Patterns of muscle fiber-type disproportion in hypotonic infants
Z. Argov, D. Gardner-Medwin, M. A. Johnson and F. L. Mastaglia
We studied the histochemical characteristics of muscle in five hypotonic
infants. A number of different patterns of disproportion in the sizes and
numbers of type 1 and type 2 fibers were found. In three cases, type 1
fibers were smaller than type 2 fibers and type 2b or 2c fibers were
largest. In one case, type 2 fibers were smaller than type 1 fibers and
were reduced in number, while in a case of Prader-Willi syndrome there was
a preponderance of type 2 fibers that were smaller than type 1 fibers. Type
2c fibers were increased in number in all but one case. We postulate that
these various patterns of fiber-type disproportion are the result of
altered neural influences leading to impaired maturation of type 1 or type
2 motor units.
