Dennis Drayna

Abstract: Background: Previous studies identified a strong linkage signal for non-syndromic persistent developmental stuttering on chromosome 3q13.2-3q13.33 in a large consanguineous family of Pakistani origin. To identify the causative genetic variant at this locus, we performed further analysis, including whole exome, whole genome, and targeting Sanger sequencing. Results: We identified a homozygous rare c.2155G>A variant in ZBTB20 in individuals who stutter. This mutation encodes Isoleucine in place of a highly conserved Valine at amino acid position 719 in ZBTB20 that co-segregates (LOD = 4.23) with stuttering under a model of recessive inheritance with reduced penetrance in this family. Coding variants in this gene were significantly more frequent in a multiethnic cohort of unrelated individuals who stutter than in individuals in large population databases comprised of our normal control subjects and gnomAD database subjects matched for ethnicity. ZBTB20 encodes a zinc-finger transcription factor, and luciferase reporter constructs using genes known to be regulated by ZBTB20 showed that the Ile719 mutant form of the protein displays altered transcriptional regulation in vitro. Although homozygosity for mutations in ZBTB20 has not previously been observed, dominant mutations in ZBTB20 have been reported in Primrose syndrome, a rare Mendelian dominant disorder characterized by tall stature, developmental delay, dysgenesis of the corpus callosum, but generally not speech disorders. Clinical re-examination of the affected family members ten years after their original ascertainment revealed only some suggestive signs associated with Primrose syndrome. Conclusions: Our findings support variants in ZBTB20 as a cause of stuttering in a large family, and rarely in the wider population. Previous studies in mice have demonstrated that Zbtb20 is required for the development of astrocytes, a brain cell type previously implicated in an animal model of stuttering. Our findings support our hypothesis that astrocyte pathology is involved in this disorder. Our findings also broaden the medical genetic view of disorders of ZBTB20, and demonstrate that individuals carrying a homozygous mutation in this gene can be viable, and that they can primarily display persistent developmental stuttering.