Fragile X syndrome (FXS) is a genetic disorder caused by a trinucleotide (CGG) expansion mutation in the Fmr1 gene located on the X chromosome. It is characterized by hyperactivity, increased anxiety, repetitive-stereotyped behaviors, and impaired language development. Many children diagnosed with FXS also experience seizures during their lifetime. However, the underlying etiology of the relationship between FXS and epilepsy is not fully understood. Ultrasonic vocalizations (UVs) are one tool that may be used to measure early behavioral changes in mouse pups. In the present study, neonatal UVs were analyzed as a measure of communicative behavior in a mouse model of FXS, both with and without early-life seizures (ELSs). On postnatal day (PD) 10, status epilepticus (SE) was induced via intraperitoneal injections of 0.5% kainic acid (2.0 mg/kg) in male Fmr1 knockout (KO) and wild-type (WT) mice. On PD 12, all pups were temporarily isolated from their dam and UVs were recorded. Significant alterations were found in both spectral and temporal measures across genotype and seizure groups. Early-life seizure experience resulted in a significant increase in the quantity of UVs only in WT animals (p < 0.05). We also found that while there was no difference between genotypes in the total number of vocalizations made, calls produced by Fmr1 KO mice were significantly shorter and had a higher peak frequency compared with WT mice. Overall, these findings support the use of vocalization behavior as an early phenotypic marker and highlight the importance of utilizing double-hit models to better understand comorbid disorders.
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