Genetics or inheritance
Here we are talking about the characteristics that the person is born with. Sometimes we read about "nature versus nurture", the crossing point between what is inherited and the environment within which we are brought up.
For example, it can sometimes be quite easy to guess where eye colour or height came from with our own parents and grandparents. It is not so easy to explain personality traits, although you do hear people saying "stubborn, just like his grandad"! Character is probably a mixture of both "nature" and "nurture".
Stammering also seems to be a mixture of both nature and nurture. For some there is a definite genetic link, a blood relative who has had or still has a stammer. It is becoming clearer that many children do inherit a vulnerability to stammering. At the Michael Palin Centre more than half of the children we see have a blood relative who has either stammered in the past or continues to stammer. While researchers are trying to find out more about the genetic links, it will be many years before the picture is fully understood - or whether this will help us to decide which therapy is best for a particular child.
The nervous system and speech fluency
However the research is also beginning to suggest (and we don't know whether this is linked to genetics) that stammering may be a sign that the child's developing nervous system for speaking fluently may be less efficient. The implication is that therapy will be more successful in childhood before the problem becomes "hard wired" into a more adult speech system. Children's nervous systems for speaking continue to change and develop until early adulthood.
To quote Professor Anne Smith from Purdue University at the Oxford Dysfluency Conference in 2008:
"Stuttering is a neurodevelopmental disorder involving many different brain systems active for speech - including language, motor, and emotional networks. Each infant is born with a genetic makeup that contributes to his or her probability of stuttering, however whether stuttering will develop depends upon experience. To learn to speak fluently, a child's brain must develop many different neural circuits, and these circuits must interact in very precise and rapid ways. Stuttering emerges in childhood as a symptom that the brain's neural circuits for speech are not being wired normally. For this reason, early intervention is critical, because by shaping the child's experience, we can affect the ongoing wiring process in the child's rapidly developing brain. The longer the stuttering symptoms persist in early childhood, the more difficult it is for us to change the brain's wiring, and stuttering becomes a chronic, usually lifelong problem."
Boys are more vulnerable - we don't know why, but boys are more at risk of other speech, language and literacy problems too.
Oral motor skills
This is related to the planning and co-ordination of the movements of articulation - tongue, jaw, voice box, etc. Some research studies have shown differences in the oral skills of some people who stammer - these may be slower or less well co-ordinated, but are so slight that they are imperceptible without scientific measuring equipment.
Brain functioning research
Brain imaging is a new and highly complicated area of research in adults who stammer. Early findings suggest that certain aspects of speech and language may be processed in different areas of the brain in some adults who stammer. What is not yet clear is whether this is at the root of the stammering problem or a result of difficulty in talking. Since it is not ethically possible to carry out these experiments with children, the results cannot be generalised to the younger population. This type of research will be continuing and we will keep you up to date with the latest studies.