الفهرس 
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Abstract
Stuttering is a common and sometimes severe communication disorder of unknown primary etiology that exists in populations worldwide, and its etiology has kept controversial for a long time.
There are several theories which tried to explain the etiology of stuttering. Yet, none of these theories was satisfactory to explain the exact etiology. These theories may be organic, psychoneurotic, learning or combined theories. Organic theories explained stuttering as a disturbance of physiological and neurophysiological aspects of speech production. Psychoneurotic theories viewed the stuttering as a result of anxiety, conflict and frustration. Learning theories expressed stuttering; including both classical and operant conditioning which elaborate more argument being the most accepted among the various theories. And lastly the combined theory which suggested that stuttering is a combination of the psychoneurotic theory and the learning theory.
Many types of evidence suggest a genetic contribution to stuttering; however, the complex inheritance of this disorder has hindered identification of these factors.
Familial clustering is extensively documented and twin studies carried out in different countries and cultures show a high degree of heritability. Nevertheless, it is clear that genetic susceptibility to stuttering is complex, multifactorial and heterogenous.
Many studies have been performed which resulted in accusation of certain chromosomes and genes to cause stuttering. Those were found to be:
• APOE–4 gene, which transmits risk for Alzheimer disease.
• FOXP2 gene on chromosome 7, which transmits risk for speech dyspraxia, autism and specific language impairment.
• Polymorphisms of three different dopaminergic genes, dopamine D2 receptor (DRD2), dopamine β hydroxylase (DβH), and dopamine transporter (DAT1).
• Mutations of NAGPA, GNPTAB and GNPTG genes (one on chromosome 12 and two on chromosome 16) which have previously been associated with metabolic diseases known as muucolipidosis II and III.
• Chromosome 21 which has been linked to Down’s syndrome.
• Other chromosomes: 1, 2, 3, 5, 9, 13, 15, 18 and 20.
Yet, according to the theory of multifactorial inheritance of stuttering, there are environmental factors that affect stutterers. Typically, these are attitudes, behaviors or events that occur in their homes. These environmental pressures include parents, speech and language environment and life events.
To conclude, recent studies and investigations revealed genetic susceptibility to stuttering; so further investigations are required for specification of the gene accused in stuttering to be taken in consideration while investigating and treating a stutterer.