GENETICS OF STUTTERING

Abstract

Stuttering is characterized by frequent repetition or lengthening of sounds, syllables or words, or by frequent hesitations or pauses that disrupt the rhythmic flow of speech. It may be accompanied by movements of the face and/or other parts of the body that coincide in time with the repetitions, prolongations, or pauses in speech flow. The prevalence of stuttering ranges from 0.3% to 5.6%. Usually for 80%-90% of patients stuttering starts gradually when children are 2-7 years old. Longitudinal research shows that 65% -85% of stuttering children recover. The rate of heritability of stuttering is about 70%, indicating that almost one third of the disorder is caused by environmental factors. Currently four stuttering genes have been identified that are involved in intracellular metabolism: GNPTAB, GNPTG, NAGPA and AP4E1. The disorder is caused by single nucleotide synonymous or missense mutations in the exons of these genes. Different people affected by stuttering can carry different sets of mutant variants ‒ from one to several. The effect of the identified genes on neurobiological processes in the human brain and on the development of stuttering remains unknown. So far it has only been discovered that stuttering occurs due to lysosomal dysfunction, which adversely affects the organization of neurofilaments of speech neural networks. The contribution of identified genes to stuttering cumulatively is only 20%. There were identified also 9 candidate stuttering genes (FADS2, PLXNA4, CTNNA3, ARNT2, EYA2, PCSK5, SLC24A3, FMN1 and ADARB2) and 7 regions of 6 chromosomes (2p, 3p, 3q, 12q, 14q, 15q and 16q) reliably linked to this disorder.
 Further successful genetic studies of stuttering are needed to improve our understanding and treatment of this long-enigmatic disorder.