DISCUSSION
The findings in exome sequencing of two multiplex families with severe
stuttering are discussed. Considering the previously implicated genes
(GNPTAB , GNPTG , NAGPA and AP4E1 ) only one
pathogenic heterozygous missense variant (c.322G>A;
p.Glu108Lys) in NAGPA was detected in our study. Since the so far
implicated genes in stuttering are limited to a single lysosomal
pathway, we extended the analyses to the 123 genes also, known in
lysosomal function, but did not identify any significant variation in
them in our two families.