Unit 2 – Incidence, Prevalence, & Variability; familial prevalence, twins, adoption, genes, other populations, ethnoculture, study findings

Genetic perspective; concordance rate in twins

Higher concordance rate in identical twins than fraternal twins AND in fraternal twins than that of ordinary siblings

Genetic perspective; concordance rate in twins; discordant

If only one member of a twin pair has a condition and the other does not, then the pair is described as

Genetic perspective; concordance rate in twins; Supports the hypothesis that stuttering is

inherited

Genetic perspective; Genes

Genetic linkage studies (Drayna); Comparing DNA among family members/Numerous studies have been published

Genetic perspective; Genes; Genome-Wide Association Study (Kraft, 2010)

More interested in genes, not chromosomes/Identified 10 "candidate genes"/Subdivided into neural development, neural function, and behavior

Genetic perspective; Genotyping

There is strong evidence for major genetic components to stuttering/Studies analyzing DNA materials to locate candidate genes have been promising

A somewhat higher prevalence of stuttering than for the general population has been reported for

Individuals with cognitive impairment

Prevalence of stuttering in individuals with cognitive impairment examples

Early studies 14-17% (Gottsleben, 1995; Schlanger & Gottsleben, 1957)/Later studies 2.5% to 7 % (Chapman & Cooper, 1973; Schaeffer & Shearer, 1968/Down Syndrome in particular - 15% (Schubert, 1966) up to 53.2% (Preus, 1973)/Suresh et al (2006) found the strongest indications for genes underlying stuttering on chromosome

A lower prevalence of stuttering has been reported in

deaf and hard of hearing individuals

Stuttering in deaf persons with oral skills has been documented but with very low prevalence rates

(.05% Backus, 1938; Harms & Malone, 1939)

A lower prevalence of stuttering has been reported in the

cleft palate population (Dalston 1987, .2%)

Some experts, Johnson, have claimed that stuttering is

a culturally determined disorder/ This is in line with the diagnsogenic theory of stuttering

Johnson believed that

societies/cultures that place heavy emphasis on verbal skills have higher prevalence of stuttering/Native Americans do not stutter; Snidecore, 1947 claimed Native Americans didn't have word for stuttering/INACCURATE

Johnson's theory has been

contradicted by data - stuttering is found in almost all societies and ethnocultural groups; The prevalence rates may be somewhat different in different ethnocultural groups

West, Nelson, and Berry (1939)

100/204 participants reported no family history of stuttering; 85/100 participants reported congenital or early childhood factors; Conclusion was congenital or early childhood factors may be a predisposition for stuttering

Poulos & Webster (1991)

57/169 participants reported no family history of Stuttering; 37% reported congenital or early childhood factors; Conclusion was congenital or early childhood factors may be a predisposition for stuttering

Alm & Risberg (2007)

23/32 (72%) reported a family history of stuttering; 17/32 (53%) sustained neurological lesions prior to the onset of stuttering; 7/9 (78%) with no family history of stuttering, reported pre-onset neurological lesions; Supports hypothesis that 2 different predispositions may contribute to stuttering; Genetic inheritance/Brain injury