Sex-specific and genotype-specific differences in vocalization development in FMR1 knockout mice.

Fragile X syndrome is a neurodevelopmental disorder caused by a trinucleotide (CGG) hyperexpansion in the FMR1 gene, functionally silencing transcription of the fragile X mental retardation protein (FMRP). This disorder is characterized by impaired cognition, communication, and social behavior. The aim of this study was to investigate the development of ultrasonic vocalization (USV) behavior in a Fmr1-deficient mouse model. On postnatal days (PD) 9-14, separate cohorts of FVB/NJ pups were removed from their homecage and isolation-induced USVs were recorded. There were significant genotype-dependent and sex-dependent differences in USV behavior across the different testing days. Fmr1 knockout (KO) mice showed a significant reduction in vocalizations across all days. There was also a significant difference in vocalizations between male and female mice. We found a significant decrease in the total number of calls for KO males on PD9 and PD13 as well as an increase in the total number of calls for KO males on PD12. The KO males also showed a significant increase in the total call duration on PD12 and a reduction on PD13. The KO female showed a significant decrease in the total number of calls on PD9 and PD10. They also showed a significant decrease in the total call duration on PD9 and a marginal decrease in the total call duration on PD10. These results provide additional evidence for communication deficits in Fmr1 deficient mice and provide new insight suggesting sexually dimorphic vocalizations during the neonatal period.