Quantification of muscular morphological alterations in patients with infantile and early-juvenile Pompe disease

Aims: Patients with infantile and early-juvenile Pompe disease (glycogen storage disease type II) show a variable degree of a vacuolar myopathy with pathological glycogen deposits in periodic acid-Schiff (PAS) stained sections. Enzyme replacement therapy (ERT) is available, but response to therapy is highly variable. The aim of this study was to develop a technique that allows quantifying morphological alterations in muscle tissue of Pompe patients.

Methods: To accomplish this, we analyzed 10 muscle biopsies before and 8 during ERT of 10 infantile and 4 early-juvenile patients. PAS stained semi thin sections from resin embedded material were analyzed by a computer associated stereology tool. Each muscle fiber was classified using a score ranging from 0 (normal: no glycogen, no vacuoles) to 5 (severe alterations: empty vacuoles). From these values we calculated a total morphological score (MoS).

Results: The MoS in patients (0.15 to 4.08) was increased compared with the controls (0 to 0.05) and was insignificantly higher in infantile than in early-juvenile patients (2.54 ± 1.25 vs. 1.53 ± 1.33, p > 0.05). The MoS under ERT was significantly lower in patients with good response (normal development/able to walk) (0.37 ± 0.19) compared with children with moderate (improvement of symptoms/able to sit) (3.3 ± 0.07), or poor response (no improvement at all) (3.8 ± 0.40) (p < 0.005). The MoS in muscle biopsies before ERT was lower in patients with good response (1.20 ± 0.78) compared with those with only moderate (2.64 ± 0.86) response, p < 0.05.

Conclusion: These data show that a precise quantification of muscle pathology in small resin embedded muscle biopsies from children with Pompe disease is easily achieved by the described technique, and that this allows an evaluation of morphological changes before and during ERT.