Variación de alelos del gen receptor de dopamina DRD4 en escolares chilenos de diferente origen étnico y su relación con riesgo de déficit atencional/hiperactividad / DRD4 dopamine receptor alleles in Chilean students of different ethnic origin and its relation with the risk for attention deficit/hyperactivity disorder

Background: Worldwide diversity of alleles of D4 receptor gene (DRD4), linked to attention deficit hyperactivity disorder (ADHD), is mostly the result of length and single nucleotide polymorphisms in a 48-bp tandem repeat (VNTR). Alleles containing from two (2R) to eleven (11R) repeats have been identified. The most common are 4R, 7R and 2R. Aim: To study the association of ADHD risk with DRD4 genotypes in Chilean students. Subjects and Methods: ADHD risk data were obtained through the abbreviated Conner's Scale for School Teachers in 66 Aymara children (11 cases and 55 controls), 91 Rapa-Nui children (60 cases ad 31 controls) and 96 children from a mixed urban population from Santiago (51 cases and 45 controls). DNA extracted from saliva was amplified by polymerase chain reaction (PCR) to genotype the DRD4 VNTR. Results: The distribution of DRD4 alleles reveals that, beneath the 4R allele, 7R exhibits the second highest frequencies in Aymara and Santiago children. In Polynesian children, 2R ranks after 4R. A statistically significant association between ADHD risk and 2R/4R genotype was identified in Polynesian children (p < 0.05; odds ratio = 3.7). Conclusions: Different DRD4 genotypes are associated with ADHDphenotype in Chilean populations, probably as a consequence of their initial colonization history.

Riesgo de déficit atencional/hiperactividad en escolares Aymara, Rapa-Nui y de Santiago de Chile: Posible contribución de polimorfismos genéticos del sistema dopaminérgico / Risk of attention deficit/hyperactivity disorder in Aymara and Rapa-Nui school children: Association with dopaminergic system polymorphisms

Background: Attention deficit/hyperactivity disorder (ADHD) is a common, highly heritable neurobiological disorder of childhood onset, characterized by hyperactivity, impulsiveness or inattentiveness. Aim: To search for differences in risk for ADHD and its components among Chilean native and mixed populations and to look forpossible associations with dopamine receptor D4 (DRD4) and dopamine transporter 1 (DAT1) polymorphisms. Material and Methods: School teachers were requested to complete the Conners test, which uses DSM-IV criteria, to screen for ADHD risk among Aymara and Rapa-Nui students. Results: Rapa-Nui children from Easter Island had the highest risk of hyperactivity/impulsiveness. Aymara children from the Arica-Parinacota Region had lower scores. Although inattentiveness scores had lower differences between groups, overall ADHD score differences among studied populations were highly significant. DRD4 and DAT1 alleles had a heterogeneous distribution. Easter islanders had more divergent frequencies, mostprobably as a result of separate migration routes utilized at different timeperiods during the colonization of America and Polynesia. Conclusions: The comparison of ADHD risk parameters between Rapa-Nui and Aymara children showed marked differences. Allele distri-bution of dopamine polymorphisms in Easter Island was also significantly different from northern Chile, due probably to different colonization histories. These findings suggest that higher ADHD risk scores in Easter Island children may be linked to the presence of different DRD4 alleles.