Possible genetic factors in cluttering: Dennis Drayna
First, the basic epidemiology of cluttering is not currently well understood. This has partly been due to diﬀerences in the precise clinical criteria used for diagnosis of the disorder. A broadly applicable and widely accepted set of diagnostic criteria will enable estimates of the incidence and prevalence of cluttering (see St. Louis & Schulte, chapter 14 this volume; Ward, chapter 15 this volume). They will also allow estimates of familial recurrence rates, which often provide the ﬁrst hints of a genetic etiology for a disorder. Another hurdle in our understanding of cluttering epidemiology is the fact that cluttering can co-occur with other speech disorders (see Scaler Scott, chapter 8 this volume; Van Borsel, chapter 6 this volume; Van Zaalen, Wijnen, & Dejonckere, chapter 7 this volume), which injects additional com plexity into this task. Clear diﬀerentiation of syndromic and non-syndromic presentations of cluttering will be an important starting point for a better understanding of the distribution of this disorder. At this time, what can be said is that cluttering does not appear to be an especially common disorder, and is probably less frequent than stuttering (but see also its heightened occurrence in a small sample of children with Asperger’s disorder in Scaler Scott, chapter 8 this volume).