual, adaptive and behavioural characteristics were assessed through the Wechsler's Scales, the Vineland‐II Scale and the Child Behaviour Checklist, respectively. Socio‐economic measures including main caretaker educational level and family income as defined by Brazilian criteria for social class classification were also collected to evaluate a possible contribution of environmental factors in neurocognitive variability. Results Two out of four patients showed intellectual disability (IQ < 70). Wechsler's scale results suggest that in our sample, interpretation of social situations based on observation of non‐verbal behaviour constitute a cognitive strength while judgement of social rules and language skills associated with word knowledge and verbal fluency may be a cognitive weakness. Concerning adaptive behaviour, motor and socialisation domains showed to better develop than communication and daily living skills on the Vineland‐II Scale. Only one patient presented internalising behavioural problems based on the Child Behaviour Checklist. Our results also suggested that socio‐economic status may contribute to overall patient development. Conclusion Our results suggest that some 18p deletion syndrome patients may present average intellectual performance and that the segment deletion size and some families' socio‐economic conditions may influence cognitive development.

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The 22q11.2 Deletion Syndrome (22q11.2DS), the most common human chromosome microdeletion syndrome, is associated with a very heterogeneous neurocognitive phenotype. One of the main characteristics of the syndrome spectrum is the intellectual variability, which encompasses average performance and intellectual disability and discrepancies between Verbal Intelligence Quotient and Performance Verbal Intelligence Quotient, with greater impairment in nonverbal tasks. The present study aimed at investigating the intellectual performance aspects of a 21children and adolescents sample from Brazil who had been diagnosed with 22q11.2DS, based on the Wechsler Intelligence Scale for Children - 4th edition. The samples were reviewed considering the differences between indices. The results revealed an Full Scale Intelligence Quotient predominant in the borderline range (42 to 104) and a significant discrepancy between the indices of Verbal Comprehension and Perceptual Reasoning in 42% of the sample. With regard to the performance in the subtests alone, a better performance was found in Similarities, whereas block design, matrix reasoning, digit span and letter-number sequencing subtests were the most challenging. These findings indicate that a comprehensive assessment of intellectual performance aspects covering the different measures of the Wechsler Intelligence Scale may contribute to a broader understanding of the neurocognitive phenotype associated with 22q11.2DS.