Background Skeletal muscle fibers are classified into slow-, fast- and intermediate-twitch fibers based on the expressed myosin heavy chain (MHC) gene. Muscle composition varies according to its function. Furthermore, muscle fibers undergo structural and metabolic remodeling under physiological or pathological conditions. Hence, fiber typing quantification enables deeper insight into the conditions affecting muscle function. Huntington disease (HD) is a neurodegenerative disease caused by an expanded CAG repeat resulting in peripheral pathological events such as muscle atrophy, and mitochondrial abnormalities. A simple imaging technique to correlate mitochondrial and muscle function with the manifested severity of the expressed HD gene is missing.

Aim The goal of this study was to investigate the validity of two fiber-staining methods in detecting muscle function changes between healthy and HD patients.

Methods Either histochemical mitochondria enzymatic activity or immunofluorescence MHC protein staining was used to assess fiber typing in cross-sections of quadriceps femoris muscle obtained from open biopsies from 19 healthy controls, 20 pre-symptomatic and 17 early motor manifest HD patients. Fiber population analyses are subsequently performed to quantify each fiber type by use of automated Fiji macros.

Results Immunolabeling against MHC isoforms provided a faster and more reliable method to quantify fibers. Both techniques showed a wide variety of fiber populations existed in all groups. A higher proportion of fast-twitch fibers was found in pre-manifest HD patients while slow-twitch fibers were more in early HD patients.

Conclusion This staining-automated quantification method can be applied to identify mechanisms underlying muscle pathology in other related neurodegenerative diseases.