Table 1.

Twin studies of stuttering

Study (year)	Language	Number of individuals	Estimated heritability
Godai et al. (1976)	Italian	126	na
Howie (1981)	English	60	na
Andrews et al. (1991)		7620	.71
Felsenfeld et al. (2000)		37	.70
Ooki (2005)	Japanese	3792	.80–.85
Dworzynski et al. (2007)	English	12,892	.60
van Beijsterveldt et al. (2010)	Dutch	21,366	.42
Fagnani et al. (2011)	Danish	22,216	.81–.84
Rautakoski et al. (2012)	Finnish	2289	.82