Onengut et al. (2004) reported 2 brothers with hyaline body myopathy; 1 of the brothers recalled weakness from childhood, but did not become severely symptomatic until age 28, whereas the other brother was asymptomatic until age 33 years. ... Onengut et al. (2004) reported 2 brothers with hyaline body myopathy; 1 of the brothers recalled weakness from childhood, but did not become severely symptomatic until age 28, whereas the other brother was asymptomatic until age 33 years. Both patients showed scapuloperoneal weakness and atrophy with an elevated creatine kinase (2- to 3-fold increase). The brother with earlier onset also had a long face, high-arched palate, and decreased cardiac systolic function. Muscle biopsies of both patients showed variation in fiber size with marked type I fiber predominance. Approximately 15 to 20% of the fibers had central nuclei. The most striking finding was the presence of subsarcolemmal hyalinized structures which were present in 25 to 30% of type I fibers. The hyalinized structures lacked reactivity for periodic acid Schiff (PAS) and oxidative enzymes, and stained positive for ATPase at pH 4.3.