Features include myopathy, (congenital fiber type
disproportion, i.e., type I muscle fibers are significantly smaller than type II fibers
(normally about the same size), and a predominance of type I fibers by numbers
(normally about equal)), nonprogressive hypotonia, facial malformations (hypertelorism, broad nasal root,
long philtrum, mouth held open, high-arched and narrow palate, microdontia),
delayed bone age with abnormal ossification, pectus excavatum, seizures, and mental
retardation.