The possible causes of the sex ratio in stuttering and its implications

The incidence of stuttering has always been reported to be higher in males than in females. Possible causes of the unequal sex ratio include various ascertainment biases, incomplete reporting, social role differences, X-linked inheritance, or a combination of environmental and genetic elements. Each of these factors has been examined against data collected in the large family study of stuttering, and all but one have been eliminated. Only the gene-environment interaction hypothesis can be supported by the data. Statistical analysis confirms that the sex effect in stuttering is real and supports a threshold model for the sex difference. We conclude that the possibility of differences between males and females must be considered in any etiological research in stuttering.