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TDK conference 2008

Observed temperament characteristics in infancy
Varga Zsófia - year 5
Institute of Biology, Department of Ecology
Supervisors: Dr. Gervai Judit, Dr. Kabai Péter


Newborn babies’ behavioural responses to environmental cues are highly variable. This suggests that temperament characteristics have a biological basis. Behaviour depends on the neurotransmission in the central nervous system, and signalling depends on the structure of the receptors. Receptor structures vary with the corresponding polymorphisms of the coding DNA sequences. I have studied the relationships between early temperament characteristics and the common gene polymorphismsof the dopamine D4 and the μ-opioid receptors in 16-month-old infants. Dopamine controls emotions, movements and the rewarding system of the brain. One important role of the opioid system is to modulate social attachments. In the coding region of the dopamine D4 receptor (DRD4) gene, a 48 bp sequence is repeated 2-10 times. This polymorphism is linked to novelty-seeking in adults. At the 118 position of the μ-opioid receptor gene, an adenine was replaced by guanine, which increases ligand affinity. Previous studies found association between this polymorphism and stress reaction in social separation.

Infant temperament was observed in the Strange Situation Test (SST, Ainsworth). SST consists of 8 episodes measuring the balance between attachment and exploration. It can also be used for measuring temperament. The 2nd and 3rd episodes are suitable for studying the infant's reactions to a novel object and a novel social environment. The 4th, 6th and 7th episodes are suitable for investigating the infant's distress while separated from its caregiver.

Infants with the 7-repeat DRD4 allele responded with less anxiety to novel objects. This genotype effect was stronger for boys than for girls. Infants with the AA genotype in μ-opioid receptor gene were more distressed than infants with the AG genotype. However, this relationship was found in only two of the three episodes involving separation from the caregiver. Data for the same 12-month-old babies were also available, so I compared behaviour in the two ages. Infants were tested with their mothers and with their fathers at at 12 and 16 months of age, respectively. Thus, potential age effects could not be separated from the effect of the presence of different parents at the two ages. Infants in the two tests differed in crying latency, in negativity and in anxiety during separation.

In this study I found association between dopamine D4 and μ-opioid receptor gene polymorphisms and temperament characteristics. My results are consistent with some of the previous studies. To the best of my knowledge, this study provides the first evidence that the D4 gene affects the two sexes differently.

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