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Autonomic Nervous System Function and Sensory Sensitivity in 12-Month-Old Infants with the FMR1 Premutation

Amelia Morton1, Holley Arnold2,3, Lisa Hamrick2,3

  • 1Floyd School of Medicine, University of South Carolina, Columbia, SC 29209, USA.

International Journal of Molecular Sciences
|August 13, 2026
PubMed

Insights

Fragile X premutation (FXpm) infants show no significant differences in sensory responsiveness at 12 months. However, longer CGG repeat lengths in FXpm were linked to fewer hyperresponsive behaviors, suggesting early biological variability.

Area of Science:

  • Neuroscience
  • Genetics
  • Developmental Psychology

Background:

  • Fragile X premutation (FXpm) involves expanded CGG repeats in the FMR1 gene.
  • FXpm is linked to sensory processing and autonomic regulation challenges in children and infants.
  • The relationship between autonomic nervous system (ANS) function, molecular variables, and sensory responsiveness in infancy remains understudied.

Purpose of the Study:

  • To investigate parent-reported sensory responsiveness in 12-month-old infants with FXpm compared to neurotypical (NT) controls.
  • To examine associations between sensory responsiveness and autonomic measures (respiratory sinus arrhythmia [RSA], interbeat interval [IBI]) in infancy.
  • To explore the relationship between CGG repeat length and sensory responsiveness in infants with FXpm.

Main Methods:

  • Recruited 12-month-old infants: 35 with FXpm and 55 NT controls.
  • Assessed parent-reported sensory responsiveness.
  • Measured baseline RSA and IBI as indicators of ANS functioning.
  • Recorded CGG repeat length in the FMR1 gene for the FXpm group.

Main Results:

  • No significant differences in hyporesponsive or hyperresponsive sensory behaviors were found between FXpm and NT infants.
  • No significant associations were observed between baseline RSA or IBI and sensory responsiveness in either group.
  • Within the FXpm group, a longer CGG repeat length correlated with lower scores for hyperresponsive sensory behaviors.

Conclusions:

  • Behavioral manifestations of sensory processing differences may not be apparent in infants with FXpm at 12 months.
  • Biological variability, indicated by CGG repeat length, shows an early association with sensory responsiveness in FXpm.
  • Further research is needed to understand genetic and physiological factors influencing later behavioral phenotypes in early FXpm development.

Keywords:
CGG repeat lengthFMR1 premutationautonomic nervous systemhyperresponsivehyporesponsiveinterbeat intervalrespiratory sinus arrhythmia

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