Abstract
OBJECTIVE: To examine the impact of polymorphic variation in the solute carrier family 5 member 7 (SLC5A7) gene on autonomic nervous system (ANS) reactivity indexed by respiratory sinus arrhythmia (RSA) and heart rate (HR) in infants during a dyadic stressor, as well as maternal report of infant self-regulation. Given evidence of race differences in older individuals, race was specifically examined. METHODS: RSA and HR were collected from 111 infants during the still-face paradigm (SFP). Mothers completed the Infant Behavior Questionnaire-Revised short-form. Multi-level mixed effects models examined the impact of SLC5A7 genotype on RSA and HR across the SFP. Linear models tested the influence of genotype on the relation between RSA, HR, and maternal report of infant self-regulation. RESULTS: SLC5A7 genotype significantly predicted RSA stress responsivity (β = -0.023; p = 0.028) and HR stress responsivity (β = 0.004; p = 0.002). T-allele carriers exhibited RSA suppression and HR acceleration in response to stress while G/G homozygotes did not suppress RSA and exhibited less HR acceleration. All infants exhibited modest RSA augmentation and HR deceleration during recovery. Race-stratified analyses revealed that White T-allele carriers drove the overall results for both RSA (β = -0.044; p = 0.007) and HR (β = 0.006; p = 0.008) with no relation between SLC5A7 genotype and RSA or HR in Black infants. Maternal report of infant orienting/regulation was predicted by the interaction of SLC5A7 genotype and both RSA recovery (β = 0.359; p = 0.001) and HR recovery (β = -1.659; p = 0.020). RSA augmentation and HR deceleration during recovery were associated with higher maternal reports of self-regulation among T-allele carriers, a finding again primarily driven by White infants. CONCLUSIONS: Early in development, genetic contributions to ANS are evident and predict maternal report of infant self-regulation within White infants, consistent with prior literature. The lack of associations in Black infants suggest that race differences in physiological reactivity and self-regulation are emerging during the first year of life potentially providing early evidence of disparities in health risk trajectories.