Editing Stuttering (section)

==Causes==
The cause of developmental stuttering is complex. It is thought to be neurological with a genetic factor.<ref name=":4">{{Cite book|title=A handbook on stuttering|last1=Bloodstein|first1=Oliver|last2=Ratner|first2=Nan Bernstein|publisher=Cengage Learning|year=2007|isbn=978-1-4180-4203-5|page=142}}</ref><ref>{{Cite web|date=2019-08-16|title=NIH study in mice identifies type of brain cell involved in stuttering|url=https://www.nidcd.nih.gov/news/2019/nih-study-mice-identifies-type-brain-cell-involved-stuttering|access-date=2021-05-16|website=NIDCD|language=en}}</ref>

Various hypotheses suggest multiple factors contributing to stuttering. There is strong evidence that stuttering has a genetic basis.<ref name="Guitar5–6">{{harvnb|Guitar|2005|pp= 5–6}}</ref> Children who have [[first-degree relative]]s who stutter are three times as likely to develop a stutter.<ref>{{harvnb|Ward|2006|p= 11}}</ref> In a 2010 article, three genes were found by [[Dennis Drayna]] and team to correlate with stuttering: [[GNPTAB]], [[GNPTG]], and [[NAGPA]]. Researchers estimated that alterations in these three genes were present in 9% of those who have a family history of stuttering.<ref>{{cite journal |last1=Kang |first1=Changsoo |last2=Riazuddin |first2=Sheikh |last3=Mundorff |first3=Jennifer |last4=Krasnewich |first4=Donna |last5=Friedman |first5=Penelope |last6=Mullikin |first6=James C. |last7=Drayna |first7=Dennis |title=Mutations in the Lysosomal Enzyme–Targeting Pathway and Persistent Stuttering |journal=New England Journal of Medicine |date=25 February 2010 |volume=362 |issue=8 |pages=677–685 |doi=10.1056/NEJMoa0902630 |pmid=20147709 |pmc=2936507 }}</ref><ref>{{cite web |url=http://children.webmd.com/news/20100210/genetic-mutations-linked-to-stuttering |title=Genetic Mutations Linked to Stuttering |publisher=Children.webmd.com |date=February 10, 2010 |access-date=August 13, 2012 |url-status=live |archive-url=https://web.archive.org/web/20121112104541/http://children.webmd.com/news/20100210/genetic-mutations-linked-to-stuttering |archive-date=November 12, 2012 }}</ref><ref name="west">{{cite journal |last1=West |first1=Robert |last2=Nelson |first2=Severina |last3=Berry |first3=Mildred |title=The heredity of stuttering |journal=Quarterly Journal of Speech |date=February 1939 |volume=25 |issue=1 |pages=23–30 |doi=10.1080/00335633909380434 }}</ref><ref>{{cite journal |last1=Frigerio-Domingues |first1=Carlos |last2=Drayna |first2=Dennis |title=Genetic contributions to stuttering: the current evidence |journal=Molecular Genetics & Genomic Medicine |date=March 2017 |volume=5 |issue=2 |pages=95–102 |doi=10.1002/mgg3.276 |pmid=28361094 |pmc=5370225 }}</ref>

There is evidence that stuttering is more common in children who also have concurrent speech, language, learning or motor difficulties. For some people who stutter, congenital factors may play a role. In others, there could be added impact due to stressful situations. However there is no evidence to suggest this as a cause.<ref name="Guitar5–6"/>

Less common causes of stuttering include neurogenic stuttering (stuttering that occurs secondary to brain damage, such as after a stroke) and psychogenic stuttering (stuttering related to a psychological condition).<ref name="Sander and Osborne" />

===History of causes===

Auditory processing deficits were proposed as a cause of stuttering due to differences in stuttering for deaf or Hard of Hearing individuals, as well as the impact of auditory feedback machines on some stuttering cases.<ref>{{harvnb|Ward|2006|pp= 46–58}}</ref>

Some possibilities of linguistic processing between people who stutter and people who do not has been proposed.<ref>{{harvnb|Ward|2006|p= 43}}</ref> Brain scans of adult stutterers have found greater activation of the right hemisphere, than of the left hemisphere, which is associated with speech. In addition, reduced activation in the left auditory cortex has been observed.<ref name="gordon"/>

The 'capacities and demands model' has been proposed to account for the heterogeneity of the disorder. Speech performance varies depending on the 'capacity' that the individual has for producing fluent speech, and the 'demands' placed upon the person by the speaking situation. Demands may be increased by internal factors or inadequate language skills or external factors. In stuttering, severity often increases when demands placed on the person's speech and language system increase.<ref>{{harvnb|Ward|2006|pp= 16–21}}</ref> However, the precise nature of the capacity or incapacity has not been delineated. Stress, or demands, can impact many disorders without being a cause.

Another theory has been that adults who stutter have elevated levels of the neurotransmitter [[dopamine]].<ref name=":4"/><ref name="watkins">{{cite journal |last1=Watkins |first1=K. E. |last2=Smith |first2=S. M. |last3=Davis |first3=S. |last4=Howell |first4=P. |title=Structural and functional abnormalities of the motor system in developmental stuttering |journal=Brain |date=3 December 2007 |volume=131 |issue=1 |pages=50–59 |doi=10.1093/brain/awm241 |pmid=17928317 |pmc=2492392 }}</ref> 

It was once thought that forcing a left-handed student to write with their right-hand caused stuttering due to [[bias against left-handed people]], but this myth died out.<ref>{{cite journal |last1=Lewis |first1=Ruth |title=The psychological approach to the preschool stutterer |journal=Canadian Medical Association Journal |date=May 1949 |volume=60 |issue=5 |pages=497–500 |pmid=18125462 |pmc=1591462 }}</ref><ref>{{cite journal |last1=Bryngelson |first1=Bryng |last2=Clark |first2=Thomas B |title=Left-Handedness and Stuttering |journal=Journal of Heredity |date=October 1933 |volume=24 |issue=10 |pages=387–390 |doi=10.1093/oxfordjournals.jhered.a103681 }}</ref><ref>{{cite journal |last1=Johnson |first1=Wendell |last2=Duke |first2=Lucile |title=Changes in Handedness Associated with Onset or Disappearance of Stuttering: Sixteen Cases |journal=The Journal of Experimental Education |date=December 1935 |volume=4 |issue=2 |pages=112–132 |doi=10.1080/00220973.1935.11010003 }}</ref>