Genetic studies in developmental stuttering are important for their potential in ultimately determining pathophysiological basis of this disorder. This study will combine two approaches to examine genetic aspects of stuttering, linkage in families, and candidate gene analysis. Linkage studies will be completed using adult individuals who are diagnosed as persons who stutter and those who can be judged as never having stuttered from one or more families with large numbers of affected individuals within several generations. Candidate gene analyses will also be carried out in adults who stutter to determine if the frequency of polymorphisms for certain neurotransmitter receptors and enzymes differ from control populations. In addition, given the heterogeneity of the population of adults who stutter, other phenotypic probes such as motor skills, language skills, neuropsychological abilities and psychological responses to stuttering will also be assessed in order to identify subgroups in which the phenotype expression of the gene may differ.