# Reduced Respiratory Sinus Arrhythmia in Infants with the FMR1 Premutation

## TL;DR

Infants with the FMR1 gene premutation show reduced respiratory sinus arrhythmia, indicating early autonomic nervous system differences.

## Contribution

This study identifies RSA as a potential ANS biomarker in infants with the FMR1 premutation.

## Key findings

- FXpm infants had significantly lower RSA compared to neurotypical infants.
- No significant differences were found in interbeat interval (IBI) between FXpm and neurotypical infants.
- ANS functioning was not associated with CGG repeat length in FXpm infants.

## Abstract

The fragile X premutation (FXpm) is caused by a CGG repeat expansion on the FMR1 gene. In adults, FXpm is linked with autonomic nervous system (ANS) dysfunction and impairment is associated with CGG repeat length. Given scant infancy research, we examined ANS functioning, via respiratory sinus arrhythmia (RSA) and interbeat interval (IBI), in 82 FXpm and neurotypical infants and their associations with CGG repeats. FXpm infants exhibited lower RSA but no IBI differences. There were no associations between ANS functioning and CGG repeat length. These findings identify an ANS biomarker consistent with the emerging pediatric phenotype in FXpm.