RESUMEN
This study examined the association between two common polymorphisms, the dopamine D4 receptor (DRD4) gene and the serotonin transporter promoter (5-HTTLPR) gene and temperament in 61 infants aged 12 months. Twenty-two infants had a least one copy of the 6-8 repeat DRD4 alleles (L-DRD4) and 39 had two copies of the 2-5 repeat allele (S-DRD4). Twenty infants were homozygous for the short form (s/s) of 5-HTTLPR while 41 were either heterozygous for the short and the long form (l/s) or were homozygous for the long form (l/l). The infants were observed in a series of standard temperament episodes that elicited fear, anger, pleasure, interest, and activity. L-DRD4 infants showed less interest in a structured block play situation and more activity in a free play situation. They also displayed less anger in an episode of mild physical restraint. Infants with s/s 5-HTTLPR showed less fearful distress to stranger approach and less pleasure in a structured play situation than infants with l/l or l/s 5-HTTLPR. Duration of looking during block play was affected by a significant interaction between DRD4 and 5-HTTLPR. Shortest duration of looking was associated with the L-DRD4 and s/s 5-HTTLPR genotypes. The implications and limitations of these findings are discussed.
Asunto(s)
Proteínas Portadoras/genética , Conducta del Lactante , Glicoproteínas de Membrana/genética , Proteínas de Transporte de Membrana , Proteínas del Tejido Nervioso , Receptores de Dopamina D2/genética , Serotonina/metabolismo , Temperamento , Ira , Miedo , Femenino , Humanos , Lactante , Masculino , Polimorfismo Genético , Regiones Promotoras Genéticas , Receptores de Dopamina D4 , Muestreo , Proteínas de Transporte de Serotonina en la Membrana PlasmáticaRESUMEN
The dopamine D4 receptor (DRD4) exon III polymorphism has generated interest because of its association with attention deficit hyperactivity disorder (ADHD), with an increased frequency of the seven-repeat allele being reported in children with ADHD. Deficits in sustained attention and information processing characterize ADHD, and individual differences in these functions are apparent from infancy. We found that in a structured play situation and on an information-processing task, 1-year-old infants with the 7-DRD4 allele showed less sustained attention and novelty preference than do infants without the 7-DRD4 allele. There was also a significant interaction between DRD4 and the serotonin transporter promoter (5-HTTLPR) gene on a measure of sustained attention. Our results provide evidence for a possible developmental link between DRD4 and ADHD via early sustained attention and information processing. It also points to the importance of considering the influence of more than one gene in studies of behavior.