A role for inherited metabolic deficits in persistent developmental stuttering

Area of Science:

• Genetics and Molecular Biology
• Neuroscience
• Speech and Language Pathology

Background:

• Stuttering is a prevalent speech disorder with a significant, yet poorly understood, genetic component.
• Identifying causative genetic variants is crucial for understanding the molecular and cellular mechanisms underlying stuttering.

Purpose of the Study:

• To review gene discoveries associated with stuttering to date.
• To summarize functional studies investigating how identified gene mutations may lead to stuttering.

Main Methods:

• Literature review of genetic association studies in stuttering.
• Analysis of functional studies on identified genes and their encoded enzymes.
• Comparison of mutation types in stuttering versus related lysosomal storage disorders.

Main Results:

• The first identified stuttering-associated genes (GNPTAB, GNPTG, NAGPA) are involved in the lysosomal targeting system.
• Mutations in GNPTAB and GNPTG are also linked to mucolipidosis, a lysosomal storage disorder.
• Stuttering-associated mutations are predominantly missense, unlike the truncating mutations seen in mucolipidosis.
• Biochemical studies show NAGPA mutations in stuttering reduce enzyme activity by approximately 50% and impair protein processing and trafficking.

Conclusions:

• Genetic evidence strongly implicates lysosomal targeting pathways in stuttering.
• Mutations in genes like NAGPA affect enzyme function and cellular protein handling, potentially contributing to speech pathology.
• Further research, including studies in animal models, is needed to elucidate the precise link between these genetic deficits and stuttering neuropathology.