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.