A DNAzyme based knockdown model for Fragile-X syndrome in zebrafish reveals a critical window for therapeutic intervention

INTRODUCTION

FXS is the leading cause of intellectual disabilities in males and a major monogenic cause of ASD (Autism spectrum disorders). It occurs due to the loss of FMRP, whose role in early development is not well understood. In this study, we have used a novel DNAzyme based approach to create a larval model of FXS in zebrafish with specific focus on the early developmental window.

METHODS

Fmr1specific DNAzymes were electroporated into embryos to create the knockdown. Changes in RNA and protein levels of FMRP and relevant biomarkers were measured in the 0-7dpf window. Behavioral tests to measure anxiety, cognitive impairments and irritability in the larvae were conducted at the 7dpf stage. Drug treatment was carried out at various time points in the 0-7dpf window to identify the critical window for pharmacological intervention.

RESULTS

The DNAzyme based knockdown approach led to a significant knockdown of FMRP in the zebrafish embryos, accompanied by increased anxiety, irritability and cognitive impairments at 7dpf, thus creating a robust larval model of FXS. Treatment with the Mavoglurant was able to rescue the behavioral phenotypes in the FXS larvae, and found to be more efficacious in the 0-3dpf window.

DISCUSSION

The results from this study have revealed that a) a DNAzyme based knockdown approach can be used to create robust larval zebrafish model of disease, in a high-throughput manner and b) optimal window for therapeutic intervention for FXS as well as other pediatric diseases with a monogenic cause can be identified using such a model.

Detailed assessment of incontinence in boys with fragile-X-syndrome in a home setting

Fragile-X-syndrome (FXS) is caused by a mutation on the X chromosome (Xq27.3). Males with a full mutation have typical dysmorphic signs, moderate intellectual disability and psychological disorders. Twenty-five to fifty percent are affected by incontinence. The aim of the study was to assess subtypes of incontinence and psychological problems in children with FXS in their home environments. Twenty-two boys with FXS (mean age 11.0 years) and 22 healthy controls (mean age 11.1 years) were examined with sonography, uroflowmetry, 48-h bladder diary, physical examination, IQ test, parental psychiatric interview and questionnaires regarding incontinence and psychological symptoms in a home setting. Boys with FXS had higher rates of incontinence than controls (59.1 vs. 4.8 %). The most common subtypes in FXS boys were primary non-monosymptomatic nocturnal enuresis, urge incontinence and nonretentive faecal incontinence. 90.9 % boys with FXS had a psychological comorbidity. Incontinence and behavioural symptoms were not associated.

CONCLUSION

Boys with FXS have a higher risk for physical disabilities, psychological disorders and incontinence than healthy boys. Constipation is not a major problem in FXS. As effective treatment is available for children with ID, we recommend offering assessment and therapy to all children with FXS and incontinence.

WHAT IS KNOWN

• Boys with fragile-X-syndrome (FXS) have higher rates of incontinence, psychological disorders and somatic conditions than typically developing boys. What is New: • Constipation is a rare condition in FXS in contrast to other genetic syndromes. • Although incontinence rates are higher, urological findings (uroflowmetry, sonography) are not more pathological per se in FXS.