Genetics of Dyslexia and Left Handedness
is strongly hereditary, and so is whether you are right or left handed.
Furthermore dyslexia is said to be commoner in people who have weakly
established lateralisation and are neither strongly right or left handed.
So we have been using genetic linkage techniques in our dyslexic families
to look for chromosomal sites that may be linked to left versus right
hand skill as well as to reading. Ours was the first genetic screen covering
all the human chromosomes that has been carried out for handedness.
But we did not find any special relationship between reading problems
and handedness; relative hand skill was the same in our dyslexic families
as in the population at large. There wasn’t a strong tendency to
mixed handedness or non-right handedness. Nevertheless we did find a very
strong genetic linkage of relative hand skill to a site on chromosome
2, although this was not strongly linked to reading ability.
Even though non right handedness did not seem to be strongly associated
with reading problems, overall motor dexterity did correlate with reading
ability. The faster they were at moving pegs from one set of holes to
another with either hand, the better they were at reading. Thus accurate
motor timing and coordination seem to be conducive to good reading.
Another condition which is thought to be associated with non-right handedness
is schizophrenia, and both traits are often accompanied by lack of the
normal brain asymmetry favouring the left side. A similar site on chromosome
2 to that which we found was linked to handedness, seems also to be linked
to schizophrenia/schizoaffective disorder.
Just recently we’ve found that this shared linkage is only seen
in chromosomal regions inherited from the father. Thus this site on Chromosome
2 inherited from the father may contain genes that affect the lateralisation
of brain development. This may contribute to non- right handedness, weak
language development and to schizophrenic traits, but only indirectly